Transport Layer: UDP and TCP CS491G: Computer Networking Lab V. Arun Transport Layer 3-1 Slides...

Transport Layer UDP and TCP

CS491G Computer Networking Lab

V Arun

Transport Layer 3-1Slides adapted from Kurose and Ross

Transport Layer 3-2

Transport Layer Outline

1 transport-layer services

2 multiplexing and demultiplexing

3 connectionless transport UDP

4 connection-oriented transport TCP segment structure reliable data

transfer flow control connection

management5 principles of

congestion control6 TCP congestion

control

Transport Layer 3-3

Transport services and protocols

provide logical communication between app processes running on different hosts

transport protocols run in end systems send side breaks app

messages into segments passes to network layer

recv side reassembles segments into messages passes to app layer

more than one transport protocol available to apps Internet TCP and UDP

application

transportnetworkdata linkphysical

logical end-end transport

application


Transport Layer 3-4

Transport vs network layer network layer

logical communication between hosts

transport layer logical communication between processes relies on and

enhances network layer services

12 kids in Annrsquos house sending letters to 12 kids in Billrsquos house

hosts = houses processes = kids app messages =

letters in envelopes transport protocol =

Ann and Bill who demux to in-house siblings

network-layer protocol = postal service

household analogy

Transport Layer 3-5

Internet transport-layer protocols

reliable in-order delivery (TCP) congestion control flow control connection setup

unreliable unordered delivery UDP no-frills extension of

ldquobest-effortrdquo IP services not

available delay guarantees bandwidth

guarantees

application


application


networkdata linkphysical








Transport Layer 3-6









control

Transport Layer 3-7

Multiplexingdemultiplexing

process

socket

use header info to deliverreceived segments to correct socket

demultiplexing at receiverhandle data from multiplesockets add transport header (later used for demultiplexing)

multiplexing at sender

transport

application

physical

link

network

P2P1

transport

application

physical

link

network

P4

transport

application

physical

link

network

P3

Transport Layer 3-8

How demultiplexing works

host receives IP datagrams each datagram has source and

destination IP address each datagram carries one

transport-layer segment each segment has source and

destination port number host uses IP addresses amp port

numbers to direct segment to right socket

source port dest port

32 bits

applicationdata

(payload)

other header fields

TCPUDP segment format

Transport Layer 3-9

Connectionless demultiplexing

recall created socket has host-local port

DatagramSocket mySocket1 = new DatagramSocket(12534)

when host receives UDP segment checks destination IP

and port in segment directs UDP segment

to socket bound to that (IPport)

recall when creating datagram to send into UDP socket must specify

destination IP address destination port IP datagrams with same dest (IP port) but different source IP addresses andor source port numbers will be directed to same socket

Transport Layer 3-10

Connectionless demux example

DatagramSocket serverSocket = new DatagramSocket

(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

DatagramSocket mySocket1 = new DatagramSocket (5775)


source port 9157dest port 6428





Connection-oriented demux

TCP socket identified by 4-tuple source IP address source port number dest IP address dest port number

demux receiver uses all four values to direct segment to right socket

server host has many simultaneous TCP sockets each socket identified

by its own 4-tuple web servers have

different socket each client non-persistent HTTP

will have different socket for each request


Connection-oriented demux example

transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2

source IPport A9157dest IP port B80

source IPport B80dest IPport A9157

host IP address

A

host IP address

C

network

P6P5P3

source IPport C5775dest IPport B80


three segments all destined to IP address B dest port 80 are demultiplexed to different sockets

server IP

address B

server socket also port 80



transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

server socket also port 80threaded server










control


UDP User Datagram Protocol [RFC 768] no frills bare bones

transport protocol for ldquobest effortrdquo service UDP segments may be lost delivered out-of-

order connectionless

no sender-receiver handshaking

each UDP segment handled independently

UDP uses streaming

multimedia apps (loss tolerant rate sensitive)

DNS SNMP

reliable transfer over UDP add reliability at

application layer application-specific

error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum

length in bytes of UDP segment

including header

no connection establishment (which can add delay)

simple no connection state at sender receiver

small header size no congestion control

UDP can blast away as fast as desired

why is there a UDP


UDP checksum

sender treat segment contents

including header fields as sequence of 16-bit integers

checksum addition (onersquos complement sum) of segment contents

sender puts checksum value into UDP checksum field

receiver compute checksum of

received segment check if computed

checksum equals checksum field value NO - error detected YES - no error detected

But maybe errors nonetheless More later hellip

Goal detect ldquoerrorsrdquo (flipped bits) in segments


Internet checksum exampleexample add two 16-bit integers

1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

Note when adding numbers a carryout from the most significant bit needs to be added to the

result

Q1 Sockets and multiplexing TCP uses more information in packet

headers in order to demultiplex packets compared to UDPA TrueB False


Q2 Sockets UDP Suppose we use UDP instead of TCP under

HTTP for designing a web server where all requests and responses fit in a single packet Suppose a 100 clients are simultaneously communicating with this web server How many sockets are respectively at the server and at each clientA 11B 21C 2002D 1001E 101 1


Q3 Sockets TCP

Suppose a 100 clients are simultaneously communicating with (a traditional HTTPTCP) web server How many sockets are respectively at the server and at each clientA 11B 21C 2002D 1001E 101 1


Q4 Sockets TCP

Suppose a 100 clients are simultaneously communicating with (a traditional HTTPTCP) web server Do all of the sockets at the server have the same server-side port numberA YesB No


Q5 UDP checksums Letrsquos denote a UDP packet as (checksum

data) ignoring other fields for this question Suppose a sender sends (0010 1110) and the receiver receives (00111110) Which of the following is true of the receiverA Thinks the packet is corrupted and

discards the packetB Thinks only the checksum is corrupted

and delivers the correct data to the application

C Can possibly conclude that nothing is wrong with the packet

D A and CTransport Layer 3-23










control


TCP Overview RFCs 79311221323 2018 2581

full duplex data bi-directional data flow

in same connection MSS maximum

segment size connection-oriented

handshaking (exchange of control msgs) inits sender receiver state before data exchange

flow controlled sender will not

overwhelm receiver

point-to-point one sender one

receiver reliable in-order

byte steam no ldquomessage

boundariesrdquo pipelined

TCP congestion and flow control set window size


TCP segment structure


32 bits

applicationdata

(variable length)

sequence number

acknowledgement number

receive window

Urg data pointerchecksum

FSRPAUheadlen

notused

options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)


TCP seq numbers ACKssequence numbers

byte stream ldquonumberrdquo of first byte in segmentrsquos data

acknowledgementsseq of next byte expected from other side

cumulative ACKQ how receiver handles out-of-order segmentsA TCP spec doesnrsquot say - up to implementor


sequence number


checksum

rwnd

urg pointer

incoming segment to sender

A

sent ACKed

sent not-yet ACKed(ldquoin-flightrdquo)

usablebut not yet sent

not usable

window size N

sender sequence number space


sequence number


checksum

rwnd

urg pointer

outgoing segment from sender


TCP seq numbers ACKs

Usertypes

lsquoCrsquo

host ACKsreceipt

of echoedlsquoCrsquo

host ACKsreceipt oflsquoCrsquo echoesback lsquoCrsquo

simple telnet scenario

Host BHost A

Seq=42 ACK=79 data = lsquoCrsquo


Seq=43 ACK=80


TCP round trip time timeoutQ how to set TCP

timeout value longer than RTT

but RTT varies too short

premature timeout unnecessary retransmissions

too long slow reaction to segment loss

Q how to estimate RTT

SampleRTT measured time from segment transmission until ACK receipt ignore retransmissions

SampleRTT will vary want estimated RTT ldquosmootherrdquo average several

recent measurements not just current SampleRTT


RTT gaiacsumassedu to fantasiaeurecomfr

100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)

SampleRTT Estimated RTT

EstimatedRTT = (1- )EstimatedRTT + SampleRTT exponential weighted moving average influence of past sample decreases

exponentially fast typical value = 0125

TCP round trip time timeout

RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)


timeout interval EstimatedRTT plus ldquosafety marginrdquo large variation in EstimatedRTT -gt larger safety margin

estimate SampleRTT deviation from EstimatedRTT

DevRTT = (1-)DevRTT + |SampleRTT-EstimatedRTT|


(typically = 025)

TimeoutInterval = EstimatedRTT + 4DevRTT

estimated RTT ldquosafety marginrdquo










control


TCP reliable data transfer TCP creates rdt

service on top of IPrsquos unreliable service pipelined segments cumulative acks

bull selective acks often supported as an option

single retransmission timer

retransmissions triggered by timeout events duplicate acks

letrsquos initially consider simplified TCP sender ignore duplicate acks ignore flow control

congestion control


TCP sender eventsdata rcvd from app create segment

with seq (= byte-stream number of first data byte in segment)

start timer if not already running (for oldest unacked segment) TimeOutInterval =

smoothed_RTT + 4deviation_RTT

timeout retransmit segment

that caused timeout restart timer ack rcvd if ack acknowledges

previously unacked segments update what is

known to be ACKed (re-)start timer if still

unacked segments


TCP sender (simplified)

waitfor

event

NextSeqNum = InitialSeqNumSendBase = InitialSeqNum

create segment seq NextSeqNumpass segment to IP (ie ldquosendrdquo)NextSeqNum = NextSeqNum + length(data) if (timer currently not running) start timer

data received from application above

retransmit not-yet-acked segment with smallest seq start timer

timeout

if (y gt SendBase) SendBase = y SendBasendash1 last cumulatively ACKed byte if (there are currently not-yet-acked segments) (re-)start timer else stop timer

ACK received with ACK field value y


TCP retransmission scenarios

lost ACK scenario

Host BHost A

Seq=92 8 bytes of data

ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100

Seq=92 8bytes of data

tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120


TCP ACK generation [RFC 1122 RFC

2581]

event at receiver

arrival of in-order segment withexpected seq All data up toexpected seq already ACKed

arrival of in-order segment withexpected seq One other segment has ACK pending

arrival of out-of-order segmenthigher-than-expect seq Gap detected

arrival of segment that partially or completely fills gap

TCP receiver action

delayed ACK Wait up to 500msfor next segment If no next segmentsend ACK

immediately send single cumulative ACK ACKing both in-order segments

immediately send duplicate ACK indicating seq of next expected byte

immediate send ACK provided thatsegment starts at lower end of gap


TCP fast retransmit time-out period

often relatively long long delay before

resending lost packet detect lost

segments via duplicate ACKs sender often sends

many segments back-to-back

if segment is lost there will likely be many duplicate ACKs

if sender receives 3 ACKs for same data(ldquotriple duplicate ACKsrdquo) resend unacked segment with smallest seq

likely that unacked segment lost so donrsquot wait for timeout

TCP fast retransmit

(ldquotriple duplicate ACKsrdquo)


X

fast retransmit after sender receipt of triple duplicate ACK

Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control


TCP flow controlapplication

process

TCP socketreceiver buffers

TCPcode

IPcode

application

OS

receiver protocol stack

application may remove data from

TCP socket buffers hellip

hellip slower than TCP

receiver is delivering(sender is sending)

from sender

receiver controls sender so sender wonrsquot overflow receiverrsquos buffer by transmitting too much too fast

flow control


TCP flow control

buffered data

free buffer spacerwnd

RcvBuffer

TCP segment payloads

to application process

receiver ldquoadvertisesrdquo free buffer space by including rwnd value in TCP header of receiver-to-sender segments RcvBuffer size can be

set via socket options most operating systems

auto-adjust RcvBuffer sender limits amount

of unacked (ldquoin-flightrdquo) data to receiverrsquos rwnd value to ensure receive buffer will not overflow

receiver-side buffering










control


Connection Managementbefore exchanging data senderreceiver

ldquohandshakerdquo agree to establish connection (each knowing the

other willing to establish connection) agree on connection parameters

connection state ESTABconnection variables

seq client-to-server server-to-clientrcvBuffer size at serverclient

application

network

connection state ESTABconnection Variables


application

network

Socket clientSocket = newSocket(hostnameport

number)

Socket connectionSocket = welcomeSocketaccept()


Q will 2-way handshake always work in network

variable delays retransmitted messages

(eg req_conn(x)) due to message loss

message reordering canrsquot ldquoseerdquo other side

2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)

Agreeing to establish a connection



2-way handshake failure scenarios

retransmitreq_conn(

x)

ESTAB

req_conn(x)

half open connection(no client)

client terminat

es

serverforgets x

connection x completes

retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)

data(x+1) acceptdata(x+1)

connection x completes server

forgets x


TCP 3-way handshake

SYNbit=1 Seq=x

choose init seq num xsend TCP SYN msg

ESTAB

SYNbit=1 Seq=yACKbit=1 ACKnum=x+1

choose init seq num ysend TCP SYNACKmsg acking SYN

ACKbit=1 ACKnum=y+1

received SYNACK(x) indicates server is livesend ACK for SYNACK

this segment may contain client-to-server data

received ACK(y) indicates client is live

SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN


TCP 3-way handshake FSM

closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)

SYNACK(seq=yACKnum=x+1)create new socket for

communication back to client

SYNACK(seq=yACKnum=x+1)

ACK(ACKnum=y+1)ACK(ACKnum=y+1)


TCP closing a connection client server each close their side of

connection send TCP segment with FIN bit = 1

respond to received FIN with ACK on receiving FIN ACK can be combined with

own FIN simultaneous FIN exchanges can be

handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1

ACKbit=1 ACKnum=x+1 wait for server

close

can stillsend data

can no longersend data

LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED

TCP closing a connection

FIN_WAIT_1 FINbit=1 seq=xcan no longersend but can receive data

clientSocketclose()

client state server state

ESTABESTAB

TCP Overall state machine











control


congestion informally ldquotoo many sources sending

too much data too fast for network to handlerdquo

different from flow control manifestations

lost packets (buffer overflow at routers)

long delays (queueing in router buffers)

a top-10 problem

Principles of congestion control


Causescosts of congestion scenario 1

two senders two receivers

one router infinite buffers

output link capacity R

no retransmission

maximum per-connection throughput R2

unlimited shared output link buffers

Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin

large delays as arrival rate in approaches capacity


one router finite buffers sender retransmission of timed-out packet

app-layer input = app-layer outputin = out

transport-layer input includes retransmissions rsquoin

ge in

finite shared output link buffers

Host A

in original data

Host B

outin original data plus

retransmitted data



idealization perfect knowledge

sender sends only when router buffers available


in original dataoutin original data plus

retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space

Idealization known loss packets can be lost dropped at router due to full buffers

sender only resends if packet known to be lost


A

Host B



retransmitted data

free buffer space




R2

R2in

out

when sending at R2 some packets are retransmissions but asymptotic goodput is still R2 (why)

A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out

when sending at R2 some packets are retransmissions including duplicated that are delivered

Host B

Realistic duplicates packets can be lost

dropped at router due to full buffers

sender times out prematurely sending two copies both of which are delivered



R2

out


ldquocostsrdquo of congestion more work (retrans) for given ldquogoodputrdquo unneeded retransmissions link carries multiple

copies of pkt decreasing goodput

R2in

Causescosts of congestion scenario 2 Realistic duplicates packets can be lost




four senders multihop paths timeoutretransmit

Q what happens as in and rsquo

in increase


Host A out


Host B

Host CHost D

in original data

in original data plus

retransmitted data

A as red rsquoin increases all

arriving blue pkts at upper queue are dropped blue throughput 0


another ldquocostrdquo of congestion when packet dropped any ldquoupstream

bandwidth used for that packet wasted


C2

C2

ou

t

inrsquo


Approaches towards congestion controltwo broad approaches towards congestion

controlend-end

congestion control

no explicit feedback from network

congestion inferred from end-system observed loss delay

approach taken by TCP

network-assisted congestion control

routers provide feedback to end systemssingle bit indicating congestion (SNA DECbit TCPIP ECN ATM)

explicit rate for sender to send at


Case study ATM ABR congestion control

ABR available bit rate

ldquoelastic servicerdquo if senderrsquos path

ldquounderloadedrdquo sender should

use available bandwidth

if senderrsquos path congested sender throttled

to minimum guaranteed rate

RM (resource management) cells

sent by sender interspersed with data cells

bits in RM cell set by switches (ldquonetwork-assistedrdquo) NI bit no increase in rate

(mild congestion) CI bit congestion

indication RM cells returned to sender

by receiver with bits intact



two-byte ER (explicit rate) field in RM cell congested switch may lower ER value in cell sendersrsquo send rate thus max supportable rate on path

EFCI bit in data cells set to 1 in congested switch if data cell preceding RM cell has EFCI set receiver

sets CI bit in returned RM cell

RM cell data cell










control


TCP congestion control additive increase multiplicative decrease

approach sender increases transmission rate (window size) probing for usable bandwidth until loss occurs additive increase increase cwnd by 1

MSS every RTT until loss detected multiplicative decrease cut cwnd in half

after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e

AIMD saw toothbehavior probing

for bandwidth

additively increase window size helliphellip until loss occurs (then cut window in half)

time


TCP congestion control window

sender limits transmission

cwnd is dynamic function of perceived congestion

TCP sending rate roughly send

cwnd bytes wait RTT for ACKS then send more bytes

last byteACKed sent not-

yet ACKed(ldquoin-flightrdquo)

last byte sent

cwnd

LastByteSent -LastByteAcked

lt cwnd


rate ~~cwnd

RTTbytessec


TCP Slow Start when connection

begins increase rate exponentially until first loss event initially cwnd = 1 MSS double cwnd every

RTT done by incrementing cwnd upon every ACK

summary initial rate is slow but ramps up exponentially fast

Host A

one segment

RT

T

Host B

time

two segments

four segments


TCP detecting reacting to loss

loss indicated by timeout cwnd set to 1 MSS window then grows exponentially (as in slow start) to threshold

then grows linearly loss indicated by 3 duplicate ACKs TCP RENO

dup ACKs indicate network capable of delivering some segments cwnd is cut in half window then grows linearly

TCP Tahoe always sets cwnd to 1 (timeout or 3 duplicate acks)


Q when should the exponential increase switch to linear

A when cwnd gets to 12 of its value before timeout

Implementation variable ssthresh on loss event ssthresh is set to 12 of cwnd just before loss event

TCP slow start cong avoidance


Summary TCP Congestion Control

timeoutssthresh = cwnd2

cwnd = 1 MSSdupACKcount = 0

retransmit missing segment

cwnd gt ssthresh

congestionavoidance

cwnd = cwnd + MSS (MSScwnd)dupACKcount = 0

transmit new segment(s) as allowed

new ACK

dupACKcount++

duplicate ACK

fastrecovery

cwnd = cwnd + MSStransmit new segment(s) as allowed

duplicate ACK

ssthresh= cwnd2cwnd = ssthresh + 3


dupACKcount == 3

timeoutssthresh = cwnd2cwnd = 1 dupACKcount = 0retransmit missing segment

ssthresh= cwnd2cwnd = ssthresh + 3retransmit missing segment

dupACKcount == 3cwnd = ssthreshdupACKcount = 0

New ACK

slow start




cwnd = cwnd+MSSdupACKcount = 0transmit new segment(s) as allowed

new ACKdupACKcount++

duplicate ACK

cwnd = 1 MSS

ssthresh = 64 KBdupACKcount = 0

NewACK

NewACK

NewACK


TCP throughput Simplistic model avg TCP thruput as function of window

size RTT ignore slow start assume always data to send

W window size (measured in bytes) where loss occurs avg window size ( in-flight bytes) is frac34 W avg throughput is 34W per RTT

W

W2

avg TCP thruput = 34W

RTTbytessec

In practice W not known or fixed so this model is too simplistic to be useful


TCP throughput More practical model Throughput in terms of segment loss

probability L round-trip time T and maximum segment size M [Mathis et al 1997]

TCP throughput = 122 MT L


TCP futures TCP over ldquolong fat pipesrdquo example 1500 byte segments 100ms

RTT want 10 Gbps throughput requires W = 83333 in-flight segments

as per the throughput formula

to achieve 10 Gbps throughput need a loss rate of L = 210-10 ndash an unrealistically small loss rate

new versions of TCP for high-speed

TCP throughput = 122 MSSRTT L

TCP throughput wrap-up

Assume sender window cwnd receiver window rwnd bottleneck capacity C round-trip time T path loss rate L maximum segment size MSS Then Instantaneous TCP throughput =

bull min(C cwndTrwndT) Steady-state TCP throughput =

bull min(C 122M(TradicL))



fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK

TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2


Why is TCP fairtwo competing sessions additive increase gives slope of 1 as throughout

increases multiplicative decrease decreases throughput

proportionally R

R

equal bandwidth share

Connection 1 throughput

Con

nect

ion

2 th

roug

h pu t

congestion avoidance additive increaseloss decrease window by factor of 2



Fairness (more)Fairness and UDP multimedia apps

often do not use TCP rate throttling by

congestion control can hurt streaming quality

instead use UDP send audiovideo

at constant rate tolerate packet loss

Fairness parallel TCP connections

application can open many parallel connections between two hosts

web browsers do this eg link of rate R with 9

existing connections new app asks for 1 TCP gets

R10 new app asks for 11 TCPs gets

R2




Transport vs network layer


Slide 6







Slide 13

Slide 14

UDP User Datagram Protocol [RFC 768]

UDP segment header

UDP checksum

Internet checksum example

Q1 Sockets and multiplexing

Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32

TCP reliable data transfer

TCP sender events



Slide 37

TCP ACK generation [RFC 1122 RFC 2581]

TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44

Connection Management


Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63

Approaches towards congestion control


Slide 66

Slide 67



TCP Slow Start




TCP throughput Simplistic model

TCP throughput More practical model

TCP futures TCP over ldquolong fat pipesrdquo


TCP Fairness

Why is TCP fair

Fairness (more)

Transport Layer 3-2









control

Transport Layer 3-3







application



application


Transport Layer 3-4










household analogy

Transport Layer 3-5






guarantees

application


application










Transport Layer 3-6









control

Transport Layer 3-7


process

socket




transport

application

physical

link

network

P2P1

transport

application

physical

link

network

P4

transport

application

physical

link

network

P3

Transport Layer 3-8








32 bits

applicationdata

(payload)

other header fields


Transport Layer 3-9












(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

















transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

Transport Layer 3-3







application



application


Transport Layer 3-4










household analogy

Transport Layer 3-5






guarantees

application


application










Transport Layer 3-6









control

Transport Layer 3-7


process

socket




transport

application

physical

link

network

P2P1

transport

application

physical

link

network

P4

transport

application

physical

link

network

P3

Transport Layer 3-8








32 bits

applicationdata

(payload)

other header fields


Transport Layer 3-9












(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

















transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

Transport Layer 3-4










household analogy

Transport Layer 3-5






guarantees

application


application










Transport Layer 3-6









control

Transport Layer 3-7


process

socket




transport

application

physical

link

network

P2P1

transport

application

physical

link

network

P4

transport

application

physical

link

network

P3

Transport Layer 3-8








32 bits

applicationdata

(payload)

other header fields


Transport Layer 3-9












(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

















transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

Transport Layer 3-5






guarantees

application


application










Transport Layer 3-6









control

Transport Layer 3-7


process

socket




transport

application

physical

link

network

P2P1

transport

application

physical

link

network

P4

transport

application

physical

link

network

P3

Transport Layer 3-8








32 bits

applicationdata

(payload)

other header fields


Transport Layer 3-9












(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

















transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

Transport Layer 3-6









control

Transport Layer 3-7


process

socket




transport

application

physical

link

network

P2P1

transport

application

physical

link

network

P4

transport

application

physical

link

network

P3

Transport Layer 3-8








32 bits

applicationdata

(payload)

other header fields


Transport Layer 3-9












(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

















transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

Transport Layer 3-7


process

socket




transport

application

physical

link

network

P2P1

transport

application

physical

link

network

P4

transport

application

physical

link

network

P3

Transport Layer 3-8








32 bits

applicationdata

(payload)

other header fields


Transport Layer 3-9












(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

















transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

Transport Layer 3-8








32 bits

applicationdata

(payload)

other header fields


Transport Layer 3-9












(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

















transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

Transport Layer 3-9












(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

















transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)




(6428)

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

















transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)











transport

application

physical

link

network

P3transport

app

physical

link

P4

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B




transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



transport

application

physical

link

network

P3transport

app

physical

link

transport

application

physical

link

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4











control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)










control







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)







UDP uses streaming


DNS SNMP



error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)


UDP checksum












1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


result







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)







Q3 Sockets TCP



Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

Q4 Sockets TCP


















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)
















control








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)








overwhelm receiver









32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)




32 bits

applicationdata

(variable length)

sequence number


receive window


FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)







sequence number


checksum

rwnd

urg pointer


A

sent ACKed



not usable

window size N



sequence number


checksum

rwnd

urg pointer




Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



Usertypes

lsquoCrsquo

host ACKsreceipt




Host BHost A



Seq=43 ACK=80













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)













100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)





RTT

(mill

iseco

nds)


sampleRTT

EstimatedRTT

time (seconds)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)






(typically = 025)












control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)










control








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)








congestion control










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)










unacked segments



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



waitfor

event





timeout





lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



lost ACK scenario

Host BHost A


ACK=100


Xtim

eo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


tim

eo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



X

cumulative ACK

Host BHost A


ACK=100


tim

eo

ut


ACK=120



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



2581]

event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)










TCP fast retransmit



X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)


X


Host BHost A


ACK=100

tim

eo

ut ACK=100

ACK=100

ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)










control



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



process


TCPcode

IPcode

application

OS






from sender


flow control


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)


TCP flow control

buffered data


RcvBuffer

















control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)










control







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)







application

network



application

network


number)







2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)






2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose xreq_conn(x)

ESTAB

ESTABacc_conn(x)





retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)




retransmitreq_conn(

x)

ESTAB

req_conn(x)


client terminat

es

serverforgets x


retransmitreq_conn(

x)

ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminat

es

ESTAB

choose xreq_conn(x)

ESTAB

acc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



closed

listen

SYNrcvd

SYNsent

ESTAB


number)

SYN(seq=x)


SYN(x)










handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)






handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()


ESTABESTAB












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)












control







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)







a top-10 problem







no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)






no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin






ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)





ge in


Host A

in original data

Host B


retransmitted data







retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)






retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



retransmitted data

copy

no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)


R2

out




R2in







in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)




in increase


Host A out


Host B

Host CHost D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)





C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



controlend-end

congestion control


























RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)




















RM cell data cell










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)










control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)









last byte sent

cwnd


lt cwnd


rate ~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)






Host A

one segment

RT

T

Host B

time

two segments

four segments

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

















cwnd gt ssthresh

congestionavoidance



new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






duplicate ACK

cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)





W

W2


RTTbytessec




















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)



















TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)












R2






Slide 6







Slide 13

Slide 14


UDP segment header

UDP checksum



Q2 Sockets UDP

Q3 Sockets TCP

Q4 Sockets TCP

Q5 UDP checksums

Slide 24




Slide 28


Slide 30

Slide 31

Slide 32


TCP sender events



Slide 37


TCP fast retransmit

Slide 40

Slide 41

TCP flow control

Slide 43

Slide 44



Slide 47

TCP 3-way handshake



Slide 51


Slide 53




Slide 57

Slide 58

Slide 59

Slide 60

Slide 61


Slide 63



Slide 66

Slide 67



TCP Slow Start








TCP Fairness

Why is TCP fair

Fairness (more)

Transport Layer: UDP and TCP CS491G: Computer Networking Lab V. Arun Transport Layer 3-1 Slides...

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Transcript of Transport Layer: UDP and TCP CS491G: Computer Networking Lab V. Arun Transport Layer 3-1 Slides...