CSIT 561: CSIT 561: Computer Networks“Computer Networks”

CSIT 561: “Computer Networks”CSIT 561: Computer Networks

Fall 2009HKUST

Introduction 1-1

Course InfoCourse Info

Instructors:InstructorsDr. Jogesh K. Muppala: http://www.cs.ust.hk/~muppala/ Dr. Qian Zhang: http://www.cs.ust.hk/~qianzh

Course web sitehttp://www.cse.ust.hk/~muppala/csit561/contains all notes, announcements, etc. Check it regularly!L t h d lLecture schedule

Track 15: (Wed 7:30 pm - 10:20 pm) Track 14: (Thurs 3:30 pm 6:20 pm)

Introduction 1-2

Track 14: (Thurs 3:30 pm - 6:20 pm)


Textbook: James Kurose and Keith Ross Textbook James Kurose and Keith Ross Computer Networking: A Top Down Approach, 5th ed. Addison Wesley, 2009http://www.aw-bc.com/kurose_ross/ with useful resource material

The useful links and also the lab materials onlinematerials online

Introduction 1-3


Grading schemegOption 1

• Homework (3) 45 points (15 points for each)• Mid-Term Exam 25 pointsMid-Term Exam 25 points• Final Exam 30 points

Option 2• Homework (2) 30 points• Homework (2) 30 points• Survey report (replace the last homework) 20 points• Mid-Term Exam 20 points• Final Exam 30 points• Final Exam 30 points

Examinations arrangement (to be confirmed)Mid-term (Oct. 10, 3:00-5:00 pm)

Introduction 1-4

Final exam (Dec. 10, 7:30-10:00 pm)

Course ScheduleCourse Schedule

I t d ti f t t ki (2 l t )Introduction of computer networking (2 lectures)

Application layer (4 lectures)

Transport layer (5 lectures)

Networking layer (5 lectures)g y ( )

Link Layer and Local Area Networks (3 lectures)

Mobile and wireless computing (4 lectures)Mobile and wireless computing (4 lectures)

Multimedia networking (3 lectures)

Introduction 1-5

Chapter 1Chapter 1Introduction

A note on the use of these ppt slides:The notes used in this course are substantially

Computer Networking: A Top Down Approach ,4th edition. Jim Kurose Keith Ross

The notes used in this course are substantially based on powerpoint slides developed and copyrighted by J.F. Kurose and K.W. Ross, 2007

Jim Kurose, Keith RossAddison-Wesley, July 2007.

Introduction 1-6

Chapter 1: IntroductionChapter 1 IntroductionOur goal:

G t “f l” d Overview:

Get “feel” and terminologyMore depth, detail

What’s the Internet?What’s a protocol?Network edge; hosts access

plater in courseApproach:

use Internet as

Network edge; hosts, access net, physical mediaNetwork core: packet/circuit use Internet as

examplep

switching, Internet structurePerformance: loss, delay, th h tthroughputSecurityProtocol layers service models

Introduction 1-7

Protocol layers, service modelsHistory

Chapter 1: roadmapChapter roadmap

1.1 What is the Internet?1.2 Network edge

End systems, access networks, links1.3 Network core

Circuit switching, packet switching, network structure1 4 Delay loss and throughput in packet-switched 1.4 Delay, loss and throughput in packet switched

networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History

Introduction 1-8

What’s the Internet: “nuts and bolts” view

Millions of connected computing devices:

Mobile network

Global ISP

PC

server mp ghosts = end systems

Running network H t k

Global ISPserver

wirelesslaptopcellular apps Home network

Regional ISP

cellular handheld

Communication linksFiber copper

Institutional networkwiredlinks

access points

Fiber, copper, radio, satelliteTransmission rate b d idth

router

= bandwidth

Routers: forward packets (chunks of data)

Introduction 1-9

router packets (chunks of data)

What’s the Internet: “nuts and bolts” view

Protocols control sending, receiving of msgs

Mobile network

Global ISPreceiving of msgsE.g., TCP, IP, HTTP, Skype, Ethernet

H t k

Global ISP

Internet: “network of networks”

Loosely hierarchical

Home networkRegional ISP

Loosely hierarchicalPublic Internet versus private intranet

Institutional network

Internet standardsRFC: Request for commentsIETF: Internet Engineering

Introduction 1-10

IETF: Internet Engineering Task Force

What’s the Internet: A Service ViewCommunication infrastructure enables infrastructure enables distributed applications:

Web, VoIP, email, games, f l he-commerce, file sharing

Communication services id d t provided to apps:

Reliable data delivery from source to destination“Best effort” (unreliable) data delivery

Introduction 1-11

What’s a Protocol?What s a Protocol?Human protocols:

“Wh t’ th ti ?”Network protocols:

M hi th th “What’s the time?”“I have a question”Introductions

Machines rather than humansAll communication Introductions

… specific msgs sent

All communication activity in Internet governed by protocols

… specific actions taken when msgs received, or other events

Protocols define format, order of msgs sent and

i d k or other events received among network entities, and actions

taken on msg

Introduction 1-12

transmission, receipt

What’s a Protocol?What s a Protocol?A human protocol and a computer network protocol:

Hi TCP connection

Hi

G h

TCP connectionrequest

TCP connectionGot thetime?

2:00

response

Get http://www.awl.com/kurose-ross

<file>time

Introduction 1-13

Q: Other human protocols?

Chapter 1: RoadmapChapter Roadmap





Introduction 1-14

A Closer Look at Network Structure:LNetwork edge:

li ti d h tapplications and hosts

Access networks, physical media:wired, wireless

i ti li kscommunication links

Network core:Interconnected routersNetwork of networks

Introduction 1-15

The Network Edge:The Network EdgeEnd systems (hosts):

Run application programsRun application programsE.g. Web, emailAt “edge of network” peer-peer

Client/server modelClient host requests, receives service from always on server

client/serverservice from always-on serverE.g. Web browser/server; email client/server

Peer-peer model:Minimal (or no) use of dedicated servers

Introduction 1-16

E.g. Skype, BitTorrent

Network Edge: Reliable Data Transfer ServiceService

Goal: data transfer TCP service [RFC 793]Goal: data transfer between end systemsHandshaking: setup ( f ) d

TCP service [RFC 793]Reliable, in-order byte-stream data transfer

(prepare for) data transfer ahead of time

Hello, hello back human

Loss: acknowledgements and retransmissions

Flow control:H o, h o ac human protocolSet up “state” in two communicating hosts

Flow controlSender won’t overwhelm receiver

Congestion control:mmu gTCP - Transmission Control Protocol

I ’ li bl d

Congestion control:Senders “slow down sending rate” when n t k n st d

Introduction 1-17

Internet’s reliable data transfer service

network congested

Network Edge: Best Effort (Unreliable) Data Transfer ServiceData Transfer Service

Goal: data transfer App’s using TCP:Goal: data transfer between end systems

same as before!DP D

App s using TCP:HTTP (Web), FTP (file transfer), Telnet ( l ) P UDP - User Datagram

Protocol [RFC 768]: Connectionless

(remote login), SMTP (email)

Connectionless Unreliable data transfer

App’s using UDP:streaming media

No flow controlNo congestion control

streaming media, teleconferencing, DNS, Internet telephony

Introduction 1-18

Access Networks and Physical Mediay

Q: How to connect end systems to edge router?systems to edge router?Residential access netsInstitutional access Institutional access networks (school, company)M bil t kMobile access networks

Keep in mind: B d id h (bi Bandwidth (bits per second) of access network?

Introduction 1-19

Shared or dedicated?

Residential Access: Point to Point Access

Dialup via modemD a up a mo mUp to 56Kbps direct access to router (often less)C ’t f d h t Can’t surf and phone at same time: can’t be “always on”

d l lDSL: digital subscriber linedeployment: telephone company (typically)up to 1 Mbps upstream (today typically < 256 kbps)up to 1 Mbps upstream (today typically < 256 kbps)up to 8 Mbps downstream (today typically < 1 Mbps)dedicated physical line to telephone central office

Introduction 1-20

p y p

Residential Access: Cable Modems

HFC: hybrid fiber coaxHFC: hybrid fiber coaxAsymmetric: up to 30Mbps downstream, 2 Mbps upstreamIs shared broadcast medium

Network of cable and fiber attaches homes to ISP tISP router

Homes share access to router Deployment: available via cable TV companiesDeployment: available via cable TV companies

Introduction 1-21

Company Access: Local Area Networksp y

Company/univ local area network (LAN) connects network (LAN) connects end system to edge routerEthernet:

10 Mbs, 100Mbps, 1Gbps, 10Gbps EthernetM d fi ti Modern configuration: end systems connect into Ethernet switch

LANs: chapter 5

Introduction 1-22

Wireless Access NetworksShared wireless access network connects end system network connects end system to router

Via base station aka “access p int”

router

point”Wireless LANs:

802.11b/g (WiFi): 11 or 54 Mbps

basestation

g ( ) pWider-area wireless access

Provided by telco operator1Mb ll l t ~1Mbps over cellular system

(EVDO, HSDPA)Next up (?): WiMAX (10’s Mbps)

id

mobilehosts

Introduction 1-23

over wide area

Wireless TechnologiesW g

WWAN (3G,4G?)

WMAN (Wi-Max)

BluetoothUWBRFID

coverage

WLAN (Wi-Fi)

WPAN

WMAN (Wi-Max)

WPAN

Introduction 1-24

Home NetworksTypical home network components:

ADSL or cable modemADSL or cable modemRouter/firewall/NATEthernetWireless access point

wirelesslaptops

/blto/from

wirelessaccess

router/firewall

cablemodem

to/fromcable

headend

Introduction 1-25

access pointEthernet

Physical Mediay

Bit: propagates betweenTwisted Pair (TP)

Two insulated copper p p gtransmitter/rcvr pairsPhysical link: what lies b t t s itt &

Two insulated copper wires

Category 3: traditional h i 10 Mb between transmitter &

receiverGuided media:

phone wires, 10 Mbps EthernetCategory 5: 100Mb Eth tGu ded med a

Signals propagate in solid media: copper, fiber, coax

Unguided media:

100Mbps Ethernet

Unguided media:Signals propagate freely, e.g., radio

Introduction 1-26

Physical Media: Coax, Fibery ,

Coaxial cable:T t i

Fiber optic cable:Glass fiber carrying light Two concentric copper

conductorsBidirectional

Glass fiber carrying light pulses, each pulse a bitHigh-speed operation:

Baseband:Single channel on cableLegacy Ethernet

High-speed point-to-point transmission (e.g., 10’s-100’s Gps)Legacy Ethernet

Broadband:Multiple channels on cable

Low error rate: repeaters spaced far apart ; immune to electromagnetic noisecable

HFCto electromagnetic noise

Introduction 1-27

Physical Media: Radioy

Signal carried in electromagnetic spectrumN h si l “ i ”No physical “wire”BidirectionalPropagation environment effects:Propagation environment effects:

Reflection Obstruction by objectsInterferenceInterference

Multipath propagation

Signal at Receiver

Introduction 1-28

Signal at Sender

Physical Media: Radioy

Radio link types:Radio link typesTerrestrial microwave

e.g. up to 45 Mbps channelsLAN (e.g., Wifi)

11Mbps, 54 MbpsWide area (e g cellular)Wide-area (e.g., cellular)

e.g. 3G: hundreds of kbpsSatellite

Kbps to 45Mbps channel (or multiple smaller channels)270 msec end-end delayGeosynchronous versus low altitude

Introduction 1-29

Geosynchronous versus low altitude






Introduction 1-30

The Network CoreThe Network CoreMesh of interconnected routers

The fundamental question: how is data transferred through net?

Circuit switching:Circuit-switching:dedicated circuit per call: telephone netPacket-switching: data sent thru net in discrete “chunks”

Introduction 1-31

discrete chunks”

Network Core: Circuit Switchingg

End-end resources End end resources reserved for “call”Link bandwidth, switch capacityDedicated resources: no sharingsharingCircuit-like (guaranteed) performance

ll dCall setup required

Introduction 1-32

Network Core: Circuit SwitchinggNetwork resources

( b d idth) Dividing link bandwidth

“ ”(e.g., bandwidth) divided into “pieces”Pieces allocated to calls

into “pieces”Frequency divisionTime divisionPieces allocated to calls

Resource piece idle if not used by owning call

Time division

y g(no sharing)

Introduction 1-33

Circuit Switching: FDM and TDMC rcu t Sw tch ng FDM and DM

FDM 4 usersExample:

frequency

4 users

frequency

timeTDM

frequency

Introduction 1-34time

Network Core: Packet SwitchinggEach end-end data stream

divided into packetsResource contention:

A t divided into packetsUser A, B packets sharenetwork resources

Aggregate resource demand can exceed amount available

Each packet uses full link bandwidth R d d d

Congestion: packets queue, wait for link useSt d f d Resources used as needed Store and forward: packets move one hop at a time

Node receives complete packet before forwarding

Bandwidth division into “pieces”Dedicated allocationResource reservation

Introduction 1-35

Packet Switching: Statistical Multiplexingg p g

A C100 Mb/sEthernet statistical multiplexing

B1.5 Mb/s

p g

Bqueue of packetswaiting for output

link

D E

Sequence of A & B packets does not have fixed pattern, shared on demand statistical multiplexing

Introduction 1-36

TDM: each host gets same slot in revolving TDM frame

Packet-Switching: Store-and-Forwardg

R R RL

Takes L/R seconds to transmit (push out) packet

Example:L = 7 5 Mbits

R R R

transmit (push out) packet of L bits on to link or R bpsE ti k t t i

L 7.5 MbitsR = 1.5 Mbpsdelay = 15 sec

Entire packet must arrive at router before it can be transmitted on next link:

d f dstore and forwardDelay = 3L/R (assuming zero propagation delay) more on delay shortly …

Introduction 1-37

zero propagation delay)

Packet Switching versus Circuit Switchingg g

Is packet switching a “slam dunk winner?”

Great for bursty dataResource sharinggSimpler, no call setup

Excessive congestion: packet delay and lossProtocols needed for reliable data transfer, congestion control

Q: How to provide circuit like behavior?Q: How to provide circuit-like behavior?Bandwidth guarantees needed for audio/video appsStill an unsolved problem (chapter 7)

Introduction 1-38

Still an unsolved problem (chapter 7)

Internet Structure: Network of Networks

Roughly hierarchicalAt center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage

Treat each other as equalsTreat each other as equals

Ti 1 Tier 1 ISPTier-1 providers interconnect (peer)

Tier 1 ISP Tier 1 ISP(p )privately

Introduction 1-39

Tier-1 ISP: e.g., SprintT er ISP e.g., Spr nt

POP: point-of-presence

peering

to/from backbone

…peering….

to/from customers

………

Introduction 1-40


“Tier-2” ISPs: smaller (often regional) ISPsC i 1 I P ibl h i 2 I PConnect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier-2 ISPTier-2 ISPTier-2 ISP pays tier-1 ISP for

Tier-2 ISPs also peer privately with

Tier 1 ISPtier 1 ISP for connectivity to rest of Internet

Tier-2 ISP is t f

each other.

Tier 1 ISP Tier 1 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISPcustomer oftier-1 provider

Introduction 1-41



“Tier-3” ISPs and local ISPs L h (“ ”) k ( l d )Last hop (“access”) network (closest to end systems)

local l llocalISP Tier 3

Tier-2 ISPTier-2 ISP

localISPlocal

ISPlocalISP

ISP Tier 3ISP

Local and tier-3 ISPs are

Tier 1 ISPcustomers ofhigher tier ISPsconnecting



Tier-2 ISPlocal

connecting them to rest of Internet

Introduction 1-42

Tier 2 ISP Tier 2 ISPlocalISP

localISP

localISP

ISP


A packet passes through many networks!

local l llocalISP Tier 3

Tier-2 ISPTier-2 ISP

localISPlocal

ISPlocalISP

ISP Tier 3ISP

Tier 1 ISP



Tier-2 ISPlocal

Introduction 1-43

Tier 2 ISP Tier 2 ISPlocalISP

localISP

localISP

ISP






Introduction 1-44

How do Loss and Delay Occur?How do Loss and Delay Occur?Packets queue in router buffers

Packet arrival rate to link exceeds output link capacityPackets queue, wait for turn

A

packet being transmitted (delay)

A

Bpackets queueing (delay)

free (available) buffers: arriving packets

Introduction 1-45

free (available) buffers: arriving packets dropped (loss) if no free buffers

Four Sources of Packet DelayFour Sources of Packet Delay

1. Nodal processing: 2. Queueing1. Nodal processingCheck bit errorsDetermine output link

2. QueueingTime waiting at output link for transmission Depends on congestion Depends on congestion level of router

A

Bnodal

i i

Introduction 1-46

processing queueing

Delay in Packet-Switched NetworksDelay in Packet Switched Networks3. Transmission delay:

R li k b d idth (b )4. Propagation delay:

d l th f h i l li kR=link bandwidth (bps)L=packet length (bits)Time to send bits into

d = length of physical links = propagation speed in medium (~2x108 m/sec)Time to send bits into

link = L/Rmedium ( 2x10 m/sec)propagation delay = d/s

Note: s and R are very

transmission

Note: s and R are very different quantities!

Apropagation

A

B

Introduction 1-47

Bnodal

processing queueing

Caravan Analogy

t

100 km 100 km

Cars “propagate” at Time to “push” entire

toll booth

toll booth

ten-car caravan

Cars propagate at 100 km/hrToll booth takes 12 sec to

Time to push entire caravan through toll booth onto highway = 12*10 = 120 secservice a car

(transmission time)car~bit; caravan ~ packet

12*10 = 120 secTime for last car to propagate from 1st to car~bit; caravan ~ packet

Q: How long until caravan is lined up before 2nd toll

p p g2nd toll both: 100km/(100km/hr)= 1 hrA: 62 mi t s

Introduction 1-48

pbooth? A: 62 minutes

Caravan Analogy (more)

t

100 km 100 km

Yes! After 7 min 1st car

toll booth

toll booth

ten-car caravan

Cars now “propagate” at 1000 km/hrToll booth now takes 1

Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth.1 bi f k Toll booth now takes 1

min to service a carQ: Will cars arrive to

1st bit of packet can arrive at 2nd router before packet is fully Q

2nd booth before all cars serviced at 1st booth?

p ytransmitted at 1st router!

See Ethernet applet at AWL Web site

Introduction 1-49

booth? Web site

Nodal DelayNodal Delay

proptransqueueprocnodal ddddd +++=

dproc = processing delay

proptransqueueprocnodal

proc p g yTypically a few microsecs or less

dqueue = queuing delayD d ti l l i th tDepends on congestion level in the router

dtrans = transmission delay= L/R, significant for low-speed links, g p

dprop = propagation delayA few microsecs to hundreds of msecs

Introduction 1-50

Queueing Delay (revisited)Queueing Delay (revisited)

R=link bandwidth (bps)R link bandwidth (bps)L=packet length (bits)a=average packet parrival rate

traffic intensity = La/Ry

La/R ~ 0: average queueing delay smallLa/R -> 1: delays become largeLa/R > 1: more “work” arriving than can be serviced average delay infinite!

Introduction 1-51

serviced, average delay infinite!

“Real” Internet Delays and RoutesD y

What do “real” Internet delay & loss look like? yTraceroute program: provides delay measurement from source to router along end-end I t t th t ds d sti ti F ll iInternet path towards destination. For all i:

Sends three packets that will reach router i on path towards destinationRouter i will return packets to senderSender times interval between transmission and reply

3 probes

3 probes

3 probes

Introduction 1-52

pr

Packet LossPacket Loss

Queue (aka buffer) preceding link in buffer Q ( ) p ghas finite capacityPacket arriving to full queue dropped (aka lost)g q pp ( )Lost packet may be retransmitted by previous node, by source end system, or not at all

Apacket being transmitted

buffer (waiting area)

Bpacket arriving to

Introduction 1-53

packet arriving tofull buffer is lost

ThroughputThroughputThroughput: rate (bits/time unit) at which bits transferred between sender/receiver

Instantaneous: rate at given point in timeA l ( ) i d f iAverage: rate over long(er) period of time

server, withfile of F bits

to send to client

link capacityRs bits/sec

link capacityRc bits/sec

pipe that can carryfluid at rateR bits/sec)

pipe that can carryfluid at rateR bits/sec)

server sends bits (fluid) into pipe

Introduction 1-54

to send to client Rs bits/sec) Rc bits/sec)

Throughput (more)Throughput (more)Rs < Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

Rs > Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

link on end end path that constrains end end throughputbottleneck link

Introduction 1-55

link on end-end path that constrains end-end throughput

Throughput: Internet ScenarioThroughput Internet Scenario

Rs

Rs

RsPer-connection end-end

R

end end throughput: min(Rc,Rs,R/10)

Rc

Rc

Rc

c s

In practice: Rc or Rs is often

10 connections (fairly) share

cbottleneck

Introduction 1-56

10 connections (fairly) share backbone bottleneck link R bits/sec






Introduction 1-57

Protocol “Layers”Protocol LayersNetworks are complex!

M “ i ”Many “pieces”:HostsRouters

Question:Is th h f Routers

Links of various media

Is there any hope of organizing structure of

network?ApplicationsProtocols Or at least our discussion

f t k ?Hardware and software

of networks?

Introduction 1-58

Why Layering?Why Layer ng?Dealing with complex systems:

E l ll d f Explicit structure allows identification, relationship of complex system’s pieces

Layered reference model for discussionLayered reference model for discussionModularization eases maintenance, updating of system

Change of implementation of layer’s service transparent to rest of systemE g change in gate procedure doesn’t affect E.g., change in gate procedure doesn t affect rest of system

Layering considered harmful?

Introduction 1-59

y g

Internet Protocol StackInternet Protocol StackApplication: supporting network

li ti sapplicationsFTP, SMTP, HTTP

Transport: process-process data

application

transportp p ptransfer

TCP, UDPNetwork: routing of datagrams

transport

networkNetwork: routing of datagrams from source to destination

IP, routing protocolslink

Link: data transfer between neighboring network elements

PPP Ethernet

physical

Introduction 1-60

PPP, EthernetPhysical: bits “on the wire”






Introduction 1-61

Network SecurityNetwork Secur tyAttacks on Internet infrastructure:

I f ti / tt ki h t l Infecting/attacking hosts: malware, spyware, worms, unauthorized access (data stealing, user accounts)Denial of service: deny access to resources (servers, link bandwidth)

ll d d h ( h) Internet not originally designed with (much) security in mind

Original vision: “a group of mutually trusting users Original vision: a group of mutually trusting users attached to a transparent network” ☺Internet protocol designers playing “catch-up”

Introduction 1-62

Security considerations in all layers!

What Can Bad Guys Do: Malware?W y D

Spyware: Worm:Infection by downloading web page with spywareRecords keystrokes, web

Infection by passively receiving object that gets itself executedy

sites visited, upload info to collection site

Virus

Self-replicating: propagates to other hosts, usersSapphire Worm: aggregate scans/secV rus

Infection by receiving object (e.g., e-mail attachment), actively

Sapphire Worm: aggregate scans/secin first 5 minutes of outbreak (CAIDA, UWisc data)

attachment), actively executingSelf-replicating: propagate itself to other

Introduction 1-63

propagate tself to other hosts, users

Denial of Service AttacksDen al of Serv ce AttacksAttackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming g ff y gresource with bogus traffic

1 S l t t t1. Select target2. Break into hosts

around the network around the network (see malware)

3. Send packets toward target

target from compromised hosts

Introduction 1-64

Sniff, Modify, Delete Your Packetsff, fy, DPacket sniffing:

B d d ( h d E h l )Broadcast media (shared Ethernet, wireless)Promiscuous network interface reads/records all packets (e g including passwords!) passing bypackets (e.g., including passwords!) passing by

A C

src:B dest:A payloadB

Ethereal software used for end-of-chapter labs i (f ) k t iff

Introduction 1-65

is a (free) packet-snifferMore on modification, deletion later

Masquerade as youMasquerade as youIP spoofing: send packet with false source address

A C

Bsrc:B dest:A payload

B

Introduction 1-66

Masquerade as youMasquerade as youIP spoofing: send packet with false source addressRecord-and-playback: sniff sensitive info (e.g., password), and use later

Password holder is that user from system point of Password holder is that user from system point of view

CA

C

B d t A B d f

B

src:B dest:A user: B; password: foo

Introduction 1-67

Masquerade as youMasquerade as youIP spoofing: send packet with false source addressRecord-and-playback: sniff sensitive info (e.g., password), and use later

Password holder is that user from system point of Password holder is that user from system point of view

later ….. CA

C

B d t A B d f

B

src:B dest:A user: B; password: foo

Introduction 1-68



end systems, access networks, links1.3 Network core

circuit switching, packet switching, network structure1 4 Delay loss and throughput in packet-switched 1.4 Delay, loss and throughput in packet switched


Introduction 1-69

Internet History

1961: Kleinrock

1961-1972: Early packet-switching principles

The first link in the1961: Kleinrock -queueing theory shows effectiveness of packet-switching

The first link in theInternet backbone

UCLA

SRI

crashpacket switching1964: Baran - packet-switching in military nets

UCLA

The first message: LO!nets1967: ARPAnet conceived by Advanced Research Projects

What was the first message ever sent on the Internet? (LOGIN)Research Projects

Agency1969: first ARPAnet node operational

sent on the Internet? (LOGIN)

We sent an “L” - did you get the “L”? YEP!We sent an “O” - did you get the “O”? YEP!W “G” d d h “G”

Introduction 1-70

node operational We sent a “G” - did you get the “G”?

Internet History

1972

1961-1972: Early packet-switching principles

The Internet is Born! 1972:ARPAnet public demonstration

The Internet is Born!at UCLA on October 29, 1969 demonstration

NCP (Network Control Protocol) first host-host

t l

What it looked like at the end of 1969

protocol First e-mail programARPAnet has 15 nodesARPAnet has 15 nodes

Introduction 1-71

Internet History

1970: ALOHAnet satellite Cerf and Kahn’s

1972-1980: Internetworking, new and proprietary nets97 LOH n t sat t

network in Hawaii1974: Cerf and Kahn -architecture for i t ti t k

Cerf and Kahn s internetworking principles:

minimalism, autonomy -no internal changes interconnecting networks

1976: Ethernet at Xerox PARCt 70’s: i t

no internal changes required to interconnect networksbest effort service

ate70’s: proprietary architectures: DECnet, SNA, XNAlate 70’s: switching fixed

modelstateless routersdecentralized controllate 70 s: switching fixed

length packets (ATM precursor)1979: ARPAnet has 200 nodes

define today’s Internet architecture

Introduction 1-72

Internet History

1983: d l t f N ti l

1980-1990: new protocols, a proliferation of networks

1983: deployment of TCP/IP1982: SMTP e-mail

New national networks: Csnet, BITnet, NSFnet, 98 SM ma

protocol defined 1983: DNS defined f t IP

Minitel100,000 hosts connected to for name-to-IP-

address translation1985: FTP protocol

connected to confederation of networks1985 FTP protocol

defined1988: TCP congestion

t l

Introduction 1-73

control

Internet History

Early 1990’s: ARPAnet L t 1990’ 2000’

1990, 2000’s: commercialization, the Web, new apps

Early 1990 s: ARPAnet decommissioned1991: NSF lifts restrictions on commercial use of NSFnet

Late 1990’s – 2000’s:More killer apps: instant messaging, P2P file sharing

commercial use of NSFnet (decommissioned, 1995)Early 1990s: Web

H t t [B h 1945

Network security to forefrontEst. 50 million host, 100

Hypertext [Bush 1945, Nelson 1960’s]HTML, HTTP: Berners-Lee

million+ usersBackbone links running at Gbps

1994: Mosaic, later NetscapeLate 1990’s: commercialization of the Web

p

Introduction 1-74

Internet History

2007:~500 million hostsVoice, Video over IPP2P li ti BitT t P2P applications: BitTorrent (file sharing), Skype (VoIP), PPLive (video)( )More applications: YouTube, gamingWi l bilitWireless, mobility

Introduction 1-75

Introduction: SummaryIntroduct on SummaryCovered a “ton” of material!

Internet overviewYou now have:

Internet overviewWhat’s a protocol?Network edge, core,

Context, overview, “feel” of networkingMore depth detail to g , ,

access networkPacket-switching versus circuit-switching

More depth, detail to follow!

circuit switchingInternet structure

Performance: loss, delay, th h tthroughputLayering, service modelsSecurity

Introduction 1-76

SecurityHistory

CSIT 561: CSIT 561: Computer Networks“Computer Networks”

Documents

Transcript of CSIT 561: CSIT 561: Computer Networks“Computer Networks”