2. OSI and TCP IP

8/6/2019 2. OSI and TCP IP

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ALTTC/ BB Faculty 1

TCP/IP Protocol Suite


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ALTTC/ BB Faculty 2

Objectives

What is Internet?

Comparison of TCP/IP & OSI

Data Encapsulation

TCP-IP Protocol Suite

TCP/IP Protocol Documents

TCP-IP Protocol Suite (IPv4 vs IPv6)


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ALTTC/ BB Faculty 3

What is Internet?

Internet is network of networks, withdifferent hardware/software technologies

Also known by the name TCP/IP Internet

Name TCP/IP is taken from the names ofthe one of the transport layer protocols(Transport Control Protocol) and thenetwork layer protocol (Internet Protocol)

TCP/IP is backbone of the Internet


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ALTTC/ BB Faculty 4

TCP/IP and OSI

OSI is made of seven layers.

TCP/IP protocol is made of five layers.

PHYSICAL

DATA LINK

NETWORK

TRANSPORT

APPLICATION

PHYSICAL

DATA LINK

NETWORK

TRANSPORT

SESSION

PRESENTATION

APPLICATION

OSI Model TCP/IP Model


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ALTTC/ BB Faculty 5

Frame Head Trailer

Frame

Data Encapsulation

Data

Data

Data

TCP Header

TCP SegmentUDP Header

UDP Message

TCP-UDP DataIP Header

IP Datagram

IP Header TCP-UDP Data

Application

TPT Layer

NW Layer

Data Link


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ALTTC/ BB Faculty 6

D

P

N

T

A

TCP/IP Protocol Suite..

ICMP IGMPRARPARP

FTPSMTP

TELNETHTTP

TFTPNFS

SNMPDNS

TCP UDP

IP

Protocols defined bythe underlying networks


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ALTTC/ BB Faculty 7

Applications using TCP

File Transfer Protocol (FTP) Provides the ability to upload and download files

between hosts on the network.

Simple Mail Transport Protocol (SMTP)

Provides the ability to send mail between userson the network.

TELNET Provides the ability to login into a remote host

and administer the machine. Hyper Text Transfer Protocol (HTTP)

Provides the ability to supply web pages betweena browser and the server.


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ALTTC/ BB Faculty 8

Applications using UDP

Trivial File Transfer Protocol (TFTP) Provides simplex file transfer for network booting

of devices.

Network File System (NFS)

Provides the ability for sharing directoriesbetween hosts on the network.

Simple N/w Management Protocol (SNMP) Provides the ability to supply network

management services on the network. Domain Name Service (DNS)

Provides mapping between domain name and IPaddress and vice versa.


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ALTTC/ BB Faculty 9

TCP Details

Provides application programs access to thenetwork using a reliable connection-orientedtransport layer service

TCP sends and receives data reliably using

sequence numbers and acknowledgments TCP is a byte oriented protocol i.e. every

byte in each packet is assigned a sequencenumber

Data stream handed over to TCP is called anunstructured stream

TCP divides this data stream into segmentsfor transmission to remote network


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ALTTC/ BB Faculty 10

TCP Header..

76543210765432107654321076543210

ACKNOWLEDGEMENT NUMBER

DESTINATIONPORTSOURCEPORT

OPTIONS AND PADDING

URGENT POINTERCHECKSUM

WINDOW SIZEFIN

SYN

RST

PSH

ACK

URG

HELEN

Octet +3Octet +2

SEQUENCENUMBER

Octet +1Octet +0


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TCP Header

Source & Destination Port (16 Bits) Can run number of applications using same transport by

multiplexing through port numbers

Port numbers are used to identify a unique application in amachine

65536 (0-65535) port numbers can be defined

Theoretically it is possible to run 65535 simultaneousapplications in a host

The first 1024 ports, port numbers 0-1023 known as wellknown port numbers, are assigned and are reserved for

standard applications and are controlled by IANA

The remaining ports, 1024-65535, are dynamic and canbe used freely by applications

Source port is randomly generated by the source machine


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Well known port numbers

Network Time Protocol123

File Transfer-Data20

File Transfer-Control21

Telnet23

SMTP25

Domain Name Server53

Trivial File Transfer69

WWW80

DESCRIPTIONPORT

Border Gateway Protocol179


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TCP Header

Sequence Number (32 Bits) Helps in establishing TCP connections, along with SYN bit,

called as Three Way Handshake

Helps in maintaining account of amount of data beingtransferred

Identifies where the encapsulated data fits within a datastream from the sender

Sequence number is incremented, in the system, every 4microsecond

Acknowledgement Number (32 Bits)

Helps in maintaining account of amount of data beingtransferred

Identifies the sequence number expected from the otherend of data transmission unit


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Seq/Ack numbers relation

During TCP Connection Establishment/Three way handshake

Acknowledgement Number Sent = SequenceNumber Received+1

During Data Transfer Acknowledgement Number Sent = Sequence

Number Received + Data Received in Bytes


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Three-Way-Handshake

ReceiverSender 0 1

0-Closed; 1-Listen; 2-SYN-Sent; 3-SYN-Received; 4-Established

AN-00000

000B01

SN-95426

2

AN- 95427000B11

SN-16780 3

AN-16781

000B10

SN-95427

4


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Data Transfer

AN- 95428

100B10

SN-16781

5

AN- 95427

000B11

SN-16780AN-00000

000B01

SN-95426

AN-16781

000B10

SN-95427

ReceiverSender

0 1

0-Closed; 1-Listen; 2-SYN-Sent; 3-SYN-Received; 4-Established; 5-Data Transfer

23

4

AN-16881

200B10

SN-95428

5

AN- 95628

150B10

SN-16881

5

AN-17031

250B10

SN-95628

5

AN- 95878

300B10

SN-17031

5


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Closing a TCP Connection

ReceiverSender

6-Finish; 0- Closed

0 0

6

SN - 95880

AN -17334

0B110SN - 17334

AN - 95881

0B010

WAITSN - 17334

AN - 95881

0 B110

6

SN - 95881AN -17334

0B010


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TCP Header.

Header Length (4 Bits) Sometimes called Data Offset

Indicates the length of header in 32-bit words

Identifies the beginning of data

Typical value is 5 unless there are options Flags (6 Bits)

Urgent (URG)

Acknowledgement (ACK)

Push (PSH) Reset (RST)

Synchronisation (SYN)

Finish (FIN)


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TCP Header..

Window Size (16 Bits) Indicates the size of the sliding window

Specifies the number of octets, starting with theoctet indicated by the acknowledgement

number, that the sender of the segment willaccept from its peer at the other end of theconnection before the peer must stoptransmitting and wait for an acknowledgement

A default window size is 4096 bytes Used for flow control by using Sliding window

mechanism


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Flow Control

Sender retains a copy of transmitted data until itreceives an acknowledgment from the remotenetwork.

If no acknowledgment is received, within aspecified time, the data is retransmitted by using

adaptive retransmission algorithm. TCP records the time of the transmission and sequence

number of the segment.

TCP again records the time of the acknowledgementreceived.

Using this delta, TCP builds a sample round-trip delay timeand uses this to build an average time for a packet to besent and to receive an acknowledgement

TCP will time out after a number of unsuccessfulretransmissions


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Sliding Window-Flow Control

Moves to rightwhenack is received.

Moves to rightwhen

datais sent.

Moves to right or leftto fix

the size ofthe window.

Window Size

Sentand ack

Sent but notack

Can be sent

Cant be sent


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TCP Header..

Checksum(16 Bits) Used for error detection

Covers both header and the encapsulated data

Urgent Pointer(16 Bits) Used only when urgent flag is set Points to the last octet of urgent data

Options One of the important options is MSS (Maximum

Segment Size) Informs the receiver of the largest segment

the sender is willing to accept, withoutcausing fragmentation


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TCP Header

Padding Consists of 1-3 octets, each equal to zero, to

force the length of TCP header to be in multiplesof four octets.


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UserDatagram Protocol

Provides unreliable connectionless service Transfers data without establishing a

session

Used for services that have an inbuiltreliability

Does not use end to end error checking andcorrection

Does not order the packets; may loose orduplicate a packet

Runs faster than TCP due to less overheads


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UDP Header..

DESTINATIONPORTSOURCEPORT

CHECKSUMMESSAGE LENGTH

76543210765432107654321076543210

Octet +3Octet +2Octet +1Octet +0


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UDP Header...

Source Port (16 Bits) Identifies the sending process.

Destination Port (16 Bits)

Identifies the receiving process.

Some fixed, pre-assigned port numbers used for serviceson the Internet.

7 for UDP; 69 for TFTP

Message length (16 Bits)

Indicates the size of the UDP header and its data in bytes.

Minimum size is 8, if carries no data.

Checksum (16 Bits)

Covers the UDP header and UDP data.

Optional; If not used, set to all zeros.


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Internet Protocol.

Provides best-effort or connectionlessdelivery service.

No error checking or tracking

If reliability is important, IP must be paired

with a reliable protocol like TCP Transmits blocks of data called datagrams

each of which is transported separately

Responsible for IP addressing

Datagrams may travel along different routesand may arrive out of sequence orduplicated.


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IP Header..

HEADER CHECKSUMPROTOCOLTIME TO LIVE

DESTINATION ADDRESS OF HOST

SOURCE ADDRESS OF HOST

PADDINGOPTIONS

76543210765432107654321076543210

FRAGMENT OFFSETMFDFIDENTIFICATION

TOTAL LENGTHTOSHLENVER



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IP Header

Version (4 Bits) Identifies the IP version to which the packet belongs

Header Length (4 Bits)

Indicates the length of IP header in 32 bit words.

Minimum length is 20 octets. Options may increase the size up to a maximum of 24

octets.

Type of Service (8 Bits)

Used for specifying special handling of packet.

Has two sub-fields:

Precedence

TOS


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IP Header.

0CRTDPPP

Reliability

0-Normal1-Maximise

Precedence

000-Routine001-Priority010-Immediate011-Flash100-Flash Override101-CRITIC/ECP110-Internetwork Control

111-Network Control

Delay

0-Normal1-Minimise

Throughput0-Normal

1-Maximise

Cost0-Normal

1-Minimise

Reserved:Always set to 0

0 = No TOS0000000


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IP Header..

Total Length (16 Bits) Specifies total length of the packet, including

header, in octets

Largest decimal number =216= 65535, themaximum possible size of an IP packet is 65535octets

Total length - header length = Packets datapayload

Identification (16 Bits) Each datagram is identified by a identification

number set by the source.

Normally incremented by 1 for each datagramsent.


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IP Header

Flags (3 Bits) First bit is not used.

Second bit is Dont Fragment (DF) bit

Third bit if More Fragment (MF) bit

Maximum Transmit Unit (MTU) is the size ofthe largest packet, including IP Header, thatcan be transmitted or received through adata link

Default MTU is 576 bytes, which can behandled by any network withoutfragmentation


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IP Header

Fragment Offset (13 Bits) The fragmentation occurs at the routers, if the

original packet length exceeds the MTU of a datalink

Used only in the cases when a datagram isfragmented on its way

Specifies the offset, in units of eight octets, fromthe beginning of header to the beginning of the

fragment Each fragment is marked, by router, with the

same identifier number


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Fragmentation..

172.16.2.0 172.16.3.0

MTU-1500 MTU-1500MTU-576

DataTCPIP

1500 B

DataTCPIP

512 B

Data

512 B

Data

476 B

DataTCPIP Data Data

DataTCPIP

IP IP IP

DF=0; MF=1; Offset=0 DF=0; MF=1; Offset=64 DF=0; MF=0; Offset=128


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Fragmentation

Only the receiver host reassembles thedatagram

The destination machine starts areassembly timer for about 60-120 seconds.

If not all fragments were received, thenhosts discard the packets and sends a timeexceeded ICMP message to the source

machine If a single fragment is lost during a

transmission, the entire packet must beresent


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IP Header

Time to live-TTL (8 Bits) Assigns a life to an IP datagram

Protocol (8 Bits)

Specifies the protocol that runs on the top of IP.

TCP-6; EGP-8; UDP-17; OSPF-89

Header Checksum (16 Bits)

Error detection field for IP header

As each router decrements the TTL, thechecksum is calculated by each router


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IP Header.

Source Address of Host (32 Bits) IP Address of the Originating Machine

Destination Address of Host (32 Bits)

IP Address of the Destination Machine

Options Security:

Specifies how secret the datagram is Strict Source Routing(SSR):

Gives the complete path to be followed Loose Source Routing(LSR):

Gives the list of routers not to be missed


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IP Header..

Record Route: Makes each router to append its IP address.

Time Stamp: Makes each router to append its IP address

and time stamp.

Padding

Ensures that the header ends on a 32 bitboundary by adding zeros after the option field.


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Underlying Networks Protocols

Ethernet Token Ring

FDDI Fiber Distributed Data Interface

HDLC High-level Data Link Control

Frame Relay

PPP Point-to-Point Protocol

ATM Asynchronous Transfer Mode


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Socket Connection..

Ports along with an IP address, known assocket connection, allow any application inany machine on an internet to be uniquelydefined.

Multiple applications can run simultaneouslyon a host by making use of separate socketconnection for each application.


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Socket Connection-Multiplexing

DATA

DATA

3753-53

2764-21

DATA

DATA

DATA 3753-53

2764-21DATA

A.B.C.D-E.F.G.H

A.B.C.D-E.F.G.H

A.B.C.D-E.F.G.HDATA 3753-53

2764-21DATA A.B.C.D-E.F.G.H

TRAILER

TRAILER HEADER

HEADER

D

P

N

T

DNSFTP

2764 3753

TCP UDP

IP

A.B.C.D

DNSFTP

21 53

TCP UDP

E.F.G.H

1. A.B.C.D(2764) E.F.G.H(21) 2. A.B.C.D(3753) E.F.G.H(53)


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Socket Connection-Demultiplexing

DP

N

T

DNSFTP

2764 3753

TCP UDP

IP

A.B.C.D

DNSFTP

21 53

TCP UDP

E.F.G.H

53- 3753

21- 2764

DATA

DATA

DATA 53- 3753

21- 2764DATA

E.F.G.H-A.B.C.D

E.F.G.H-A.B.C.D

DATA

DATA

E.F.G.H-A.B.C.DDATA 53- 3753

21- 2764DATA E.F.G.H-A.B.C.D

TRAILER

TRAILER HEADER

HEADER

1. A.B.C.D(2764) E.F.G.H(21) 2. A.B.C.D(3753) E.F.G.H(53)


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Internet Control Message Protocol

Internet Control Message Protocol is amechanism used by hosts and routers tosend notification of datagram problems backto the sender.

Sends error messages only to the sourceand not to intermediate routers.

Sole function is to report problems, not tocorrect them.

An important use of ICMP is echo/reply totest whether a destination is reachable andresponding.


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Echo request/reply (PING; Packet INternetGropher)

Destination unreachable

0-Network unreachable

1-Host unreachable

2-Protocol unreachable

3-Port unreachable

4-Fragment needed but DF bit is set

5-Source route failed

6-Destination network unknown


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7-Destination host unknown 8-Source host isolated

9-Communication with destination networkadministratively prohibited

10-Communication with destination hostadministratively prohibited

11-Network unreachable for type of service

12-Host unreachable for type of service

Time exceeded message format 0-TTL exceeded

1-Fragment reassembly time exceeded


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Internet Group Message Protocol

Internet Group Message Protocol providesallows for multicast to operate on aninternetwork.

Multicast is one-to-many communication.

A message sent can be simultaneously receivedby a group of hosts.

Special type of Class-D IP addresses,starting with 1110, are reserved as

multicast addresses.


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Address Resolution Protocol

Address Resolution Protocol is used totranslate 32 bits IP addresses to 48 bitsEthernet addresses.

A hosts physical address is determined by

broadcasting its IP address to all machines.

The machine with matching IP address, inbroadcast message, sends its hardwareaddress to the machine originatingbroadcast.


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ARP Operation

Request

Ignored

Request

IgnoredARP

Response

Accepted

Give me MAC address of129.1.1.4

Thats

Me

Here is my MAC address

129.1.1.1 129.1.1.4

129.1.1.2 129.1.1.3

08-00-39-00-2F-C3

08-00-10-99-AC-54

08-00-5A-21-A7-2208-00-39-00-2F-AB


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Reverse Address Resolution Protocol

Reverse Address Resolution Protocol isused to get the 32 bits Source IPaddress, knowing the 48 bits Hardwareaddress.

It is reverse of ARP, hence namedReverse Address Resolution Protocol.

A diskless workstation broadcasts RARP-

Request to find its IP Address at the timeof boot up.


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RARP Operation

Give me my IP address RARP Response

Diskless

work

station RARP

Server

08-00-39-00-2F-C3 08-00-10-99-AC-54

08-00-5A-21-A7-22

223.1.2.1

223.1.2.2

223.1.2.3

08-00-39-00-2F-AB


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IPv4 vs IPv6

Some independent protocols of version 4are part of ICMPv6.

RARP protocol is dropped from the suite.

ARP and IGMP are combined with ICMPv6.

ICMP IGMP

RARPARPIPv4

ICMPIPv6


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IPv6 Base Header

DESTINATION ADDRESS

(128 Bits)

SOURCE ADDRESS(128 Bits)

PAYLOAD (0-65535 Bytes)

(EXTENSIONHEADERS + DATA PACKETS FROMUPPERLAYERS)

HOP LIMITNEXT HEADERPAYLOAD LENGTH

FLOW LABELPRIVER

76543210765432107654321076543210



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TCP/IP Protocol Documents

TCP/IP technical documents are known asRequest For Comments (RFCs).

Once issued, RFC do not change.

Updated by new RFCs.

RFCs can be obsoleted but their numbers arenever used again.

A major source for RFCs is the InternetEngineering Task Force and are accessibleon site www.ietf.org


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2. OSI and TCP IP

Documents

Transcript of 2. OSI and TCP IP