1

Introduction to TCP/IP

Jaimon Jacob

Asst. Professor in CS

2

OSI and Protocol Stack OSI: Open Systems Interconnect

OSI Model TCP/IP Hierarchy Protocols

7th

Application Layer

6th

Presentation Layer

5th

Session Layer

4th

Transport Layer

3rd

Network Layer

2nd

Link Layer

1st

Physical Layer

Application Layer

Transport Layer

Network Layer

Link Layer

Link Layer : includes device driver and network interface cardNetwork Layer : handles the movement of packets, i.e. RoutingTransport Layer : provides a reliable flow of data between two hostsApplication Layer : handles the details of the particular application

3

Packet Encapsulation

The data is sent down the protocol stack

Each layer adds to the data by prepending headers

22Bytes 20Bytes 20Bytes 4Bytes

64 to 1500 Bytes

4

Ethernet

Computer Computer communication on same network

Each device has unique MAC address (48-bit)

example: 00-C0-4F-48-47-93

Ethernet Packet:

Dest.address

Data CRCSourceaddress

Type

MAC: Media Access Control

6bytes 6bytes 2bytes

Preamble

8bytes 64 - 1500bytes 4bytes

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ARP : Address Resolution Protocol

ARP provides mapping

32bit IP address 48bit MAC address

128.97.89.153 00-C0-4F-48-47-93

ARP cache

maintains the recent mappings from IP addresses to MAC addresses

Protocol

1. ARP request broadcast on Ethernet

2. Destination host ARP layer responds

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IP: Internet Protocol

Unreliable connectionless datagram delivery service

Responsible for routing of data through intermediate networks and computers

IP header:

1 :ICMP6 :TCP17 :UDP

118901

11112345

11116789

22220123

22224567

223389010123 4567

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IP Routing

Routing Table

Destination IP address

IP address of a next-hop router

Flags

Network interface specification

Application

Transport

Network

Link

Application

Transport

Network

Link

Network

Link

Source Destination

Router

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ICMP : Internet Control Message Protocol

Used to report problems with delivery of IP Datagrams within an IP network

Used by Ping, Tracerout commands

Types and Codes

Echo Request (type=8, code=0)

Echo Reply(type=0, code=0)

Destination Unreachable(type=3, code=0)

Time Exceeded(type=11, code=0) : Time-to-Live =0

ICMP Message

ICMP Data

ICMPHeader

IPHeader

4bytes20bytes

Type Code Checksum

1byte 1byte 2bytes

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TCP : Transmission Control Protocol

Connection-Oriented, Reliable, Byte Stream Service

Protocol

1. Set up connection

2. Transfer data

3. Close connection

0 1 2 3 4 5 6 7 8 9 1

0

1

1

1

2

1

3

1

4

1

5

1

6

1

7

1

8

1

9

2

0

2

1

2

2

2

3

2

4

2

5

2

6

2

7

2

8

2

9

3

0

3

1

Source Port Destination Port

Sequence Number

Acknowledgement Number

Data

Offset

- - - - Window

Checksum Urgent Pointer

Options (0 to 10 Words of 32 Bits)

TCP Payload

TCP Header Format

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TCP : State Diagram

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TCP : Connection

HostClient

Send SYN seq=x

Receive SYN+ACK segment

Send ACK y+1

Receive SYN segmentSend SYN seq=y, ACK x+1

Receive ACK segment

HostClient

Send FIN seq=x

Receive FIN + ACK segmentSend ACK y+1

Receive FIN segmentSend ACK x+1

Receive ACK segment

Establishing a TCP Connection Closing a TCP Connection

Receive ACK segment

Send FIN seq=y, ACK x+1

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TCP : Data transfer

HostClient

Send Packet 1Start Timer

Retransmit Packet1Start Timer

Packet should arrive ACK should be sent

ACK would normallyArrive at this time

Receive Packet 1Send AXK 1

Time Expires

Receive ACK 1Cancel Timer

Packet LostTimer

Timer

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HTTP : Hyper Text Transfer Protocol

Stateless Transaction Protocol

Each transaction creates a new connection

Steps in Transaction

1. Establish connection

2. Request

Method

3. Response

Response Code

4. Close connection

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HTTP

Common Request Methods

GET, PUT, POST

Response Categories

Informational :100

Successful :200

Redirection :300

Client Error :400 (eg. 404 Not found)

Server Error :500

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Example: Access www.ee.ucla.edu

Http requestGET http://www.ee.ucla.edu

Http response200

Initiate connection (hdshk)Package data (add TCP header)send http request packet

Assemble response(break into several packets)Send http response packets

send data to next hop

Appl

HTTP

Transp

TCP

NetIP

Linkethernet

Close connection (hdshk)

Relay data

Client Server

Router(s)

NetIP

Linkethernet

Appl

HTTP

Transp

TCP

NetIP

Linkethernet

ARP to provide IP/MAC translation

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References

TCP/IP Illustrated, Volume 1 The Protocols

by W. Richard Stevens (http://yenigul.net/tcpip)

Internet Working with TCP/IP Volume 1

by Douglas E. Comer

Sams Teach Yourself TCP/IP in 24 Hours

by Joe Casad. Published by Sams. (http://www.informit.com)

http://yenigul.net/tcpiphttp://www.informit.com/