networking chapter vii

Compiled by: Jayakumar BalasubramanianWeb: http://www.jwritings.com

Email: b.jayakumar@gmail.com

Transmission Control Protocol (TCP)

The TCP service modelUnderlying media is ‘unreliable’An ‘end-to-end’ connection oriented, reliable

protocol is requiredTCP functionalities:

Service mapping based on port numbers Congestion control Connection establishment and termination Acknowledgement Timeout and re-transmission

Transport addressing - Ports

Ports and services

192.18.22.13

Port 80 25 23

Application WWW E-mail Telnet

Ports and services

How does TCP achieve all this?The TCP maintains a method called as

‘three-way-handshake’ for connection establishment

The connection termination also happens in a pre-defined way

Since both ends know each other, the ‘connectedness’ comes is achieved

Various flag fields are used: ACK, SYN, RST, FIN

Connection establishment

Connection termination

UDP header

The RAW sockets

How to program RAW sockets?Use simple socket() call with some different

parametersCreating a RAW socket:

TCP protocol: IPPROTO_TCP UCP protocol: IPPROTO_UDP

socket (AF_INET,SOCK_DGRAM,IPPROTO_IP)

Sending and receiving data: Send: write() system call Receive: read() system call

Can be used for any packet capturing and analyzing protocol

Web : http://www.jwritings.comEmail: b.jayakumar@gmail.com