The document summarizes key aspects of TCP including its connection-oriented and reliable service model, how it establishes and terminates connections through a three-way handshake and defined process, and how ports are used to map services like HTTP, email, and telnet to applications. It also briefly outlines how to program raw sockets in order to send and receive packets for any protocol.

1. Compiled by: Jayakumar Balasubramanian Web: http://www.jwritings.com Email: [email_address]

2. Transmission Control Protocol (TCP)

3. The TCP service model Underlying media is ‘unreliable’ An ‘end-to-end’ connection oriented, reliable protocol is required TCP functionalities: Service mapping based on port numbers Congestion control Connection establishment and termination Acknowledgement Timeout and re-transmission

4. Transport addressing - Ports

5. Ports and services 192.18.22.13 Port 80 25 23 Application WWW E-mail Telnet

6. Ports and services

7. 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

8. Connection establishment

9. Connection termination

10. UDP header

11. The RAW sockets

12. How to program RAW sockets? Use simple socket() call with some different parameters Creating 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

13. Web : http://www.jwritings.com Email: [email_address]