Socket Programming: An Introduction to Sockets and Their Operations, Study notes of Communication

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Introduction to Socket Programming

CS 4450 (Spring 2018)

Vishal Shrivastav, Cornell University

What is a Socket?

• A socket is a method for accomplishing inter-process

communication (IPC)

▪ Allows one process to communicate with another process on the

same or different machine

2 P1 P Socket-1 Socket- P Socket- P Socket- Network

Where does Socket fit in the Network Stack? Application Transport Network Data Link Physical Send buffer Receive buffer

Userspace

Kernel

NIC

write() read() SOCKET open() (^) close()

Blocking and Non-blocking Sockets

• By default read() and write() operations are blocking
  • Function does not return until the operation is complete
• read() blocks until there is some data available in the

receive buffer

• When does write() block?
  • When the send buffer is full

Client-Server Model SERVER CLIENT 1^ CLIENT 2 CLIENT 3^ CLIENT 4 23.45.67.12 46.41.57. 93.35.17.14 53.35.17. 123.20.20. 1 2 1 2 1 2 1 2 1 2 3004 3005 3010 3004 3005 3204 3004 3028 80 22 Well known ports that clients connect to Port numbers assigned by OS

D: 123.20.20.10: S: 93.35.17.14: D: 93.35.17.14: S: 123.20.20.10:

Two traditional modes of communication

• Connection-oriented Communication
  • Establish a logical or physical connection before exchanging data
• Connectionless Communication
  • Start exchanging data without any prior arrangements between

endpoints

Handshake Data exchange

Client-Server Model - APIs

• Connectionless protocol (UDP-suite) socket() bind() read() write() socket() write() read() SERVER CLIENT

Stream vs Datagram

• Stream based protocols (such as TCP) work on bytes granularity
• When to stop reading? write(12 bytes) read(2 bytes) read(6 bytes) read(4 bytes) Receive buffer

Questions?

Demos