Transport layer & Socket

Multiplexing and Demultiplexing

 

 

• Multiplexing at sender: sending data from its own multiple applications through network
• Demultiplexing at receiver: delivering data packets to their appropriate receivers among its own multiple applications
• Theses are provided by the transport layer.

Port number

 

• different applications are assigned different port numbers
• transport layer segments have fields for source port and destination port numbers. so that each data goes to its destination.
• However, the transport layer must be instructed by the application which process on which host should be the destination.
• the mechanism of instructing transport layer is by socket

 

Socket

 

• is provided as the form of APIs by OS
• It is tiring for a programmer to develop all the network system on which her software sends and receives data.
• So normally OS provides APIs between transport layer and application layer.
• API stands for Application Program Interface which is function with which application can call to send data
• you can provide data and url in this API function.
• The set of these API functions is socket.
• Example of Simple Socket program
•  



• [server]
  • 1) import socket
  • 2) ss.socket: create a server socket
  • 3) ss.bind: assign IP Address and port number to the socket
  • 4) ss.accept: accept connection request from client
  • 5) ss.recv: receive data
• [client]
  • 1) cs.socket: establish the connection/ create a client socket 
  • 2) cs.connect: request connection to ‘localhost’ of which port number is 8089
  • 3) cs.send: send data 

 

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