What Is a Socket?

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∟What Is a Socket?

This section describes what is a socket - An concept represents one end-point of a two-way communication link between two programs running on the Internet network.

Socket: An concept represents one end-point of a two-way communication link between two programs running on the Internet network.

Internet Address: A unique number to identify each computer system on the Internet.

Port: A number representing an entry point of on a computer system on the Internet, where a two-way communication link can be established.

Local System: The computer system at this end of a two-way communication link.

Remote System: The computer system at the other end of a two-way communication link.

A two-way communication link on the Internet involves:

Two computer systems, each has its own Internet address.
A port number on each computer system that is used only by this communication link.
An application program on each computer system that uses this communication link.
A socket object created in the application program that represents this communication link.
The application program can use the socket as a logical input or output device to receive or send data from or to the application program running at the other end of the communication link.
The application program can also query the socket for information about the communication link, like: The Internet address and port number at this end of the communication link; The Internet address and port number at the other end of the communication link.

The following diagram illustrates how an application program can use a socket to talk with other application programs running on another computer system through a two-way communication link on the Internet:

Computer System I                            Computer System II

       i/o       |Address a|    Internet    |Address b|       i/o
App. A<--->Socket|Port 1   |<-------------->|   Port 2|Socket<--->App. X