This section describes the socket communication model on the Internet network. A socket 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 handle 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 program 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. B
