• It is a logical connecting point between a server and a client on a network.
• Each socket is given an identification number called port number.
• Port number takes 2 bytes and can be from 0 to 65,535.
• To establish a communication between a server and a client is called as Socket programming.
• We will use a new port number for each new socket.
• That means every new service on the net should be assigned a new port number.

The following table represents some port numbers which are already used by applications running in our system.

Fig :

• • When a socket at server side is called server socket which is created using ServerSocket class.
• • Similarly a socket at client side is called as Socket which is created using Socket class.
• • Both ServerSocket and Socket class are available in java.net package.