- Process to process delivery (transport layer communication) needs two identifiers, one is IP address and the other is port number at each end to make a connection.
- Socket address is the combinations of IP address and port number as shown in the figure.
- The client socket address defines the client process uniquely whereas the server socket address defines the server process uniquely.
- A transport layer protocol requires the client socket address as well as the server socket address. These two addresses contain four pieces.
- These four pieces go into the IP header and the transport layer protocol header.
- The IP header contains the IP addresses while the UDP and TCP headers contain the port numbers.
- A transport-layer protocol in the TCP suite needs both the IP address and the port number, at each end, to make a connection. The combination of an IP address and a port number is called a socket address.
- The client socket address defines the client process uniquely just as the server socket address defines the server process uniquely as shown in Figure.
- To use the services of transport layer in the Internet, we need a pair of socket addresses: the client socket address and the server socket address.
- These four pieces of information are part of the network-layer packet header and the transport-layer packet header. The first header contains the IP addresses; the second header contains the port numbers.
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