Chirag's Blog: What is Socket | How Socket Works | Need of Socket | What is Socket address | Types of Socket | Stream Socket

What is socket?

A socket is one endpoint of a two-way communication link between two programs running on the network. The application creates a socket. Socket is an interface between application layer and transport layer.

It is an interface (a “door”) into which an application process can both send and receive message to/from another application process (remote/local application process). Socket is also referred as the application programmer’s interface (API) between the application and the network.

Need of Socket

When we desire a communication between two applications possibly running on different machines, we need sockets. Requirement of socket is to build any Network Application i.e., Web browsers, FTP etc…

How Socket Works?

There are two different programs running on two different machines in network. Client program wants to communicate with server program. Client select any free port from client machine and send data to server process. Server select port which is bind with particular server process. That port is called agreed or specific port. After that logical connection is created between client and server. Server received client process at agreed/specific port. Then communication is started between server and client.

What is Socket address?

Socket is combination of IP address and Port number. IP address is used for host-to-host communication in network. IP address is assigned by network layer. Port number is used for process-to-process communication in network. Port number is assigned by transport layers protocol.

How process can identify using socket?

Let’s take one example, there is one Server host and Client host in above diagram. There are two different servers are configured on server host. Client send a request message to server. Request message is received from port number 80. At server-side Web server is bind with port number 80. So, Sever OS forward that request message to Web server. Process is identify based on port address. Port address is already assigned in unique socket address.

On which layer socket is execute in TCP/IP Model?

Socket is executed at transport layer in TCP/IP as well as in OSI model. Socket address is combination of IP address and port number. Port number is assigned by transport layer protocol either TCP or UDP. Port address is used for process-to-process communication in network.

Types of Sockets

There are two types of sockets: Stream Socket and Datagram Socket.

Stream Socket

Stream socket is also called connection- oriented socket. It provides reliable, connected networking service. Error free; no out- of- order packets (uses TCP). Applications of Stream Sockets are telnet/SSH, http, https and many more.

Datagram Socket

Datagram socket is also known as Connectionless socket. It provides unreliable, best- effort networking service Packets may be lost; may arrive out of order (uses UDP). Application of Datagram Sockets are streaming audio/ video (real player) and many more.

Raw Socket, Sequenced packet Socket etc.

To learn more about Introduction of Socket, Click here