Network socket

A network socket is an internal endpoint for sending or receiving data at a single node in a computer network. Concretely, it is a representation of this endpoint in the networking software (), such as an entry in a table (listing communication protocol, destination, status, etc.), and is a form of system resource.

The term "socket" is by analogy with physical female connectors, communication between two nodes through a channel being visualized as a cable with two male connectors plugging into sockets at each node. Similarly, the term "port" (another term for a female connector) is used for external endpoints at a node, and the term "socket" is also used for an internal endpoint of local inter-process communication (IPC) (not over a network). However, the analogy is strained, as network communication need not be one-to-one or have a channel.

A socket can be referred to by a process (a running computer program) by using a socket descriptor, a type of handle (abstract reference, often represented internally as an integer). A process first requests that the protocol stack create a socket, and the stack returns a descriptor to the process so it can identify the socket. The process then passes the descriptor back to the protocol stack when it wishes to send or receive data using this socket.

Sockets are local (specific to one node): they are local resources and cannot be referred to directly by other nodes, unlike ports. Further, sockets are not necessarily associated with a persistent connection (channel) for communication between two nodes, nor is there necessarily some single other endpoint. For example, a datagram socket can be used for connectionless communication, and a multicast socket can be used to send to multiple nodes, or an address range where there may or may not be any nodes to receive data. However, in practice for internet communication, sockets generally have associated addresses and often have a connection.

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