int socket(int domain, int type, int protocol);

The socket created is one end point of a communication channel. The domain parameter specifies the address family, the type parameter specifies the type of communication to be used with this socket, and protocol specifies the protocol to be employed.

int bind(int socket, const struct sockaddr *address, size_t address_len);

The bind system call assigns the address specified in the parameter, address, to the unnamed
socket associated with the file descriptor socket. The length of the address structure is passed as address_len.

int listen(int socket, int backlog);

A Linux system may limit the maximum number of pending connections that may be held in a queue.Subject to this maximum, listen sets the queue length to backlog. Incoming connections up to this queue length are held pending on the socket; further connections will be refused and the client’s connection will fail.

int accept(int socket, struct sockaddr *address, size_t *address_len);

The accept system call returns when a client program attempts to connect to the socket specified by the parameter socket. The client is the first pending connection from that socket’s queue. The accept function creates a new socket to communicate with the client and returns its descriptor.

int connect(int socket, const struct sockaddr *address, size_t address_len);

The socket specified by the parameter socket is connected to the server socket specified by the parameter address, which is of length address_len. The socket must be a valid file descriptor obtained by a call to socket