The server must first obtain a socket 1. This socket provides an end-point to which clients can connect.

A socket is actually an index into a table of connections in the TCP/IP address space, so TCP/IP usually assigns socket numbers in ascending order. In COBOL, the programmer uses the SOCKET call to obtain a new socket.

The socket function specifies the address family (AF_INET), the type of socket (STREAM), and the particular networking protocol (PROTO) to use. (When PROTO is set to zero, the TCP/IP address space automatically uses the appropriate protocol for the specified socket type). Upon return, the newly allocated socket's descriptor is returned in RETCODE.