The socket call interface provides a set of programming calls that can be used in an IMS™ message processing program to conduct a conversation with a peer program in another TCP/IP processor. The interface is derived from BSD 4.3 socket, a commonly used communications programming interface in the TCP/IP environment. Socket calls include connection, initiation, and termination functions, and basic read/write communication. The MVS™ TCP/IP socket call interface makes it possible to issue socket calls from programs written in COBOL, PL/I, and assembly language.

The IMS socket calls are a subset of the TCP/IP socket calls. They are designed to be used in programs written in other than C language; hence the term Sockets Extended.