The socket API communication functions

The socket API is a collection of socket calls that enables you to perform the following primary communication functions between application programs:

Set up and establish connections to other users on the network
Send and receive data to and from other users
Close down connections

In addition to these basic functions, the APIs enable you to:

Interrogate the network system to get names and status of relevant resources
Perform system and control functions as required

CICS® TCP/IP provides three TCP/IP socket application program interfaces (APIs), similar to those used on UNIX systems. One interfaces to C language programs, the other two to COBOL, PL/I, and assembler language programs.

C language. Historically, TCP/IP has been linked to the C language and the UNIX operating system. Textbook descriptions of socket calls are usually given in C, and most socket programmers are familiar with the C interface to TCP/IP. For these reasons, TCP/IP Services includes a C language API. If you are writing new TCP/IP applications and are familiar with C language programming, you might prefer to use this interface. See C language application programming for the sockets calls provided by TCP/IP Services.
Sockets Extended API (COBOL, PL/I, assembler language). The Sockets Extended API is for those who want to write in COBOL, PL/I, or assembler language, or who have COBOL, PL/I, or assembler language programs that need to be modified to run with TCP/IP. If you are writing new TCP/IP applications in COBOL, PL/I, or assembler language, you might prefer to use the Sockets Extended API. See Sockets extended API for details of this interface.
Version 2.2.1 (COBOL, PL/I, assembler language). This is the API that was offered to users of the original release of CICS TCP/IP. It is similar in use to the Sockets Extended API. The Version 2.2.1 API is available for those who want to maintain Version 2.2.1 programs. This interface is described in Original COBOL application programming interface (EZACICAL).