The socket API is a collection of socket calls that enable 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 API enables you to:

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

IMS™ TCP/IP provides two TCP/IP socket application program interfaces (APIs), similar to those used on UNIX systems. One interfaces to C language programs, the other to COBOL, PL/I, and System/370* assembly language programs.

• C language. Historically, TCP/IP has been associated with 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. Refer to the z/OS Communications Server: IP Sockets Application Programming Interface Guide and Reference for the C language socket calls supported by MVS™ TCP/IP.
• Sockets Extended API (COBOL, PL/I, Assembly Language). The Sockets Extended API (Sockets Extended) is for those who want to write in COBOL, PL/I, or assembly language, or who have COBOL, PL/I, or assembly language programs that need to be modified to run with TCP/IP. The Sockets Extended API enables you to do this by using CALL statements. If you are writing new TCP/IP applications in COBOL, PL/I, or assembly language, you might prefer to use the Sockets Extended API. With this interface, C language is not required. See CALL instruction application programming interface for details of this interface.