With the IMS™ TCP/IP feature, remote users can access IMS client/server applications over TCP/IP internets. It is a feature of TCP/IP Services. Figure 1 shows how IMS TCP/IP gives a variety of remote users peer-to-peer communication with IMS applications.

It is important to understand that IMS TCP/IP is primarily intended to support peer-to-peer applications, as opposed to the traditional IMS mainframe interactive applications in which the IMS system contained all programmable logic, and the remote terminal was often referred to as a "dumb" terminal. To connect a TCP/IP host to one of those traditional applications, you should first consider the use of Telnet, a function of TCP/IP Services which provides 3270 emulation. With Telnet, you can access existing 3270-style Message Format Services applications without modification. You should consider IMS TCP/IP only when developing new peer-to-peer applications in which both ends of the connection are programmable.

Figure 1. The use of TCP/IP with IMS

IMS TCP/IP provides a variant of the BSD 4.3 Socket interface, which is widely used in TCP/IP networks and is based on the UNIX system and other operating systems. The socket interface consists of a set of calls that IMS application programs can use to set up connections, send and receive data, and perform general communication control functions. The programs can be written in COBOL, PL/I, assembly language, or C.