The IP CICS® socket API and the IBM® supplied listener is IPv4 and IPv6 enabled.

CICS Transaction Server (CICS TS) is an online transaction processing system. Application programs using CICS can handle large numbers of data transactions from large networks of computers and terminals.

Communication throughout these networks has often been based on the Systems Network Architecture (SNA) family of protocols. CICS TCP/IP offers CICS users an alternative to SNA, the TCP/IP family of protocols for those users whose native communications protocol is TCP/IP.

CICS TCP/IP allows remote users to access CICS client/server applications over TCP/IP Internets. Figure 1 shows how these two products give remote users peer-to-peer communication with CICS applications.

It is important to understand that CICS TCP/IP is primarily intended to support peer-to-peer applications, as opposed to the traditional CICS mainframe interactive applications in which the CICS system contained all program 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 using Telnet. With Telnet, you should be able to access existing 3270-style basic mapping support (BMS) applications without modification and without the need for additional programming. Use CICS TCP/IP when you are developing new peer-to-peer applications in which both ends of the connection are programmable.

Figure 1. The use of CICS sockets

CICS TCP/IP provides a variant of the Berkeley Software Distribution 4.3 sockets 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 your CICS application programs can use to set up connections, send and receive data, and perform general communications control functions. The programs can be written in COBOL, PL/I, assembler language, or the C language.