Overview of z/OS Communications Server

z/OS® Communications Server provides a set of communications protocols that support peer-to-peer connectivity functions for both local and wide-area networks, including the most popular wide-area network, the Internet. z/OS Communications Server also provides performance enhancements that can benefit a variety of TCP/IP applications.

z/OS Communications Server provides both SNA and TCP/IP protocols for z/OS. The SNA protocols are provided by VTAM® and include Subarea, Advanced Peer-to-Peer Networking, and High Performance Routing protocols. For more information about z/OS Communications Server SNA protocols, see z/OS Communications Server: SNA Network Implementation Guide.

Figure 1 shows the z/OS Communications Server TCP/IP protocol suite (also called stack), whose functions include associated applications, transport- and network-protocol layers, and connectivity and gateway functions. z/OS Communications Server contains IPv6 support. See z/OS Communications Server: IPv6 Network and Application Design Guide for more detailed information.

The z/OS Communications Server protocol suite supports two TCP/IP environments:

A native MVS™ environment in which users can exploit the popular TCP/IP protocols in MVS application environments such as batch jobs, started tasks, TSO, CICS® applications, and IMS™ applications.
A z/OS UNIX System Services environment that lets you create and use applications that conform to the POSIX or XPG4 standard (a UNIX specification).

Note: z/OS Communications Server exploits z/OS UNIX services even for traditional MVS environments and applications. Prior to using TCP/IP services, therefore, a full-function mode z/OS UNIX environment—including a Data Facility Storage Management Subsystem (DFSMSdfp), a z/OS UNIX file system, and a security product (such as Resource Access Control Facility, or RACF®)—needs to be defined and active before z/OS Communications Server can be started successfully.

Figure 1. z/OS Communications Server TCP/IP protocol suite

TCP/IP protocol suite of z/OS Communications Server with major applications

The application categories in Figure 1 do not list every application of the TCP/IP protocol suite.

z/OS Communications Server TCP/IP protocol-suite functions include the following categories: