Advanced Program-to-Program Communication in SNA

Systems Network Architecture (SNA) defines the behavior of networks of heterogeneous, loosely coupled processors. This paper describes the development of program-to-program communication services in SNA and introduces Advanced Program-to-Program Communication (APPC), the culmination of this development. It also discusses the use of APPC in the construction of distributed services and shows that SNA with APPC and other SNA services can be thought of as a distributed operating system. S ystems Network Architecture (SNA) was announced by IBM in 1974. Since then, the original set of functions, which supported distribution of data processing between applications in a single central processor and multiple distributed cluster controllers, has been enhanced by the addition of many new functions and new products. This paper assumes some familiarity with SNA. (See References 1-14.) The first section of this paper reviews growth trends in networks and distributed processing. The second section briefly reviews the overall design of SNA. After distinguishing between the physical network of nodes connected by data links and the network of Logical Units (LUS) connected by sessions, this review emphasizes the properties of LUS, sessions, and application programs. The third section reviews applications within networks and discusses the requirements for interpro-298 GRAY ET AL gram communication that these applications place upon the architecture. The last section introduces Advanced Program-to-Program Communication (APPC) and shows how APPC meets many of these requirements. Growth trends The rapid improvements in computer and terminal function together with declining costs suggest continued large growth in applications during the rest of the 1980s. The number of installed workstations many of them intelligent-may reach twenty million during the next five years. Because they are easy to develop, small (independent) applications for these workstations are expected to be available in wide variety. Applications that can exist only in interaction with other applications and remote data will be more difficult to develop and so will be available in less variety. An important growth area is local area net-Relatively inexpensive direct connections are featured by local area networks, along with low delay and high bandwidth. The SNA design, which 0 Copyright 1983 by International Business Machines Corporation. Copying in printed form for private use is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract, but no other portions, of this paper …