A network architecture is a set of rules and procedures that govern the connection of the various network components, the interaction among them, the data formats adopted, the protocols, and the logical structure of their functions. These rules provide a framework for combining hardware and software components into an efficient, integrated communication network of data processing systems. Systems Network Architecture (SNA), first introduced in 1974 by IBM, is based on a hierarchical network architecture. SNA is an end-user–oriented architecture, in contrast to X.25, which is communication-oriented. Over the years, and through five versions, SNA has evolved into an extremely complex design standard. Version 3 provided for terminals to access databases and programs residing on more than one host machine through virtual telecommunications access methods (VTAM) and network control program (NCP) software.

This book is a sequel to the authors’ previous book [1]. It is intended mostly for practicing VTAM/NCP designers working with medium to large IBM mainframes, and not for a novice in the field. The book is divided into four parts. Part 1 deals with communications hardware such as the IBM 3174 Establishment Controller and IBM 3745 Communications Controller, types of hardware, their modes of operation, and the ways of configuring them. Part 2 deals with the implementation of VTAM in a multidomain situation in which two or more VTAM domains may communicate with each other. Part 3 is concerned with the management of SNA and with performance and tuning of networks. Part 4 is titled “New Connectivity Issues.” It includes chapters on low entry networking and token-ring LAN networking.

True to the authors’ disclaimers, the book does not deal with the theoretical aspects of SNA. Instead, it is an implementor’s guide, replete with helpful code fragments, macros, set-up statements, and so on. The authors provide catchy diagrams, rules of thumb for configuring the network components, and formulae for determining working parameters. Each chapter ends with a summary. IBM manuals are mines of information on the topic; like any mine, they are useful only if one knows what to look for and where. The authors have done a good job of collecting all the relevant materials from these labyrinths and organizing them in one volume.

Many industries are reorienting their information processing strategies to rely on networks more and more. One can realistically expect such new opportunities to follow the open systems interconnection (OSI) route, rather than adopting a single vendor architecture, such as SNA. Although SNA and OSI are designed and implemented differently, SNA is a total systems architecture with provisions for host CPUs, device controllers and terminals, and network management. OSI is a set of standards for peer-to-peer communication among independent, self-sustaining systems that rely on common carrier facilities like X.25. With the increasing degree of intelligence being built into personal computers, many small devices are being classified as standalone systems, which are capable of communicating with other systems. SNA and OSI can therefore be viewed as complementary architectures.

Quite a few vendors other than IBM have designed their products to be compatible with SNA. When full functional compatibility is realized, SNA systems will have what may be termed an OSI connection point, through which an SNA system could be interfaced with another system via OSI standards. It is likely that SNA and OSI will experience an almost parallel growth in popularity and usage. One can expect a large readership for authoritative books on SNA, such as this volume.