The book is intended to be a tutorial on the concepts behind the structure and inner workings of systems network architecture (SNA). Meijer’s description of SNA is not truly complete, but he does explain the most important aspects of SNA. He starts with a brief history of SNA, explaining the purposes of the various releases and describing the enhancements that the later releases provide. He also presents a general overview of the SNA architecture and thoroughly explains the fundamental rule of SNA: no communication is allowed to occur unless a session exists between the communicating entities. The book delves into how sessions are set up, how they are identified, and what half-sessions and parallel sessions are. It also explains the various physical unit types.

Meijer gives an elaborate discussion of IBM’s synchronous data link control (SDLC) and compares it with the high-level data link control (HDLC) of the OSI architecture. He presents the operation of the SDLC loop, which has not been defined for the HDLC, and discusses the relationship of SDLC to IBM’s token ring in some detail.

The discussion of the path control layer explains how SNA networks do addressing. The author describes node types and path control functions together with the explicit routes (both forward and reverse paths) that SNA defines between nodes. He discusses the transmission control layer in sufficient detail, presents the components that make up the layer and describes their functions, and also discusses the data flow control layer in terms of flow control protocols and data flow control functions.

The author follows the overview of the SNA layers and their functions with newer material that relates the logical unit (LU) types and the interconnection of SNA networks. He singles out LU 6.2 for detailed discussion because it is IBM’s selected LU type for future use and uses two examples to illustrate his explanation of the operation of LU 6.2. One consists of a simple transaction in which data flows in only one direction, and the other has data flow in both directions. The discussion of SNA interconnection is elaborate and presents seven SNA gateway configurations. It also presents the basic functions that the gateway performs in order to maintain the autonomy and independence of the interconnected networks.

The chapter on related architectures discusses only architectures that build on top of SNA’s communications capabilities; it does not make any mention of network architectures from other companies. It briefly compares SNA with the OSI reference model in terms of how IBM provides support for those layers of the OSI reference model that are above the X.25 packet level.

The book presents an excellent overview of the SNA architecture. The style is simple and easy to decipher, although the few typographical errors could have been avoided. This work will serve as an excellent text for teaching the SNA architecture; the only knowledge needed to comprehend the material is a background in basic data communications concepts. The book includes a list of the acronyms used, and the index covers the important terms. The list of references is also substantial but, as one might expect, it consists largely of IBM information papers and documents.