BKINTDCM.RVW 930803 CBM Books 101 Witmer Road PO Box 446 Horsham, PA 19044 215-957-4265 Fax: 215-957-1050 76702.1565@compuserve.com books@propress.com "Introduction to data communications", Gelber, 1991, U$39 For no very good reason, I was looking forward to reading this book. Four chapters into it, I was beginning to wonder if any purpose would be served by reviewing it. Having finished it, I recommend the bulk of the work as a comprehensive and lucid introduction to the subject, though primarily practical only if you are dealing with IBM mainframes and networks. The intelligent reader, even with no background, should come away with a clear grasp of the concepts involved. Gelber admits, in the preface, that most of the examples he is using are drawn >from the IBM (mainframe, one assumes) world. Initially, this bias is clearly evident, even though he states that he is trying to write a text, or just a book suitable for "anyone who desires a comprehensive, basic introduction to data communications". From the very first chapter, the philosophy, mindset and even diagrams of IBM are evident in the work. The introductory chapter will likely scare most away from the work. The progression is disjointed and abrupt, and the illustrations make no sense unless you already know the topic. (The one "basic" illustration purports to show a relation between analog and digital signals: in fact, it simply shows, as usual, that no art department can generate a sine wave.) Chapter two, supposedly explaining network planning, again assumes that "network capacity" requirements are known, without any thought to explain how these might be determined. Questions such as CPU size requirements and the need for "RJE" might have been lifted wholesale from an IBM sales manual. There are "review questions" at the end of every chapter. Many are merely silly ("Data communications had its beginnings when Samuel Morse did what?"), while others seem to misinterpret basic concepts of the field. (The question, "What is the predominant transmission method used today for data communications?" is answered with "Analog transmission". In fact, since we haven't yet managed to harness quantum mechanics for computing, no truly "digital" communications device exists since the *world* is analog.) Chapters three and four purport to cover "Communications Software" and "Application Development". Again, very few concepts are detailed here, and those which are deal with strictly IBM terminology. (Question 3.5: "What does the term "conversational mode processing describe?" Book answer: "The process of establishing and maintaining a communications session until the user terminates the connection." Can you say "interactive processing"? Can you say "real time"? I knew you could.) Part three, however, almost seems to be another book. Chapter five deals clearly with bandwidth, duplex and synchronous carriers, and the types of (data transmission only) services are lucidly described in chapter six. Chapter seven discusses modulation of signals and coding, and although the sine waves are no better, the explanations are great. (I notice that Gelber, in common with all other data communications instructors, "chickens out" when the topic turns to "Trellis Coded Modulation".) Part four, with chapters covering hardware links (the "physical layer", mostly cabling), other data communications hardware (multiplexers, bridges and the like), modems and hardware and interfaces (mostly plugs) carries on in the same high standard. While the ordering and organization of the material could be improved, the descriptions and tutelary content are first rate. Part five, covering regulation and standards, network configurations, network architectures and protocols is, again, excellent, as is part six, dealing with LANs, their repair and management. The book ends with a brief look at the future. This seems to be almost required of technical works today, but Gelber keeps it mercifully short and generic. The first two parts (and four chapters) definitely need to be replaced with a more realistic introduction. While the remaining material in the book is useful, clear, accurate and of a high standard, it could also use some planning and reorganization, so that the reader knows that there is a design at work. As it is, I would recommend that you buy this book, rip out the first four chapters, and staple in your own study guide to the remaining material. It is well worth the effort. copyright Robert M. Slade, 1994 BKINTDCM.RVW 930803 ====================== DECUS Canada Communications, Desktop, Education and Security group newsletters Editor and/or reviewer ROBERTS@decus.ca, RSlade@sfu.ca, Rob Slade at 1:153/733 Author "Robert Slade's Guide to Computer Viruses" (Oct. '94) Springer-Verlag