Computer communications is one of the most rapidly developing technologies and it is a subject with which everyone in the computer systems profession should be familiar. Computer communications and networks is an introduction to communications technology and system design for practising and aspiring computer professionals. The subject is described from the computer system designer's point of view rather than from the communications engineer's viewpoint. The presentation is suitable for introductory reading as well as for reference. The emphasis is on practical, rather than theoretical, aspects and on technology which will become more important in the future. The majority of the subject matter applies to civil and military communications but some aspects which are unique to military applications have been included where considered signifi cant. Computer communications is a rapidly changing and highly complex subject. Sufficient practical knowledge of the subject is not usually gained at university or college but is generally developed over a period of several years by trial and error, attending courses, reading reference books and journals; this book attempts to simplify and speed up the process by bringing together a body of information which is otherwise distributed throughout many books and journals. The information is presented in a framework which makes a wider understanding of the subject possible. Basic knowledge of communications is assumed, a general famil iarity with computer systems is anticipated in later chapters, and, where relevant, theory is explained.
Table of Contents1 Data communication concepts and alternatives.- 1.1 Trends in computer communications and networks.- 1.2 Messages, characters, bit streams, symbols and waveforms.- 1.3 Digital/analog, serial/parallel, simplex/half-duplex/full-duplex.- 1.4 Synchronous/asynchronous.- 1.5 Parity/CRC/LRC/EDC/ARQ.- 1.6 Character/byte-count/bit-oriented data link control protocols.- 1.7 Balanced/unbalanced interfaces.- 2 Communications media.- 2.1 Introduction.- 2.2 Electrical cable.- 2.3 Fibre optic cable.- 2.4 Free-space optical links.- 2.5 Radio and microwave links.- 2.6 Satellite relay.- 3 Modems and multiplexers.- 3.1 Modulation and keying alternatives.- 3.2 Modems.- 3.3 Multiplexing alternatives.- 3.4 Multiplexers and concentrators.- 3.5 Error performance.- 4 Network topologies, switching and access control.- 4.1 Network topology and topography.- 4.2 Link switching techniques.- 4.3 Network access control.- 5 Layered network architectures.- 5.1 Introduction.- 5.2 Open Systems Interconnection reference model.- 5.3 Alternative network architectures.- 5.4 DEC Digital Network Architecture (DNA).- 5.5 IBM Systems Network Architecture (SNA).- 5.6 Comparison of DNA and SNA.- 6 Interface standards.- 6.1 Introduction.- 6.2 RS-232-C and V.24/V.28.- 6.3 RS-449, RS-422, RS-485 and RS-423.- 6.4 X.20, X.21 and X.21 bis.- 6.5 X.3, X.28, X.29.- 6.6 IEEE 488 (IEC 625).- 7 Local area networks.- 7.1 Local communication alternatives.- 7.2 Broadband local area networks.- 7.3 IEEE 802.2 logical link control.- 7.4 IEEE 802.3 CSMA/CD LAN.- 7.5 IEEE 802.4 token bus LAN.- 7.6 IEEE 802.5 token ring LAN.- 7.7 ANSI FDDI dual fibre optic ring.- 7.8 MIL-STD-1553 B avionic data bus.- 8 Wide area network standards.- 8.1 Long-distance communication alternatives.- 8.2 BISYNC (BSC) character-controlled protocol.- 8.3 DDCMP character-count protocol.- 8.4 SDLC bit-oriented protocol.- 8.5 HDLC bit-oriented protocol.- 8.6 CCITTX.25.- 8.7 Protocols for mobile radio links.- 8.8 Videotex (viewdata).- 9 Performance prediction.- 9.1 Introduction.- 9.2 Link performance.- 9.3 Wide area network performance prediction.- 9.4 Local area network performance prediction.- 9.5 Network reliability and availability prediction.- 10 Computing and software issues.- 10.1 Introduction.- 10.2 Distributed data processing.- 10.3 Network software.- 10.4 Distributed databases.- 10.5 PC-to-mainframe links.- 10.6 CCITTX.400.- 10.7 Data compression.- 11 Threats to communications security.- 11.1 Introduction.- 11.2 Passive attacks.- 11.3 Active attacks.- 11.4 System penetration ploys against dial-up systems.- 11.5 Countermeasures.- 11.6 Port protection.- 11.7 Encryption.- 11.8 Trusted computers and networks.- 11.9 Security in the open systems architecture.- 12 Network implementation.- 12.1 Requirements analysis and architectural design.- 12.2 Implementation options.- 12.3 System integration.- 12.4 Network protection and reconfiguration.- 12.5 Network management and testing.- Appendix: Data communications standards.- References.