Circuit-Switched Network Layer

  • Harold C. Folts
Part of the Applications of Communications Theory book series (ACTH)


CCITT Recommendation X.21 has been developed as “The General Purpose Interface between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for Synchronous Operation on Public Data Networks” [1], The only “general purpose” part, however, is the designation of the physical elements which include the electrical (X.26/X.27), functional (X.24), and mechanical (ISO 4903) characteristics described in Chapter 3 (Bertine). Additionally, the basic family of quiescent signals and states for the interface is specified. These provide the fundamental components of X.21 which will apply to all modes of operation in new data communications applications for circuit-switched, packet-switched, and general purpose integrated services [2].


Address Signal Network Layer Incoming Call Call Request Data Link Layer 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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  1. [1]
    CCITT Blue Books, CCITT Ninth Plenary Assembly, Vols. VIII.2 and VIII.3, November 1988, Geneva, Switzerland.Google Scholar
  2. [2]
    H. C. Folts, “Evolution toward a universal interface for data communications,” in Proceedings on International Conference of Computer Communications, Kyoto, Japan, Sep. 1978, pp. 675–680.Google Scholar
  3. [3]
    H. C. Folts, “X.21—The international interface for new synchronous data networks,” in Conference Record of the International Conference on Communications, IEEE, Vol. 1, San Francisco, June 1975, pp. 15–19.Google Scholar
  4. [4]
    H. C. Folts, ed., McGraw-Hill%’s Compilation of Data Communications Standards, New York: McGraw-Hill, Third Edition, 1986.Google Scholar

Copyright information

© Plenum Press, New York 1989

Authors and Affiliations

  • Harold C. Folts
    • 1
  1. 1.Omnicom, Inc.ViennaUSA

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