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A restructuring of X25 into HDLC

A restructuring of X25 into HDLC A major achievement of the standardization process has been the definition of a universal circuit interface (X21 or X21 bis) together with a universal transmission procedure (HDLC). This allows a large degree of compatibility between terminal equipments, regardless of configuration or communication media. X25 departs from this approach as it requires specialized DTE's that could no longer operate in conjunction with other simple DTE's using an HDLC interface. DTE's and procedures operating on private or public circuits would not be able to communicate with DTE's operating on public virtual circuits. This situation would be chaotic and detrimental to the user interest. Simple DTE's with single access have no need for an X25 interface. They can certainly establish a call using the X21 or X21 bis interface, and operate in packet mode with an HDLC procedure. In particular, DTE's operating in half-duplex mode, or in a multipoint configuration, cannot use X25. An analysis of X25 shows that its packet level is redundant with other level. Its functions could be performed in taking advantage of the facilities already present in HDLC. On the other hand X25 contains undesirable functions which should be eliminated or made user options, as they are generating incompatibilities. The proposal described in this paper has major advantages over the present X25 in providing compatibility between "real" and "virtual" circuits while using a standard HDLC interface for all DTE's. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png ACM SIGCOMM Computer Communication Review Association for Computing Machinery

A restructuring of X25 into HDLC

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Publisher
Association for Computing Machinery
Copyright
Copyright © 1977 by ACM Inc.
ISSN
0146-4833
DOI
10.1145/1024853.1024854
Publisher site
See Article on Publisher Site

Abstract

A major achievement of the standardization process has been the definition of a universal circuit interface (X21 or X21 bis) together with a universal transmission procedure (HDLC). This allows a large degree of compatibility between terminal equipments, regardless of configuration or communication media. X25 departs from this approach as it requires specialized DTE's that could no longer operate in conjunction with other simple DTE's using an HDLC interface. DTE's and procedures operating on private or public circuits would not be able to communicate with DTE's operating on public virtual circuits. This situation would be chaotic and detrimental to the user interest. Simple DTE's with single access have no need for an X25 interface. They can certainly establish a call using the X21 or X21 bis interface, and operate in packet mode with an HDLC procedure. In particular, DTE's operating in half-duplex mode, or in a multipoint configuration, cannot use X25. An analysis of X25 shows that its packet level is redundant with other level. Its functions could be performed in taking advantage of the facilities already present in HDLC. On the other hand X25 contains undesirable functions which should be eliminated or made user options, as they are generating incompatibilities. The proposal described in this paper has major advantages over the present X25 in providing compatibility between "real" and "virtual" circuits while using a standard HDLC interface for all DTE's.

Journal

ACM SIGCOMM Computer Communication Review – Association for Computing Machinery

Published: Jan 1, 1977

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