Critique of X.25 (RFC0874)
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2019-Feb-14
Internet Society Requests For Comment (RFCs)
This RFC is an analysis of X.25 pointing out some problems in the conceptual model, particularly the conflict between the interface aspects and the end-to-end aspects. The memo also touches on security, and implementation issues. Originally published as M82-50 by the MITRE Corporation, Bedford, Massachusetts.
< INC-PROJECT, MAP-CRITIQUE.NLS.10, >, 12-Aug-83 11:46 AMW ;;;;
RFC 874 September 1982 M82-50
A CRITIQUE OF X.25
M.A. PADLIPSKY THE MITRE CORPORATION Bedford, Massachusetts
The widely touted network interface protocol, "X.25", and its attendant conceptual framework, the International Standards Organization’s Reference Model for Open System Interconnection (ISORM), are analyzed and found wanting. The paper is a companion piece to M82-48, and M82-51.
A CRITIQUE OF X.25
M. A. Padlipsky
According to some sources, the International Standards Organization’s (ISO) "Open System Interconnection" (OSI) effort has adopted the International Consultative Committee on Telephony and Telegraphy (CCITT) developed X.25 protocol(s) as its Levels 1-3. ("Loose constructionists" of the ISORM would hold that X.25 is a mechanization of L1-L3 rather than the mechanization, and at least one British source holds that "we in the U.K. don’t believe that ISO have adopted X.25.") In the U.S. Government arena, where the author spends much of his time, the Government Accounting Office (GAO) has suggested that the Department of Defense (DoD) ought to consider adopting "X.25 networks," apparently in preference to networks based on protocols developed by the DoD-sponsored intercomputer networking research community. That intercomputer networking research community in turn has, with a few recent exceptions, adhered to its commitment to the Oral Tradition and not taken up the cudgels against X.25 in the open literature, even though X.25 is an object of considerable scorn in personal communications.
Although the DoD Protocol Standards Technical Panel has begun to evolve a "Reference Model" different from ISO’s for reasons which will be touched on below, there seems to be a need to address the deficiencies of X.25 on their own demerits as soon as possible. Without pretending to completeness*, this paper will attempt to do just that.
The overall intent is to deal with X.25 in the abstract; because of who pays the bills, though, a necessary preliminary is to at least sketch the broad reasons why the DoD in particular should not
________________ * Various versions of X.25 and ISO documentation were employed; one incompleteness of note, however, is that no attempt has been made to do proper bibliographic citation. Another incompleteness lies in the area of "tutoriality"; that is, appropriate prior knowledge is assumed on the part of the reader. (The author apologizes for the omissions but hasn’t the time or the energy to be overly scholarly. Reference  might be of use to the reader who feels slighted.)
RFC 874 September 1982
employ intercomputer networks which base their protocol suites on the ISO Reference Model (ISORM) with X.25 as Levels 1-3. (Note that this is a different formulation from "use communications subnetworks which present an X.25 interface.") Very briefly, the DoD has concerns with "survivability," reliability, security, investment...