RFC 1328 (rfc1328) - Page 1 of 5

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Network Working Group                                S. Hardcastle-Kille
Request for Comments: 1328                     University College London
                                                                May 1992


                     X.400 1988 to 1984 downgrading

Status of this Memo

   This RFC specifies an IAB standards track protocol for the Internet
   community, and requests discussion and suggestions for improvements.
   Please refer to the current edition of the "IAB Official Protocol
   Standards" for the standardization state and status of this protocol.
   Distribution of this memo is unlimited.

Abstract

   This document considers issues of downgrading from X.400(1988) to
   X.400(1984) [MHS88a, MHS84].  Annexe B of X.419 specifies some
   downgrading rules [MHS88b], but these are not sufficient for
   provision of service in an environment containing both 1984 and 1988
   components.  This document defines a number of extensions to this
   annexe.

   This specification is not tutorial.  COSINE Study 8.2 by J.A.I.
   Craigie gives a useful overview [Cra88].

1.  The need to Downgrade

   It is expected that X.400(1988) systems will be extensively deployed,
   whilst there is still substantial use of X.400(1984).  If 1988
   features are to be used, it it important for there to be a clear
   approach to downgrading.  This document specifies an approach to
   downgrading for the Internet and COSINE communities.  As 1988 is a
   strict superset of 1984, the mapping is a one-way problem.

2.  Avoiding Downgrading

   Perhaps the most important consideration is to configure systems so
   as to minimise the need for downgrading.  Use of 1984 systems to
   interconnect 1988 systems should be strenuously avoided.

   In practice, many of the downgrading issues will be avoided.  When a
   1988 originator sends to a 1984 recipient, 1988 specific features
   will not be used as they will not work!  For distribution lists with
   1984 and 1988 recipients, messages will tend to be "lowest common
   denominator".




Hardcastle-Kille
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