RFC 1465 (rfc1465) - Page 3 of 31

Routing Coordination for X

RFC 1465        Routing Coordination for X.400 Services         May 1993


      single entry point (and therefore a single point of failure).
      This document proposes to use the term RELAY-MTA, reflecting more
      clearly the functionality of the MTA.

   COSINE-MHS

      The COSINE-MHS community is mainly formed by European X.400
      service providers from the academic and research area, each of
      which is a member of RARE.  The COSINE-MHS community is used in
      the annex as an example for the usage of this document in a
      multinational environment.

3. Requirements

   X.400 MTAs can communicate using different transport and network
   protocol stacks.  For this document the stacks used in a WAN
   environment need to be considered:

                           Stack 1    Stack 2    Stack 3    Stack 4

      Transport Layer 4    TP0        TP4        RFC 1006    TP0
      Networkservice 1-3   X.25       CLNS       TCP/IP     CONS

   A common protocol stack is not the only requirement to enable
   communication between two MTAs.  The networks to which the MTAs
   belong need to be interconnected.  Some well known networks are
   listed together with the stacks they use.

      Network                                Stack   Abbreviation

      Public Switched Packet Data Networks     1     Public-X.25
      International X.25 Infrastructure EMPB   1,4   EMPB-X.25
      US and European connectionless pilot     2     Int-CLNS
      Internet                                 2,3   Internet

   Note that several stacks may be supported over a single network.
   However communication between MTAs is only possible if the MTAs share
   at least a common stack AND a common network.

   Unlike SMTP/TCP/IP systems, there is no directory service available
   which would allow an MTA to look up the next MTA to which it should
   submit a message.  Routing within X.400 will continue to be table
   based until a solution using X.500 directory services is available.

   Furthermore it is not generally allowed to connect to any MTA even on
   the same network without being registered on the destination MTA.
   These restrictions require a large coordination effort and carefully
   configured and updated systems.



Eppenberger