OSI/MHS Orientation Guide

Building Your Message Handling System
OSI/MHS Orientation Guide—424829-001
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Integrating 1984 and 1988 Messaging Systems
Integrating 1984 and 1988 Messaging Systems
Although several companies have announced products conforming to 1988 X.400, the
great majority of existing systems implement the 1984 Recommendations. Even among
those able to exchange messages in 1988 format, the underlying services, such as the
reliable transfer service and the OSI stack, are of the earlier vintage. This likely mix of
systems in your messaging network gives rise to special planning and configuration
problems.
What You Need to Do
The 1988 version of X.400 differs from the earlier version in several major respects.
Following is a partial list of changes:
•
It supports a message store (MS) and a protocol for access to it (P7).
•
It supports named distribution lists, so message originators need not explicitly
specify all recipient names.
•
It expands the earlier definition of access units for integrating other types of devices
and delivery services (like telex or physical delivery systems) with X.400 networks.
•
It supports additional encoded information types by prescribing a means to identify
a nonstandard information type as externally defined.
•
It expands the options available for interpersonal messages and for message delivery
services in general.
•
It prescribes the use of a full OSI stack, and specifically the use of ACSE for
establishing associations. (The 1984 version of the reliable transfer service ran over
the Session Layer; the 1988 version also uses ACSE and the Presentation Layer.)
•
It defines several new types of reports.
•
It introduces limits on message size (2 megabytes in many implementations).
Fortunately, a 1988 implementation is able to interoperate with earlier implementations.
It does so by downgrading its own operation, stripping 1988 messages of elements
undefined for 1984 and emulating the operation of 1984 OSI services. Certain 1988
messages and reports cannot be sent to a 1984 system; in such cases, a 1988
implementation sends a nondelivery report to the 1984 MTA. Depending on the
implementation, a distribution list name can be passed to an 1984 MTA as just another
X.400 name. The 1984 MTA cannot expand the distribution list name, but it can route
the message to a location identified by that name.
Therefore, the major tasks and considerations for creating a multiversion network are
•
Describing the 1984 messaging system (or a system that carries 1988 messages over
1984 services) to OSI/MHS
•
Developing a routing strategy that minimizes the use of 1984 systems to relay
information between 1988 systems (because in such cases value is lost in transit
through the 1984 MTA)