OSI/MHS Orientation Guide

Building Your Message Handling System
OSI/MHS Orientation Guide—424829-001
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X.400 Message Handling Systems
•
Directory lookup requirements.
Most messaging systems cannot easily support applications with the following
requirements (although some are evolving to support the first two):
•
Very large messages (such as large, uncompressed computer files or imaging data)
•
Real-time delivery or guaranteed delivery of all messages within a very short time
interval
•
Remote file access in the context of online transaction processing
Of course, the same network can support both messaging applications and other types of
applications, such as bulk file transfer and directory services. For example, an OSI
network based on Compaq NonStop systems can provide messaging services through
OSI/MHS , and heterogeneous file transfer and access through the Compaq File
Transfer, Access, and Management (FTAM) implementation (Compaq OSI/FTAM).
Also note that flexible network connectivity is a key characteristic for messaging
systems. For example, OSI/MHS runs over Transmission Control Protocol/Internet
Protocol (TCP/IP) as well as over OSI transport protocols. (TCP/IP connectivity is
provided by the RFC-1006 enhancement of the Compaq OSI/TS product.)
X.400 Message Handling Systems
X.400 is the collective name of a series of CCITT Recommendations equivalent to the
OSI standard for message handling systems (MHS). Its goal is to define a message
handling infrastructure that can carry messages to and from users of different messaging
systems, across a heterogeneous network, as shown in Figure 1-1. There are two
versions of X.400: one was defined in 1984 and the other in 1988. A 1988
implementation can interoperate with a 1984 implementation.
Note. In this manual, the term “NonStop system” refers to a computer running the Compaq
NonStop Kernel. The term “Integrity Series system” refers to a computer running the NonStop-
UX operating system.
Note. To avoid confusion between references to the message handling standards and
references to the Compaq OSI products that implement the standards, this manual always
uses the term “X.400” to refer to the former and OSI/MHS to refer to the latter.