OSI/MHS Gateway Programmatic Interface (GPI) Programming Guide

OSI/MHS Gateway Programmatic Interface (GPI) Programming Guide—424822-001
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Review of X.400 and OSI/MHS
This appendix is a brief summary of key X.400 and OSI/MHS concepts. It provides a
quick orientation to the X.400 gateway environment for readers who are new to
networking.
The topics covered are:
•
X.400
•
X.400 messages
•
Compaq OSI/MHS
•
X.400 gateways
X.400
X.400 is the official messaging protocol for the European community and for
Government OSI Profile (GOSIP) networks in the United States. X.400 defines a
functional model for a message handling system (MHS). Figure C-1 shows a general
view of the MHS model. The MHS model can be used to represent a single X.400
network; it can also be used to represent the global X.400 community.
An MHS user can be either a person or a computer process. A user that sends a message
is called an originator. A user that receives a message is called a recipient.
Messages are routed through the message transfer system (MTS). The MTS contains
message transfer agents (MTAs). MTAs can be compared to post offices. MTAs work
together to transfer messages and deliver them to intended recipients.
Figure C-1. X.400 Message Handling System
901CDT .CDD
Message Handling System
Message Transfer System
User User
MTA MTA MTA