X.400 Overview

The X.400 protocol is not a single protocol but a collection of X.4nn protocols intended to handle documents of any type from simple mail messages right up to full scale EDI data transfers.

This protocol wraps the data to be transferred in an electronic “envelope” that has a function similar to the paper envelope used in the postal system. The envelope keeps the information together, keeps it safe from loss or corruption, and holds the address of the final destination to which the contents must be conveyed.

The X.400 protocol has two basic areas of definition, the message handling system and the message transfer system. The message handling system defines the way that messages are presented to the “user”, known as the UA or User Agent. The message transfer system defines the protocol used to transfer messages across the communications link between two Message Transfer Agents or MTAs.

There are two main approaches to EDI using X.400. The P1/P2 approach is the simpler where P1 is the name for the envelope and P2 is the Inter-Personal Message or content of the EDI file. The more complex X.435 (sometimes called PEDI) approach uses the X.400 concept of EDIMs (EDI Messages) and EDINs (EDI Notifications) to control the flow of information.