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The X.400 specification was first published in 1984 as X.400/84 and was significantly expanded in 1988 as X.400/88 and in 1992. In the 1984 version, service characteristics of the presentationlayer are assigned to the application-oriented service, which is primarily classified in the applicationlayer. X.400 defines two services in this version: The Message Transfer Service (MTS) and the message service between persons, the Interpersonal Messaging System (IPMS).

The 1984 functional model defines a spatially distributed system whose services can be used by users by sending and receiving messages. The user agent is an application process that makes the services of the messaging system available to the user. A User Agent is a software that performs the functionalities such as generating, sending, receiving and archiving messages. Each UA is identified by an address.

Functional model for MHS according to X.400 (84)

Functional model for MHS according to X.400 (84)

The 84 version of X.400 recognizes three P protocols for communication between Message Transfer Agent Entity (MTAE) instances and User Agents (UAE). The P1 protocol is the MT layer protocol for switching and forwarding messages between MTAEs. The P3 protocol provides for the exchange of messages between Submission and Delivery Entity (SDE) and Message Transfer Agent Entity (MTAE), and the P2 protocol is used for UAL layer communication between User Agents (UAE) instances. Not defined is the Pt protocol, for the interface between user and user agent. This allows these interfaces to be developed on an application-specific basis.

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Englisch: X400/84
Updated at: 09.12.2016
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