Protocols and Application Service Elements for X.400

Table of Contents

Protocols

P1 Protocol

The P1 protocol handles the layout of a message sent from one Message Transfer Agent (MTA) to another Message Transfer Agent. This Protocol is the equivalent of a letter and an envelope. The 'envelope' is known as the P1 header and the 'letter' is the P2 Message. Addresses of the recipient must be globally unique for the P1 Protocol So the address of the recipient is fully qualified (ie. looked up using X.500 Directory Service). (MGMT: check this link)

P2 Protocol

The P2 protocol is the way in which the sender and the recipient know in what format the message is being transmitted. This means that both sides should be able to understand the meaning of the messages being sent.

P3 Protocol

The P3 protocol is how the Message Transfer Agent (MTA) communicates with the User Agent (UA). The User Agent (UA) prepares a message and transmits it to the Message Transfer Agent (MTA) . This protocol also is used to deliver a message directly to the User Agent (UA) from the Message Transfer Agent (MTA) Because the User Agent is not always available there is a Message Store.

P7 Protocol

The P7 Protocol is for communication between the User Agent (UA) and the Message Store (MS). P7 provides facilities to select messages selectively from the Message Store (MS)

Application Service Elements (ASE)

Application Service Elements (ASEs) are abstractions of a group of functions used by Application Entities (AEs eg. Message Transfer Agents, User Agents) to interact with each other. Their purpose is to help describe how they provide services using the lower levels of the OSI model.

In X.400 the following ASEs are used

  • The Message Transfer Service Element (MTSE) allows Message Transfer Agents to communicate reliably. This is associated with the P1 Protocol.

  • The Message Submission Service Element (MSSE) allows a User Agent to submit a message to an entity it is connected with (eg. MTA, MS). This is associated with the P3 protocol and the P7 protocol.

  • The Message Delivery Service Agent (MDSE) allows a MTA to deliver a message to the UA. This is associated with the P3 protocol.

  • The Message Retrieval Service Element (MRSE) is the way a UA gets a message from the Message Store (MS). This is associated with the P7 Protocol.

  • The Message Administration Service Element (MASE) helps the UA to take care of administrative functions.

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    This Page created by: Kevin Bushe, kbushe@alf2.tcd.ie.