Mạng và viễn thông P23

The Message Handling System (MHS)The message handling system(MHS) is a concept developed by ITU-T thatis intended to lead to the interconnectivity of all different types of message conveying systems, e.g. telephone, telex, facsimile, electronic mail, etc. MHS sets out a simple model of basic interconnection between systems. As it does so it defines a new dictionary of standard terms and jargon to describe the various phases of a communication.
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Mạng và viễn thông P23 Networks and Telecommunications: Design and Operation, Second Edition. Martin P. Clark Copyright © 1991, 1997 John Wiley & Sons Ltd ISBNs: 0-471-97346-7 (Hardback); 0-470-84158-3 (Electronic) 23 The Message Handling System (MHS) The message handling system(MHS) is a concept developed by ITU-T thatis intended to lead to the interconnectivity of all different types of message conveying systems, e.g. telephone, telex, facsimile, electronic mail, etc. MHS sets out a simple model of basic interconnection between systems. As it does so it defines a new dictionary of standard terms and jargon to describe the various phases of a communication. Inplaces it mayeven seem trivial, but the careful definition is worthwhile if it willsolve today’s incompatibilities. This chapter seeks to explainthemodel, unravel the jargon and describe the initiatives that will result.23.1 THENEED FOR MHS It is commonplace today for a wide variety of telecommunications technologies to be provided in the sameoffice. Often a number of technologies provide similar but separate means for conveying identical information, but many users still employ more than one of the methods. Telex, facsimile and electronic mail all provide means of transferring text or documents. One or other of the different devices may be favoured to convey information to a given destination, depending on the facilities available at the far end, for despite the commonality of each of the different methodsof document transfer, they are mutually incompatible and will not interwork. MHS defines a simple model of the procedureneededfordocumentstobepassedelectronicallyina store-and-retrieve fashion between a wide range of different types and makes of office business machines (e.g. word processor, facsimile machine, teletype, maybe even the telephone as well). In time, the modelwill lead on to thedevelopment of communication standards, interfaces and equipment needed so that machines of dissimilar types may intercommunicate.23.2 THE CONCEPT OF MHS The underlying assumption on which MHS is founded is that during any period of communication only the information content of a message is important. The corollary 413414 THE MESSAGE HANDLING SYSTEM (MHS) is thatthemeans of message conveyance is immaterial, andtheformat of the information (e.g. facsimile, telex, electronic mail, etc.) may be changed between the originating and destination stations. Thus the originator need not worry about whether a compatible facsimile or telex machine is available at the destination, because MHS will provide conversion to the required format. ITU-T’s recommendation X.400 defines a model of message handling ( M H ) service, a provided by means of a message handling system ( M H S ) . The M H service allows the conveyance of messages across a network on a store-and-forward or store-and-retrieve basis. Thus information between sender and recipient can be sent without interrupting the recipient from his current activities: themessage is dealt with when it is convenient. This is important in computing activities if the receiving machine is already busy. It is also important for human recipients who might be away from their desks. Much like a postal system, messages may be posted into the system at any time of day and will be delivered to the recipient’s mailbox. The recipient is free to sort through the incoming mail at any time of day, and as soon as an item is accepted by the designated recipient, automatic confirmation of receipt can be despatched back to the sender. This eliminates any possible concern about whether the recipient has seen a given item.23.3 THE MHS MODEL The MHS model provides a designaid to thedevelopmentofnetworksproviding message handling services. It based upon the principles of the International Organiza- is tion for Standardization (ISO) open systems interconnection ( O S I ) model (as described in Chapter 9). Like OSI, MHS is a layered model with g ...