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Mạng và viễn thông P24

Mobile and Radio Data Networks Just as computers and datacommunication are revolutionizing office life, so mobile and radio data networks are enabling corporate computer networks be extendedto every part of the comto pany’s business, including the mobile sales force, the haulage fleet and the travelling executive. Data network techniques can now also be usedto trace and pinpoint trucks on the roador ships at sea. | 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 24 Mobile and Radio Data Networks Just as computers and datacommunication are revolutionizing office life so mobile and radio data networks are enabling corporate computer networks to be extended to every part of the company s business including the mobile sales force the haulage fleet and the travelling executive. Data network techniques can now also be used to trace and pinpoint trucks on the road or ships at sea. This chapter discusses some of the most recent radio data network technologies covering the principles of radiopaging mobile data networking wireless LANS as well as describing radiodetermination services. 24.1 RADIOPAGING Radiopaging was the first major type of network that enables transfer of short data messages to mobile recipients. Initially it was a method of alerting an individual in a remote or unknown location typically by bleeping him to the fact that someone wishes to converse with him by phone. Subsequently the possibility to send a short text message to the mobile recipient became commonplace. To be paged an individual needs to carry a special radio receiver called a radiopager. The unit is about the size of a cigarette box and is designed to be worn on a belt or clipped inside a pocket. The person carrying the pager may roam freely and can be paged provided they are within the radiopaging service area. The service may provide a full nationwide coverage. Figure 24.1 illustrates a typical radiopaging receiver. The initial radiopagers were allocated a normal telephone number as if they were standard telephones. Paging was achieved by dialling this number as if making a normal telephone call. Instead of being connected through to the radiopager the caller either speaks to a radiopaging service operator or hears a recorded message confirming that the radiopager has been