tailieunhanh - Mạng và viễn thông P22

Electronic Mail, Znternet and Electronic Message Services The ability to connect two computers together and, with relative ease, to send information from one to the other, is bringing a revolution in the way in which business and life as a whole is conducted. Today it is possible to run your bank account from home, book your holiday, send electronic messages to your work colleagues or friends, and look up to see what is on at the theatre in London orNew York companies may make their orders to and pay their bills from their suppliersby computer program and‘electronic data interchange’ | 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 22 Electronic Mail Internet and Electronic Message Services The ability to connect two computers together and with relative ease to send information from one to the other is bringing a revolution in the way in which business and life as a whole is conducted. Today it is possible to run your bank account from home book your holiday send electronic messages to your work colleagues or friends and look up to see what is on at the theatre in London or New York City. Alternatively companies may make their orders to and pay their bills from their suppliers by computer program and electronic data interchange . A number of technologies have enabled this revolution videotext electronic mail electronic data interchange EDI and Internet. We review the telecommunication aspects of these technologies in this chapter. VIDEOTEXT Videotext was the first type of device specially designed to allow telephone network customers to use a cheap device to access information from a large public database. The original technology and standards including special terminals and modem techniques allowing asymmetric transmission a high bitrate channel for information download to the customer with a low speed control channel for his ordering of different pages of information have now been overtaken by modern personal computer based technology but the appearance of the worldwide Internet has stimulated recent rapid growth for the long established videotext service providers British Telecom s Prestel Deutsche Telekom s Bildschirmtext BtX or Datex-J and France Telecom s Minitel . The idea of videotext is that using a low cost terminal in the form of a small television a customer can make a phonecall to a public central database where he could access all sorts of pages of information which he could then have displayed on