The past few decades have seen the merging of computer and communication technologies. Wide-area and local-area computer networks have been deployed to interconnect computers distributed throughout the world. This has led to a proliferation of many useful data communication services, such as electronic mail, remote file transfer, remote login, and web pages. Most of these services do not have very stringent “real-time” requirements in the sense that there is no urgency for the data to reach the receiver within a very short time, say, below 1s. At the other spectrum, the telephone network has been with us for a long time, and the information carried by the network has been primarily real-time telephone conversations. It is important for voice to reach the listener almost immediately for an intelligible and coherent conversation to take place.

With the emergence of multimedia services, real-time traffic will include not just voice, but also video, image, and computer data files. This has given rise to the vision of an integrated broadband network that is capable of carrying all kinds of information, real-time or non-real-time.

Many wide-area computer networks are implemented on top of telephone networks: transmission lines are leased from the telephone companies, and each of these lines interconnects two routers that perform data switching. Home computers are also linked to a gateway via telephone lines using modems. The gateway is in turn connected via ...

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