Computer Networks: The Physical Layer

2.6 Broadband ISDN and ATM

Highlights

2.6.1 Virtual Circuits versus Circuit Switching

Virtual circuits are made by reserving bandwidth at all the necessary switches between the source and destination. Reservations are kept track of at the switch via tables which store the information needed to direct packets to the right place.

2.6.2 Transmission in ATM Networks

ATM is asynchronous because it does not guarantee that cells will be taken from each source in turn; instead, ATM transmits cells as they arrive, no matter what order. ATM is designed to be compatible with SONET, but it can run on the fiber and non-fiber media as well (only under special conditions).

2.6.3 ATM Switches

ATM switches are often synchronous (taking one cell from each input line in turn). The small size of the ATM cell was carefully thought-out: it is small enough to go through switches at very fast rates. There are numerous switching algorithms that have been developed for ATM, such as the Knockout Switch and the Batcher-banyan switch, and new ones are being designed all the time.

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