System information

CHAPTER
Troubleshooting ATM Switching Environments 21-431
21
Troubleshooting ATM Switching
Environments
This chapter describes the Asynchronous Transfer Mode (ATM) technology on which the
LightStream 2020 multiservice ATM switch (LS2020 switch) is based. ATM is a communications
standard based on cell relay techniques. The next sections discuss cell relay and ATM technology.
They also contrast ATM techniques with time-division multiplexing (TDM) and other
packet-handling technologies.
Cell Relay Packet Handling
Cell relay is a flexible and responsive method for multiplexing all forms of digital traffic (data, voice,
image, and video). Cell relay can handle rapid changes in the quantity and pattern of the traffic in
the network. All traffic is placed in fixed-length packets of information (cells) and switched at high
speeds. Cell relay is generally acknowledged as the best multiplexing technology for modern
communication applications because it combines the strengths of TDM and conventional packet
switching. Using cell relay packet-handling techniques, a mixture of bursty and delay-sensitive
traffic can be processed simultaneously, while at the same time providing the services required by
each traffic type.
Also, because cell relay processing is based on the use of small packets, the process technology is
adaptable and cost-effective for a wide range of interface speeds.
Technologies Compared
ATM technology first appeared in the Broadband Integrated Services Digital Network (BISDN).
However, ATM is now recognized as a useful technology in and of itself and is based on the
specifications and standards being developed by ITU-T (International Telecommunications Union
Telecommunication Standardization Sector), ANSI (American National Standards Institute), and the
ATM Forum.
Note ITU-T carries out the functions of the former Consultative Committee for International
Telegraph and Telephone (CCITT).
Each ATM cell contains a header and the data to be transferred. Cells are switched in the network
based on routing information contained in the cell headers. ATM transports all types of traffic (data,
voice, image, and video) using the same cell format.