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C
AT M AND VLAN MANAGEMENT
BASICS
An Introduction to
ATM and VLAN
Management Basics
In 1986, the International Telecommunications Union (ITU) formed a
study group to explore the concept of a high-speed, integrated network
that could uniformly handle voice, data, and a variety of other services.
This resulted in BISDN, or the Broadband Integrated Services Digital
Network. BISDN services require high-speed channels for transmitting
digitized voice, data, video, and multimedia traffic. Asynchronous
Transfer Mode (ATM) is the switching and multiplexing technology for
supporting BISDN services.
One of the greatest challenges in defining ATM was to determine a
structure that could efficiently handle any type of traffic. Such a structure
must accommodate a variety of bit rates and support bursty
communications, since voice, data, and video traffic all exhibit bursty
behavior.
Packet-switching has been the technology of choice for bursty data traffic
because it consumes bandwidth only when traffic is present. Traditional
packet-switching mechanisms cannot achieve the performance and
speed required for real-time, two-way traffic. ATM overcomes this
limitation by offering fixed-length packets. Each ATM packet, called a cell,
consists of a 48-byte payload and a 5-byte header. Fixed-length ATM cells
offer several advantages:
■ Networking and switching queuing delays are more predictable with
fixed-length data cells.
■ It is less complex and more reliable to process ATM cells than
variable-length packets.
■ Fixed-length cells allow cell-relay switches to process cells in parallel,
for speeds that far exceed the limitations of bus-based switched
architectures