ATM (Asynchronous Transfer Mode) | LAN Technologies | Pearson IT Certification

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ATM (Asynchronous Transfer Mode)

Asynchronous Transfer Mode (ATM) is an adaptable technology that can be used
in LANs and WANs (Wide-Area Networks). ATM is based on the efforts of the ITU-T
Broadcast Integrated Services Digital Network (BISDN) standard.

ATM uses both switching and multiplexing, and it can provide very high
bandwidth with few delays. Instead of using frames like Ethernet uses, ATM uses
53-byte, fixed-size cells. The first five bytes contain cell-header information,
and the remaining 48 bytes contain the payload (user information). It was
originally conceived as a high-speed transfer technology for voice, video, and
data over public networks. Small fixed-length cells are best suited for
transferring voice and video traffic because they are intolerant of delays that
result from having to wait for a large data packet to download (among other
network activities). Although ATM is not dependent on a Physical-layer
implementation, it does require a medium such as fiber optic to support the
amount of bandwidth that’s needed to run ATM.

ATM’s chief advantage is its capability to create a seamless and fast
network reaching from the desktop out across a wide area. Ultimately, ATM could
do away with routers, allocate bandwidth, and be able to run high-end
applications. Although ATM’s potential certainly sounds like a dream for
networks, the technology also has disadvantages. ATM uses a great deal of
overhead and carries many additional expenses. Because most organizations are
only pushing data through their network with a few higher-end applications, the
need for millisecond synchronization is not a necessity. ATM has a large
overhead, and most companies—those with networks that usually push data and
very little video—may not even notice the difference, making the overhead
and expense of ATM an unwise investment.

ATM appeals mainly to companies that need to deliver synchronized video and
sound. The companies that benefit from ATM are movie and entertainment players,
such as Time-Warner, that want to deliver on-demand video and sound to your
home. At this point, ATM is overkill for most companies passing data, but it has
continued to gain popularity over the years and may continue to do so in the
future. Some phone companies have adapted the technology and use it over Digital
Subscriber Line (DSL) with a technology called ATM over DSL.