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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.

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