One of the major innovations in ATM is the use of 53-byte fixed-length cells, unlike conventional TCP/IP which uses variable-sized packets. This allows ATM users to build very fast circuits, simply because it is easier to process known data packet sizes rather than to have circuits trying to pinpoint the start and end of data packets. The small ATM packet (composed of a five-byte header and a 48-byte data 'container') also guarantees that voice and video can be slotted into the data stream frequently enough for real-time transmission.
Constant Bit Rate, which guarantees sufficient bandwidth for voice and video transmissions in real time, Unspecified Bit Rate, providing 'best effort' service for non-critical data such as file transfers, Available Bit Rate (ABR) which fine-tunes bandwidth according to LAN traffic congestion levels and Realtime variableBit Rate (rt-VBR) can support multimedia applications that require minimal delays
Another innovation in ATM technology is its ability to interconnect LAN and WAN protocols, allowing for a seamless transfer between WAN and LAN. One mode is called MPOA (Multi Protocol Over ATM) can be used to route TCP/IP protocols and IPX while maintaining ATM's quality of service.
LANE (LAN Emulation) modes allows it to interconnect between rival Ethernet and Token Ring, summarizing their frames or data packets in LANE packets and then converting these into ATM 53-byte cells. MPOA or traditional servers can be used to interconnect differing LAN segments, with the ATM communications protocols handling data transfers.
Posted by: Wasim Javed
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