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ATM

ATM stands for Asynchronous Transfer Mode. ATM is a cell switching technology. It is a high speed capacity technology and uses 53 bytes cells containing a 48 bytes payload. 

ATM 53 Bytes Cell

It was initially designed as the data-link protocol of B-ISDN. The data transfer rate is scalable from 25-622 Mbps. The important standard is that for 155Mbps.
This is a switching technology unlike shared traditional LANs. The same technology can be used in wide area networks as well as in the local area. And because of its fixed length cells, it allows fast switching by hardware as opposed to switching done under program control which is slower.

The three main implementation areas are:

1. LAN desktop.
2. LAN Backbone.
3. In the wide Area.

The main strengths are that it supports multimedia, voice and video as well as data. It provides defined Quality of Service QoS. Its scaleable supporting a wide range of  speeds. It is becoming important in WANs because of extensive Telco support.

Its weaknesses are that it has numerous competing and often overlapping standards. Traditional technologies cannot often implement the QoS provision in ATM and downgrade network.

ATM interfaces as Bridge

The interface emulates a bridge. The incoming frames are fragmented by the interface into 48 byte pieces. The ATM cells traverse the ATM network carrying their 48 byte  payload until they arrive at the point of exit , another interface emulating a bridge. The exit interface reassembles the cells into a frame.

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Last modified: October 03, 2004