ATM Last modified: Wednesday, February 26, 2003
Short for Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line. Some people think that ATM holds the answer to the Internet bandwidth problem, but others are skeptical. ATM creates a fixed channel, or route, between two points whenever data transfer begins. This differs from TCP/IP, in which messages are divided into packets and each packet can take a different route from source to destination. This difference makes it easier to track and bill data usage across an ATM network, but it makes it less adaptable to sudden surges in network traffic. When purchasing ATM service, you generally have a choice of four different types of service: constant bit rate (CBR): specifies a fixed bit rate so that data is sent in a steady stream. This is analogous to a leased line. variable bit rate (VBR): provides a specified throughput capacity but data is not sent evenly. This is a popular choice for voice and videoconferencing data. available bit rate (ABR): provides a guaranteed minimum capacity but allows data to be bursted at higher capacities when the network is free. unspecified bit rate (UBR): does not guarantee any throughput levels. This is used for applications, such as file transfer, that can tolerate delays.
Asynchronous Transfer Mode tutorial  This tutorial presents an overview of ATM and Gigabit networks and provides links to sections on network descriptions, benefits, switching techniques, definitions, and services. The ATM Forum  The ATM Forum site is dedicated to promoting ATM within various markets. There are links to general information about the forum and its members, along with ATM technical and marketing information. ATM dictionary Contains definitions for terms associated with ATM. ATM internetworking paper from Cisco Systems A table of contents page with links to download the entire paper in either Adobe Acrobat or Postscript. ATM Tutorials and Resources Good collection of links to ATM information, including tutorials, papers, FAQs, and forums. This page is hosted by the InterOperability Lab at the University of New Hampshire. Cell relay FAQ Provides information on cell relay and ATM technologies. The ATM Consortium The ATM Consortium home page offers links to general and membership information, technical information including test suites and equipment lists, and educational information. The Cell Relay Retreat Provides a collection of ATM resource information. Included are links to tutorials, documents, trade press resources, archives, and FAQs.

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