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ATM Concept


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  ATM Concept

In the ATM-based networks, all forms of user traffic are segmented into uniform data units of small size and routed through the switching nodes and transmission links of the network. The users would have bandwidth on demand, and the underlying network would be based upon a single switching and multiplexing principle. This capability has been viewed as especially important for multimedia services, where a given call may contain voice, data, and video information.

ATM opens the telecommunications information-transfer modes not only to circuit switching but also to packet switching and statistical multiplexing i.e. ATM supports all of these schemes. ATM is a virtual connection-oriented bearer technique based on the use of fixed size, small packets called cells (53-byte packets-5 byte cell header and 48-byte payload). Cells are switched across the ATM transport network. The cell header provides control information on a per-link basis, including two logical connection identifiers (VPI and VCI); the type of cell payload (OAM&P or user cells); and the HEC sequence. Prior to sending data, an ATM end-to-end connection should be set up either on

  • A permanent basis (by network-management intervention) or

  • A dial-up basis (by network signaling).

The connection-oriented nature of ATM provides for resource reservation capability transmission link by transmission link, from end user to end user, and throughout all the switching nodes on the connection path. Resource reservation is executed at connection set up, though the re-negotiation of the terms of an active connection contract is possible. If at any intermediate link of any available source-destination path the network is not able to offer the requested resources (for example, a given dedicated bandwidth to the end-to-end connection), the connection request is refused and the network access is blocked.

Like packet switching for data (e.g., X.25, frame relay, transmission control protocol [TCP]/Internet protocol [IP]), ATM integrates the multiplexing and switching functions, is well suited for bursty traffic (in contrast to circuit switching), and allows communications between devices that operate at different speeds. Unlike packet switching based on best effort IP traffic, ATM is designed for high-performance multimedia networking. ATM technology has been implemented in a very broad range of networking devices:

  • PC, workstation, and server network interface cards

  • switched-Ethernet and token-ring workgroup hubs

  • workgroup and campus ATM switches

  • ATM enterprise network switches

  • ATM multiplexers

  • ATM–edge switches

  • ATM–backbone switches





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Last modified: July 13, 2016


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