Avaya M-ACCF/SF manual ATM is Service Transparent, Service Processing

Chapter 1 Overview

physical layer technology to share the same higher layer — the ATM layer.

ATM uses fixed length packets called cells. The ATM cell is defined as 48 bytes of payload and 5 bytes of header information totaling 53 bytes. The header contains enough information to allow the network to forward each cell to its proper destination. The cell header also provides the network with the ability to implement congestion control and traffic management mechanisms.

ATM advantages include the fact that:

•Fixed-length cells offer smaller and more predictable switching delays, because cell switching is less complex than variable-length packet switching.

•Having all the data in the same cell format also dramatically increases the speed of transmission, by eliminating the need for protocol recognition and decoding. A good analogy is containerized shipping, where uniform shape and weight containers with standardized labelling, ease and speed up processing.

•Cell switching is less complex and more reliable. ATM hardware can be implemented more efficiently because control structures, buffers, and buffer management schemes can be designed to known size criteria.

•Cell-relay switches can process cells in parallel, achieving speeds that far exceed the limitations of packet switch architectures.

•The cell format also allows for multi-protocol transmissions. Since ATM is protocol transparent, the various protocols can be transferred at the same time. With ATM, one line can carry phone, fax, video, data and other information simultaneously. This multiprotocol advantage also offers scalability, greatly reducing the configuration changes necessary for adding a new traffic type to your network.

ATM is Service Transparent

ATM allows for the high speed transfer of a wide range of user traffic, including voice, video and other data.

The cell format means that more than one service (traffic type) can be multiplexed over the same physical line, see Figure 1.9.

Figure 1.9 Service Processing

Avaya M770 M-ACCF/SF ATM Access Modules User’s Guide 17