The Frame Relay protocol has its origin from the X.25 protocol. In order to make it suitable for fast data traffic a significant amount of overhead associated with the X.25 protocol was eliminated. For example,
node-by-node error checking and flow control was delegated to end-to-end error checking and flow control instead.
At the present time, the majority of Internet traffic is being carried over Frame Relay networks. However, as the ATM technology becomes more affordable, it is expected that the Internet traffic will
shift to ATM networks. The key factor for the switch from Frame Relay to ATM is due to limitation of scalability for higher bandwidths associated with Frame Relay technology.
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Copyr ight © CRC Pr ess LLC
by Abhijit S. Pandya; Ercan Sen CRC Press, CRC Press LLC
ISBN: 0849331390 Pub Date: 110198
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Chapter 5 ATM Protocols
Protocols for computer communications are defined as sets of rules and message exchanges between computer systems. In order to talk to another computer, it is essential to understand its communication
protocol. Typically, various communication functions involved in networking are divided into specific tasks and spread among the layers. The most well-known protocol architecture is the seven-layer Open
Systems Interconnection OSI model.
A protocol stack is a set of layers that incorporates standards of one system or another at each layer. There are many different kinds of protocol stacks. The connector on the back of a computer or the
communications board is referred to as the lowest layer while the applications program running in the local memory of the computer or the network device is referred to as the highest layer. The protocol
stack bridges the gap between the hardware i.e., the connector and the software i.e., the applications program.
As shown in Figure 5-1 a protocol stack includes a variety of components necessary for providing a complete solution for the user’s networking problems. Signaling protocols are necessary for controlling
the network. Other components include a method for monitoring the network performance and a means for managing both, the resources and the traffic on the network. It also includes a protocol for
internetworking with older networking technologies.
The protocol stack can often be proprietary, i.e., wholly developed and owned by a private company, and the company is under no obligation to reveal the internal functional details to anyone. IBM’s System
Network Architecture SNA is an example of a proprietary protocol. There are other protocols that are available to everyone and referred to as an open standard. ISO and the popular Transmission Control
ProtocolInternetwork Protocol TCPIP belong to this category where documentation is available from a variety of sources.
I. ATM Protocol Stack
ATM is an open standard based on the documentation available from the ITU-T and the ATM forum. It
