rame relay and ATM, is called packet discard, shown in Figure 2-33. In the event that traffic gets too heavy based on preestablished management parameters, the switches simply discard excess packets. They can do this because of two facts: First, networks are highly capable and the switches rarely have to resort to these measures; second, the devices on the ends of the network are intelligent and will detect the loss of information and take whatever steps are required to have the discarded data resent. As drastic as this technique seems, it is not all that catastrophic. Modern networks are heavily dependent on optical fiber and highly capable digital switches; as a result, packet dis- card, while serious, does not pose a major problem for the network. Even when it is required, recovery techniques are fast and accurate. Because congestion occurs primarily as the result of inadequate buffer capacity, one solution is to preallocate buffers to high-priority traffic. Another is to create multiple queues with varying priority levels. If a voice or video packet arrives that requires high-priority, low-delay Figure 2-33 "Uh-oh too much traffic. Guess I'll have to..." " Congestion control with packet discard Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Protocols Chapter 2 treatment, it will be deposited into the highest priority queue for instan- taneous transmission. This technique holds great promise for the evolv- ing all-services Internet, because its greatest failing is its inability to deliver multiple, dependable, sustainable grades of service quality. Other techniques are available that are somewhat more complex than packet discard but do not result in loss of data. For example, some devices, when informed of congestion within the network, will delay transmission to give the network switches time to process their overload before receiving m