ding 1,000 Small number Usually WRED, two to and limited three priority levels classification Until recently and to a large extent still, networks have been treating transient traffic on a best- efforts basis. Unfortunately, this is not good anymore. In addition to e-mail and file transfers, remote login, or typical web browsing, numerous telephone conversations or videoconferencing may also be occurring, or multicast multimedia material may be downloaded on a pay-per-use basis for entertain- ment purposes. All these unrelated applications must share the common network, and it would be unfair to treat them all in the same way. In addition to fairness, the concept of profitability is important as service providers and carriers must manage their single most important resource-bandwidth (or throughput, which can be translated to used capacity and is a metric that will tell the carrier how much more rev- enue could be generated if traffic were managed in a different way). Bandwidth must be allocated dif- ferently among paying customers at different times of the day in order to maximize revenue and customer satisfaction. From this fundamental premise, the concepts of QoS and guaranteed-level serv- ice were born. The idea is not new. For more than 20 years now, type of service (TOS) bits have been available as part of the definition of the classic IP packet. The basic notion was already in place. This has only facilitated the wide-scale adoption of the QoS vision. However, as we will see, many issues still need to be agreed upon and implemented. 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. TRAFFIC MANAGERS 314 NETWORK PROCESSORS In any discussion on QoS, keep in mind that QoS seeks to specify and control five fundamental network variables: Bandwidth or throughput For example, a critical telemetry application may require a higher pri- ority for 