e are available. First, policies should be compiled about specific applications that are expected to run on a network that tries to implement QoS. Based on the collection of such disparate applications, the specific vari- ables that QoS seeks to specify and control are mapped onto each application. For example, jitter and latency requirements for voice over IP (VoIP) telephony are not the same as File Transfer Protocol (FTP) file transfers, and e-mail is not as high a priority as network management queries based on the Simple Network Management Protocol (SNMP) from the management console. Likewise, a long-distance carrier may have purchased a certain bandwidth of traffic on a backbone provider's network. This approach means that all traffic originating from the carrier must be moni- tored SO that a certain level of bandwidth can be guaranteed by the backbone. This implies the need for continuous monitoring on behalf of the network of the quality it delivers. In the previous exam- ple, if the intended performance drops below the preagreed levels, then bandwidth provisioning has to be revisited and perhaps modified on-the-fly. In addition to the vast amount of pertinent statistics of which modern network equipment keeps track, robust QoS-oriented metering processes and techniques need to be implemented. Metering helps detect specific situations and counts the instances and frequency of their occurrence. This way network management can monitor in real time whether they fit the intended profile of traffic. If they do not fit the profile, then special algorithms are used that will handle the shaping of traffic SO it con- forms to the desired profile. A special shaper module inside the traffic manager chips is responsible for doing this. It usually has its own external or internal memory subsystem within which it keeps and works with rate tables. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subje