 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 328 NETWORK PROCESSORS (RCS), and Generalized Processor Sharing (GPS). An exhaustive listing or description of these algo- rithms is beyond the scope of our coverage. For more information, refer to literature on this topic. As an example of real-life applicability, we will mention that although the DiffServ EF PHB does not define the queuing algorithm, typical implementations are based on some combination of PQ and WFQ. In the AF PHB, although RED is used as an example in the IETF's RFC draft, WRED is pre- ferred in practical systems. It is implemented in some combination with CBQ and WFQ scheduling. In real-life designs, some system-design choices may require compensation through the engage- ment of complementary techniques. For example, some systems implement PQ (SP scheduling), but to avoid completely penalizing lower-priority traffic, they must do it in conjunction with some elab- orate traffic policing that simultaneously controls the rate of the high-priority traffic coming in. These numerous blends of complementary functionality and an algorithmic approach are usually character- istics of product offerings through which network processing chip vendors or NEVs try to systemat- ically differentiate their products. We will now turn our attention to buffer management. The ultimate goal is to apply differentiated treatment on packets as a scalable means of offering sophisticated and scalable QoS. As shown in Figure 15.4, classified, policed, and shaped traffic is buffered (and therefore delayed in a controlled manner) before it gets scheduled. The appropriate buffering levels are usually decided from the corresponding SLA. Buffer management is a wide set of problems and techniques proposed as solu- tions. More specifically, in buffer management, a designer should be concerne