ppropriate level of attention or with the necessary sense of urgency at an ingress port, input buffers may overflow due to traffic congestion. This could lead to packet loss. If the same traffic congestion occurs at an egress port, then until the state of congestion is resolved, the latency and jitter figures may suffer unduly. This is somewhat similar to the revolution that Multiprotocol Label Switching (MPLS) has brought onto some IP networks. To form this revolution, MPLS borrowed the basic tagging idea from ATM 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 NETWORK PROCESSORS with its available bit rate (ABR), constant bit rate (CBR), and variable bit rate (VBR) classes of cells. In this case, special labels are tagged onto packets. Based on that marking, the network knows exactly how to treat these packets. The whole field of traffic engineering has almost acquired a new meaning following this revolution. As a result, new lucrative services such as the virtual private network (VPN) have become possible. Series of techniques and algorithms have been proposed, analyzed, documented, and implemented in order to materialize various methods that help create the framework of such traffic manipulation. Among them, we will mention methods of queuing, which allow the dynamic change in priority that some packets expect, as well as methods of deciding when, how, and which packets must be dropped (discarded). The traffic manager chips handle this through a scheduler module. Like other traffic man- ager modules, the scheduler module has its own memory subsystem where it keeps queues. The following are a couple of other functional modules inside traffic manager chips: The active queue control module, which uses its own memory subsystem where it keeps the so- called Random Early Detection (RED) tables. A statistics module, which often w