ific traffic profiles that are simply desirable or that must be guaranteed by the network (in the case of SLAs). Based on multiple criteria, the network equipment may have to drop some packets. This is one of the tasks the traffic manager is called to handle. For example, the attainment of specific thresholds in some packet/flow queues may trigger the execution of congestion avoidance routines. Also as mentioned earlier, if the policing module of the traffic man- ager marks a packet with the appropriate color for demotion, then these packets stand a good chance of being discarded given the appropriate conditions. 2. An interesting work on this subject is the paper by A. Romanow and S. Floyd, "Dynamics of TCP traffic over ATM Networks," IEEE Journal on Selected Areas in Communications (May 1995). This is available on the Internet at ftp://ftp.ee.lbl.gov/papers/tcp_atm.ps. 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 326 NETWORK PROCESSORS SCHEDULING AND BUFFER MANAGEMENT In several examples presented already in the book as well as in the four-level framework of hierar- chical traffic management, as discussed earlier in this chapter, designers must manage queues that are logically distinguishable and onto which usually flows are mapped. These streams of packets, cells, or frames are stored (buffered) into some sort of memory and piled up in queuing structures that are tapped in a systematic manner. This implies that these buffers must be properly managed in order to ensure that the traffic shaping matches the overall context that we have described SO far. For example, consider a multiservice router (MSR) operating at an edge network that happens to be connected upstream with an OC-192 link and downstream (through four different line cards) to four OC-48 cards. Assume that each card contains 16 ports of Fast Ethernet (100 Mb