uld first look at the interesting variations on what a switch/router should be able to do in each situation. LAN traffic is now mostly a mixed landscape of switched 10 and 100 Mbps Ethernet, while legacy token rings are also used in some cases and more and more Gigabit Ethernet is showing up on the LANs inside the enterprise network level. Traffic is generally switched at layers 2 and 3. Workgroup switches are network units that consolidate all the disparate users generating this traffic demand. This is done in a cost-effective way. Web switches (load balancers) on top of traditional layer 3 switching must also be able to switch traffic at layer 4 (for example, at the Transmission Control Protocol [TCP] layer) all the way up layer 7 (for example, for cookie detectors). In this case, traffic would need to be switched according to each application and based on the Uniform Resource Locator (URL). LAN backbone switches aggregate all the enterprise workgroup switches and provide connectiv- ity to the access network. Gigabit Ethernet is used in this situation, as switching multiple protocols at layer 3 has replaced the need for the cumbersome and expensive routers that originally handled this type of traffic. Because each individual access line for routers at the edge of the access network has a speed of less than 10 Mbps, the switching requirements are well below the high-speed processing capabilities of the network-processing chip architectures that we discuss in this book. 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. PACKET PROCESSING PACKET PROCESSING 47 We should mention some overall contextual differences between enterprise and service provider equipment: At times, multiple end customers who are typically indifferent toward each other's needs must be served. In many cases, the importance of managing bandwidth intelligently cannot be overe