etail in Chapter 8.) If we can make a network behave in a connection-oriented fashion, we can allocate resources end to end that promise to meet the required service level. (In the LAN domain, today's 1Gbps and 10Gbps Ethernet standards provide a great deal of bandwidth, SO QoS is less of an issue. But when you get to the WAN edge, QoS becomes a greater concern.) The second objective of IP switching is to provide a way to scale economically because we know that data traffic is growing at a substantial rate (about 30% to 40% per year). IP switching basically replaces a network that consists entirely of Layer 3 hop-by-hop routing and the subsequent associated delays with a route-once/ switch-everything-else scenario. That is, the first packet between any two nodes is routed, and then all the subsequent packets between the nodes are switched at Layer 2 to the destination over the selected virtual circuit. This is referred to as a cut-through technique. IP switches vastly improve the performance at LAN/WAN LAN Interconnection and Internetworking IP Switch Video Room Private Systems Token Ring IP/ATM Switch Backbone Access Frame Ethernet Relay Switch Figure 6.14 A switched LAN infrastructure with an IP/ATM backbone integration points. As more routing lookup functions are moved from software into the ASIC chips, Layer 3 switches can inspect each packet just like a router at high speed, without using proprietary cut-through methods. Figure 6.14 shows a switched LAN infrastructure that makes use of a high- speed packet backbone, which could be IP, ATM, or MPLS. An Ethernet switch serves a cluster, and a token-ring switch serves another cluster. An IP switch serves a high-demand cluster. The infrastructure also includes individual servers as well as WAN access devices, all connected to the WAN edge devices, which in this case are the IP switches that help connect or establish a connection-oriented link end to end and thereby guarantee latencies and improve the performance associated with the internetwork. LANs and WANs Th