 which consolidated discussions and guided the industry into several new stan- dards. These standards are referred to generically as MPLS. These layer 3 switching techniques enable the introduction of many new interesting services. Virtual LANs (VLANs) and full-fledged virtual private networks (VPNs) became feasible. Traffic engineering (TE), QoS, and the level of priorities are some of the issues that network equipment man- ufacturers can address while tailoring their offerings to their customers at easily justifiable costs. MPLS, LAMBDA SWITCHING, AND WAVELENGTH ROUTERS Traditional mesh-connected routing networks require any-to-any connectivity between all routers. This leads to the need for nX(n-1)/2 virtual connections, for example, on an ATM network with n nodes. This obviously means that if a new router must be added, a virtual connection will be man- dated with all the other routers. That is a problem. Beyond this shortcoming, a network failure or topology change will provoke a massive amount of traffic that was generated by a routing protocol. Each router will have to communicate routing updates across each virtual connection to which it is connected in order to inform its neighbors about the new IP network reachability situation. As if these problems were not enough, let us, for a moment, think about the following situation. A typical ISP network contains multiple routers at the edge of the ISP's network that have peer rela- tionships with other ISP routers with which they exchange routing table information to provide global IP connectivity. In order to find the optimal path to any destination outside an ISP's network, the routers at the core of the ISP network must be made aware of all the network reachability informa- tion. Routers at the edge of the network can acquire this knowledge from the adjacent routers (which are outside the ISP network) that they are peering with. The result of this uncomfortable situation is 55. Radia Perlman, Interconnections: Bridges, Routers, Switches, and Internetworking 