mphasized. Bandwidth is typically not a scarce resource in the enterprise, but it may be scarce with a service provider. The differences between performance expectation and quality of service (QoS) treatment require- ments must be considered. The operating environment requirements are very different in the two realms. For example, the requirements for a central office differ from those for a street cabinet/pole top where there is no forced air cooling and ambient temperatures can vary between great extremes. The two realms have different requirements in terms of reliability/availability and how easily the equipment can be upgraded in the field. The requirements for accommodating varying operations, administration, maintenance and provi- sioning requirements in both cases. In the current WAN realm, both fast IP switching techniques and Multiprotocol Label Switching (MPLS) must be supported. This means that wire-speed IP routing at OC-192 is required. As men- tioned previously, in addition to increased routing speed, MPLS offers carriers some unique capabil- ities for virtual private networks (VPNs) and other revenue-generating services based on its traffic-engineering (TE) advantages. Network processors are becoming useful for the timely design of advanced, but affordable, equipment that provides the manufacturer's clients with the possibility for such differentiation and potentially lucrative services. The WAN edge routers must be able to consolidate multiple access network interfaces. A typical example of this environment is a Cisco Edge Service Router that can provide the equivalent sustained throughput of 43 T3 lines. A modular design allows multiple combinations of throughput-for instance, in multiples of T1 or even fractional T1. The uplinks from the access network can be found in Gigabit Ethernet or more often in OC-12 links. These WAN edge routers must be extremely reli- able to ensure around-the-clock functionality. This implies that they must be designed to be field serv- iceable. In other words, critica