d with rack-mounted devices and modem banks. A small footprint of these rack-mounted and chassis devices. Low power consumption as racks at carrier premises have tight constraints that must be respected. The ability to communicate in multiple physical interfaces and layer 2 protocols. 1. See, for instance, "The Role of Network Processors in Next Generation Networks: Defining the New Network Processor Landscape from CPE to Core," a white paper from Intel Corporation, Network Processor Division, August 2001. 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 50 NETWORK PROCESSORS For edge network equipment designers, the problem is not how to collect low-speed traffic from users or how to distribute it to them. It is how to aggregate multiple traffic streams (flows) into traf- fic classes that reflect specific characteristics of differentiated services. Therefore, the designer of edge equipment is interested in ensuring that Services can be easily provisioned when and where they are needed. Both the performance and functionality of the equipment are scalable. The density of the design must be maximized. The reliability and availability of the design must be optimized for this context. The network equipment can be serviced, maintained, and upgraded easily. The design is modular SO that it can be expanded and upgraded with new protocols, standards, and required functionality such as customized billing. The core network is comprised of optical fibers connecting hundreds, if not thousands, of edge routers and switches, each requiring the ability to handle hundreds of gigabits-per-second traffic and often having a terabits-per-second switching capacity. The designer of core equipment is preoccupied with the following characteristics: Scalable performance when switching or routing. High reliability. High availability. Fault tolerance 