and better gauge the influ- ence at the systems level of component capabilities or characteristics. 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. SWITCH FABRICS 264 NETWORK PROCESSORS Hopefully, through this approach, the reader will not only acquire the basic knowledge of what the state-of-the-art technology is in this field, but he or she will also be able to independently perform a critical analysis and an objective evaluation of a platform or architecture comprising network process- ing, switch fabric, and traffic management and its suitability for a certain application and/or project. THE DEFINITION OF SWITCH FABRIC A switch fabric is a chip or a chipset that connects one or more among multiple inputs to one or more among multiple outputs based on some fundamental switching techniques and principles. For exam- ple, in a chassis-based switch/router, the switch fabric function is implemented on the switch fabric card or switch card, which is connected through the backplane to the multiple line cards. Switch cards serve as inputs and outputs to the rest of the network. Network processors and traffic managers usu- ally are situated on the line cards. High-speed connection techniques such as serialization/deserial- ization (serdes) components are needed on both sides of a link over the backplane to ensure the efficient and fast connection between the line cards and switch fabric cards. THE BASICS OF SWITCHING Before we discuss the switch fabrics themselves, we must discuss some fundamental concepts and notions about switching. These will be introduced as system concepts. The actual implementation of switch fabrics is of secondary importance for our purposes as the switch fabric user needs to know its macroscopic behavior in a system that he or she designs, but not necessarily the transistor-level con- nectivity of such an extremely complex