eatures not only provide a series of unique benefits, but they are also justified in an extremely competitive industry. Network processors promise to combine high performance with versatile functionality while providing ease of use, flex- ibility, and rapid development. They are a predominant enabling factor for this new phenomenon. In this book, we have been looking under the hood of these devices. High-speed communications and network-processing equipment contain some clearly defined units of functionality. Once these are combined into the appropriate modules and system configura- tions by the manufacturer's engineering departments, they enable the creation of the broadband or high-speed switching/routing network gear. In this chapter, we will look at some of the most successful and representative techniques for implementing the switching function. We will distinguish the underlying common denominators of the various technology modules and examine many trade-offs. We will then look at other functions required inside fast network switching/routing equipment. The next two chapters should hopefully provide a clear understanding of and better appreciation for the complexity and architectural trade- offs involved in the design and implementation of advanced switch fabrics and traffic managers-two of the most critical processing units with which network processors must be able to interface in order to carry out their complex mission in life. So far, we have seen the architecture and internal structure of many different network processors. Hopefully, by discussing the internals of switch fabrics (and traffic managers in the following chap- ter), we can better appreciate the challenges of systems design, follow the internal technical descrip- tion and/or justification of new or existing switch fabric products, better appreciate the differences in architectural decisions that the various vendor design teams have made as well as the reasons why the respective decisions were made either at the systems or component level, 