ith a search key of 36 bits. Therefore, capacity and speed are the two most important rating parameters for the specification of a search engine's performance. Because the word size is 36 bits (and not 32 bits as in normal mem- ory) when using the convention of calling a search engine with 1Mb or 2Mb capacity, we obviously mean they contain 1.125Mb or 2.25Mb, respectively. One can cascade search engines and increase the capacity, although this may adversely affect the latency of the overall system, as more cycles may be needed from the moment that a key is presented to the search engine until the moment when a result has been produced at the output port of the engine. The reader is referred to Chapters 12 and 13 for more details. We also expand on other interesting topics associated with this subject in Chapter 15, "Traffic Managers." Packet Parsing Unlike the traditional ATM environment, where all cells are of equal length, deep packet inspection is not a trivial operation when incoming packets are of variable length. Special architectural capabil- ities must be designed in order to ensure a flexible handling of the field alignment for subsequent pro- cessing. Network processors are very well suited for this type of function. Some contain embedded 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 PACKET PROCESSING 55 functionality that can do this, whereas others must be augmented by ancillary chips (preferably from the same chipset family and vendor) to implement the desired scheme. Packet Classification and Fast Forwarding The two terms packet forwarding and packet routing may confuse some readers at this point. On one hand, forwarding refers to the selection of an output port by a switch/router based on the destination address of the packet and in conjunction with a routing table that stipulates what goes where. On the ot