sandths of 20,000,000 or 30,000,000 will be affected because table entries in the search engine of this simple example must be reshuffled. This is an increase from 74,400 packets per second to a staggering 111,600 packets per second. Therefore, at least 74,400 packets per second will not be classified properly. The router, which must struggle to sustain wire speed, will probably just discard them. This is a huge number of packets to lose! Of course, if the NPU used in the heart of a switching/routing system like this can buffer some of the packets during a CAM update, they may not be entirely lost. However, this requires that the long- term average rate at which lookups can be done is greater than the rate at which lookups must be processed. This may not be possible for some applications and line speeds. Now these same 74,400 discarded packets per second will cause their respective Transmission Control Protocol (TCP) sessions (assuming that they belong to typical TCP sessions) to time out because no acknowledgement response will be received at the source to confirm the safe arrival of these packets to their intended destinations. The TCP congestion algorithm specifies that if a TCP time- out occurs, the congestion window must be narrowed down to the size of a single packet. 6,7 This slows down the entire TCP session unbelievably. This is because as a consequence of the narrower conges- tion window, the transmitter at the source must wait for an acknowledgement from the receiver for every packet it sends before it transmits the following packet. This is a subtle, but rather spectacular, indication of how much the management of the search engine tables in the router affects numerous sessions. REPROACHES AGAINST CAM-BASED SEARCH ENGINES We mentioned earlier in this chapter that systems designers in general have a rather negative view of CAMs. 8,9 It is logical to ask how much this view is justified. To find the answer, we will go through some of the major reproaches that the switch/router industry has voiced against