tern, and a together with the ternary encoding of data in the memory array critical capabilities for This combination of partial bit matches to be extracted. These are obviously 3 and 4. making result, depending on the CAM design, can be produced single output burst (for of exam- suc- complete classification ranges and routing decisions involving functionality at layers as a ple, the result of example, in order of priority) for subsequent processing is by 24 bits wide. Other The search the highest priority). In the case of multiple hits, it can be produced as the a system. The cessive results shown (for from the Kawasaki LSI 9.4Mb CAM has an output port 32 that bits wide. example CAMs, smaller ones (1Mb/2Mb), have an output port that is a especially and control signals available on a typical CAM usually show the status These of signals the various also Special the flag and denote the type of the search result (single or multiple for hit). different vendors) in banks of array of multiple identical devices (at different levels of depth without incurring allow a chain the as cascading a handy way to increase the size of the lookup tables, in many cases a Downloaded from Digital Engineering Library @ McGraw-Hill reserved. Copyright Anv use is subject to the Terms of Use as given at the © 2004 The McGraw-Hill Companies. All rights website. SEARCH ENGINES SEARCH ENGINES 223 Tag bits Source address 1 Destination address 1 Source address 2 Destination address 2 Source address 3 Destination address 3 Source address 4 Destination address 4 Source address 5 Destination address 5 Classification table Source address 6 Destination address 6 Destination address 1 Destination address 7 Destination address 8 Destination address 9 Destination address 10 Forwarding table FIGURE 12.2 The concept of tag bits to improve the use of CAM. (Source: NetLogic Microsystems) performance penalty in search time. For instance, our example of the Kawasaki LSI 9.4Mb CAM can be cascaded up to eight pieces with other CAMs without any glue logic and 