ABSTRACT

The structure of Content-address memory (CAM) is similar to that of the normal Random access memory (RAM) but has an additional circuit for its operation of comparison. Vendors aim to develop their CAM devices with a variety of features. The conventional CAMs are binary, in which each cell can take two logic states: 0 and 1. Binary CAM performs exact-match searches, whereas a ternary CAM (TCAM) allows pattern matching with the use of “do not care” (X). In TCAM, each bit of the incoming data is compared with the same position bit of the stored data, and the result is the address of the memory location where the match passed. TCAM uses data as the search key and returns the matching physical address(es), and the priority encoder can only uses the physical address(es) to find the “highest priority” entry in TCAM. TCAM table update caused by routing information modification is simply similar to that of the conventional TCAM-based lookup mechanisms.