Routing table compaction in ternary CAM

Abstract

Techniques are presented for reducing the size of routing tables stored in ternary content-addressable memory (CAM), which result in decreased cost, power consumption, and thermal dissipation. CAM allows simultaneous comparison between all indexes and the key (the destination IP address), and the entry corresponding to the matched index can be obtained directly. CAM's main advantage is that search time is bounded by a single memory access; thus, it can guarantee high lookup throughput. There are two types of CAM: binary, where each bit position, stores only 0 or 1, and ternary, where each bit position can store 0, 1, or don't care. Ternary CAM (TCAM) could solve the longest-prefix-matching problem more directly than binary CAM. In addition to the index, TCAM also stores a separate mask for each entry. The mask specifies which bits in the index are active, thereby specifying the variable-length prefix.