PCAM: a ternary CAM optimized for longest prefix matching tasks

Abstract

An optimized ternary CAM concept is introduced for application in the longest prefix matching tasks of the Internet search engines. It employs w+1 RAM bits for a word of size w. A conventional TCAM needs 2w RAM bits for the same word size. Based on this concept an 8 bit prefix-CAM cluster is designed out of 9 SRAM bits, four of which merge to store a 32-bit IPv4 prefix. A complete prefix-CAM module employs 22% less transistors than a conventional TCAM, for equal storage size and equal functionality. We confirm the 22% area saving by implementing the layouts for prefix-CAM and TCAM words. Our design also reduces interconnect area by reducing address decode lines.