Error Tolerant and Performance Enhanced TCAM for Network Applications

Abstract: Content Addressable Memory (CAM) is a type of solid-state memory in which data are accessed by their contents rather than physic al locations. Ternary Content Addressable Memories (TCAMs) are special memories which are widely used in high-speed network applications such as routers, firewalls, and network address translators. In high- reliability network applications such as aerospace and defense systems, soft-error tolerant TCAMs are indispensable to prevent data corruption or faults caused by radiation. The proposed work uses a novel soft-error tolerant TCAM for multiple-bit-flip errors using partial keys and parity based logic for search time reduction. The proposed TCAM corrects multiple bit-flip errors and enhances the tolerance of the TCAM against soft errors. TCAM detects multiple- bit-flip errors by the generated X-keys using the X look-up. If the keys match the different locations, then a soft error is suspected and TCAM refreshes the TCAM words by using the backup ECC-SRAM. The proposed CAM also uses parity an extra one-bit segment, derived from the actual data bits. We only obtain the parity bit, i.e., odd or even number of “1”s. This additional parity bit reduces the sensing delay and boosts the driving strength of the 1-mismatch case by half. The hardware overhead of the proposed TCAM is small due to the use of a single TCAM. The parity based TCAM can be easily implemented and is useful for fault-tolerant packet classifiers.

Keywords: TCAM, Multi-bit errors, ATM, SRAM, Parity