Search engines are a key element in various networking systems that use routers, switches, and processors. Typically, these software-based devices require long search times. Their software instructions need a lot of time to perform comparison functions, too. And, they're difficult to implement for "don't care" masks.
Virage Logic Corp. of Fremont, Calif., though, has come up with a hardware approach that lets network lookup tables operate at wire speeds, conducting up to 165 million searches/s. According to the company, this process effectively triples the flow rate of network traffic, compared to software-based and standalone content-addressable memory (CAM) solutions.
Ternary CAMs that allow the storage of "0," "1," and "don't care" logic states are key to the approach. The CAMs are used in the company's Custom-Touch NetCAM compiler, which can be embedded into IC designs for network applications. The compiler permits the delivery of completely characterized timing and power information. Designers, then, have the flexibility to make tradeoffs at any time during the design cycle, enabling optimal circuit performance (see the figure).
"CAMs have emerged as the search engines of choice because of their ability to conduct high-speed table lookups that are required to meet the demands of ever-growing traffic on the Internet," according to Krishna Balachandran, director of product marketing at Virage.
To get up to a fivefold speed increase over standalone CAMs, the compiler implements a part-matched scheme. The scheme integrates or "matches" the CAM, SRAM, and additional special-purpose logic efficiently during the design's layout phase. Part matching involves matching the routing pitches on all the blocks. It also uses fewer interconnects between components. As a result, the scheme reduces wire delays and overheads associated with longer wires.
Unlike standalone CAM/SRAM subsystems, an embedded CAM subsystem experiences no I/O pad and board wire delays. This produces higher speeds. Embedded CAMs also can be cascaded in order to build larger table sizes or to widen the search bandwidth, resulting in a higher throughput.
The NetCAM compiler generates synchronous, single-port, ternary CAMs that are equipped for pattern searches. CAMs generated by the compiler can range in size from 1 to 32 kbytes. Word widths can extend to 64 bits.
Custom-Touch NetCAM is available on TSMC's 0.18-µm process. A single, node-locked compiler that can generate any configuration can be licensed for $750,000. A single-configuration version costs $200,000.
For more information, contact Virage Logic at (510) 360-8000. Or, go to www.viragelogic.com.