A fast ternary CAM design for IP networking applications

Bruce Gamache, Z. Pfeffer, S. Khatri
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引用次数: 29

Abstract

In this paper we describe a VLSI implementation and complete circuit design of a fast ternary CAM (TCAM). TCAMs are commonly used to perform routing lookups in the backbone of IP networks and small gateways. Our TCAM is designed to have a greater capacity and speed than any commercial offering at this time. In contrast with existing TCAM approaches, our TCAM allows complete flexibility in the location where any new entry is inserted. This is achieved by a novel longest prefix match (LPM) determination circuit, whose delay increases logarithmically with the number of bits to be looked up. We have implemented our TCAM with 512 bits of prefix entry with 512 bits of destination information, allowing it to implement large address lookups as well as quality of service mechanisms. This would make our TCAM design particularly suitable for IPv6 routing lookup applications. The speed improvement of our TCAM over currently available TCAMs results from various carefully selected VLSI architectural and implementation choices. The TCAM size is 21 Mb and is broken up into a regular grid of 13x13 smaller TCAM blocks for improved speed characteristics. Routing lookup operations use a heavily pipelined approach for maximum throughput, while ensuring a lookup latency of 3 clock cycles. Individual match lines in these blocks are split into 4 sections to reduce RC delay in the lookup process. Our LPM determination circuit is implemented using an efficient wired-NOR circuit for further reduced delay. Sense amplifiers are utilized in the LPM and SRAM sections of the TCAM and are located in the center of each TCAM subblock in order to improve lookup speed. We have implemented and validated our design using state-of-the-art circuit analysis and design tools. We have also generated mask layouts of the entire TCAM design using current layout tools. The complete TCAM circuit design is approximately 18mm on a side, with a total capacity of 21Mb. Our TCAM has an ability to perform routing lookups at a line rate of 76.8Gb/s which is twice as fast as the fastest commercially available TCAM today.
IP网络应用的快速三元CAM设计
本文描述了一种快速三元凸轮(TCAM)的VLSI实现和完整电路设计。tcam通常用于在IP网络骨干和小型网关中执行路由查找。我们的TCAM设计具有比目前任何商业产品更大的容量和速度。与现有的TCAM方法相比,我们的TCAM在插入任何新条目的位置上具有完全的灵活性。这是通过一种新颖的最长前缀匹配(LPM)确定电路实现的,其延迟随着要查找的比特数呈对数增长。我们已经用512位的前缀条目和512位的目的地信息实现了TCAM,允许它实现大型地址查找和服务质量机制。这将使我们的TCAM设计特别适合IPv6路由查找应用程序。我们的TCAM比目前可用的TCAM速度提高的结果是各种精心挑选的VLSI架构和实现选择。TCAM大小为21 Mb,并被分解为13x13个较小的TCAM块的规则网格,以提高速度特性。路由查找操作使用高度流水线的方法来获得最大吞吐量,同时确保查找延迟为3个时钟周期。这些块中的单个匹配行被分成4个部分,以减少查找过程中的RC延迟。我们的LPM确定电路采用高效的有线nor电路实现,以进一步降低延迟。在TCAM的LPM和SRAM部分使用感测放大器,并位于每个TCAM子块的中心,以提高查找速度。我们使用最先进的电路分析和设计工具实现并验证了我们的设计。我们还使用当前的布局工具生成了整个TCAM设计的掩模布局。完整的TCAM电路设计单侧约为18mm,总容量为21Mb。我们的TCAM能够以76.8Gb/s的线路速率执行路由查找,这是目前最快的商用TCAM的两倍。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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