Longest Prefix Match Engine Using Prefix Bitmap Scheme
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Solution Overview
Problem
Current longest prefix match (LPM) search engines face challenges with TCAM-based solutions being expensive and power-hungry, while SRAM/DRAM-based algorithmic schemes are complex in hardware and software management, and existing solutions are inefficient in terms of silicon area and power consumption.
Innovation Solution
A LPM search engine is developed using a combination of exact match (EXM) engines with a prefix bitmap scheme and a moderately sized TCAM, allowing each EXM engine to cover multiple consecutive prefix lengths, reducing quantization loss and hardware/software complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TCAM-based LPM search engines are used, then search speed and capacity are improved, but cost and power consumption increase significantly
Solution Approach 1:
The patent segments the LPM search function into multiple components: a TCAM for storing prefix entries, an EXM engine for exact match operations, and a prefix bitmap for tracking prefix lengths. This segmentation allows each component to perform a specialized function, reducing the overall power consumption compared to using a full TCAM for all operations while maintaining high search speed.
Solution Approach 2:
The patent introduces a dynamic prefix bitmap that tracks which prefix lengths are present in the TCAM. This dynamic structure allows the EXM engine to efficiently determine the longest prefix match by checking only relevant prefix lengths, reducing unnecessary comparisons and power consumption while maintaining fast search performance.
2Productivity
If TCAM-based LPM search engines are used, then search speed and capacity are improved, but device cost increases
Solution Approach 1:
The patent segments the LPM search function into multiple components: a TCAM for storing prefix entries, an EXM engine for exact match operations, and a prefix bitmap for tracking prefix lengths. This segmentation allows each component to perform a specialized function, reducing the overall cost compared to using a full TCAM for all operations while maintaining high search speed.
Solution Approach 2:
The patent introduces an EXM engine as an intermediary between the TCAM and the output. The EXM engine handles exact match operations that would otherwise require additional TCAM resources, reducing the TCAM size requirement and overall device cost while maintaining fast search performance through the coordinated operation of multiple components.
3Area of stationary object
If SRAM/DRAM based algorithmic search schemes are used, then silicon area and power consumption are reduced, but hardware and software complexity increases
Solution Approach 1:
The patent segments the search function into specialized components (TCAM for prefix storage, EXM engine for exact matching, prefix bitmap for length tracking), allowing each to be optimized independently. This segmentation reduces overall hardware complexity compared to a monolithic algorithmic approach while maintaining area efficiency through the use of SRAM/DRAM for the EXM engine and prefix bitmap.
Solution Approach 2:
The patent implements a self-service mechanism where the prefix bitmap automatically tracks which prefix lengths are present in the TCAM, and the EXM engine automatically determines the longest prefix match by checking the bitmap. This automation reduces software management complexity compared to manual TRIE-based approaches while maintaining area efficiency.
4Area of stationary object
If SRAM/DRAM based algorithmic search schemes are used, then silicon area and power consumption are reduced, but ease of operation deteriorates
Solution Approach 1:
The patent implements a self-service mechanism where the prefix bitmap automatically tracks which prefix lengths are present in the TCAM, and the EXM engine automatically determines the longest prefix match by checking the bitmap. This automation reduces software management complexity compared to manual TRIE-based approaches while maintaining area efficiency.
Solution Approach 2:
The patent introduces a prefix bitmap as an intermediary data structure that simplifies the interaction between the TCAM and EXM engine. This intermediary automatically manages prefix length information, reducing the software management burden compared to direct TRIE-based approaches while maintaining area efficiency through SRAM/DRAM implementation.
Data Source
AI summary
A LPM search engine includes a plurality of exact match (EXM) engines and a moderately sized TCAM. Each EXM engine uses a prefix bitmap scheme that allows the EXM engine to cover multiple consecutive prefix lengths. Thus, instead of covering one prefix length L per EXM engine, the prefix bitmap scheme enables each EXM engine to cover entries having prefix lengths of L, L+1, L+2 and L+3, for example. As a result, fewer EXM engines are potentially underutilized, which effectively reduces quantization loss. Each EXM engine provides a search result with a determined fixed latency when using the prefix bitmap scheme. The results of multiple EXM engines and the moderately sized TCAM are combined to provide a single search result, representative of the longest prefix match. In one embodiment, the LPM search engine supports 32-bit IPv4 (or 128-bit IPv6) search keys, each having associated 15-bit level 3 VPN identification values.