A LowPower Network Search Engine Based on Statistical Partitioning

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A Low-Power Network Search Engine Based on
Statistical Partitioning

• Taskin Kocak and Faysal Basci
• Dept. of Electrical and Computer Engineering
• University of Central Florida, Orlando, FL 32816
• tkocak_at_cpe.ucf.edu

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Introduction

• Stringent memory access and search speed
  requirements are two of the main bottlenecks in
  wire speed packet processing.
• Most viable search engines are implemented in
  Content Addressable Memories (CAM).
• In networking applications, CAMs are generally
  used in VLAN
• lookup tables (layer-2), packet forwarding lookup
  tables (layer-3), session lookup table (layer-4)
  and filtering (layers 5-7)
• CAMs have high operational speed advantage over
  other memory search algorithms, such as
  look-aside tag buffers, binary or tree based
  searches.
• However, this performance advantage comes with a
  price of higher silicon area, and higher power
  consumption (3-5 W/chip).

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CAM Architecture
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TCAMs in IP forwarding

• TCAMs dont care storage capability is
  favorable in lookup engines.
• e.g., for a 24-bit prefix, the last 8 bits will
  be x
• Routing table entries stored in TCAMs are
  ordered according to their prefixes
• In the case of multiple matches priority encoder
  will choose the one with the lowest address,
  which is the longest matching prefix

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32-bit IP Prefix Distribution
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Partitioned TCAM
Perform a search in TCAM1 If there is a match
DONE otherwise search TCAM2 If
there is a match DONE otherwise
issue mismatch end
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Power Consumption
PTCAM PSTATIC PCLOCK PMATCH PMISS
PX Here, we are concerned about the dynamic power
consumption caused by the search (comparison)
operation.
where ? represent the probability that a match
will occur in TCAM1
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Experimental Results dynamic power
Example TCAM circuit is implemented in Cadence
for TSMC 0.18-µm CMOS. Simulations are run at 100
MHz. PMATCH 397 nW PMISS 515 nW Px
336 nW
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Experimental Results dynamic power
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Dynamic power
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Power consumption with different miss rates for
Telstra
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Experimental Results powerlatency
EL2-?0 L search latency in clock cycles
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Experimental Results
Expected power savings and average latency when
partitioning into three TCAMs
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Reconfigurable Architecture
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Conclusions

• We presented a TCAM partitioning scheme, which
  utilizes statistical distribution of prefixes.
• We showed that indeed the partitioning helps
  reducing the power consumption in IP lookup
  applications.
• Partitioning into two and three, reduce power
  consumption considerably, whereas further
  partitioning shows little improvement

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ANCHOR workshop at ISCA 2004