an efficient hardware-based multi-hash scheme for high speed ip lookup department of computer...
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An Efficient Hardware-based Multi-hash Scheme for High Speed IP Lookup
Department of Computer Science and Information Engineering National Cheng Kung University, Taiwan R.O.C.
Authors: Socrates Demetriades, Michel Hanna, Sangyeun Cho and Rami MelhemPublisher: High Performance Interconnects, 2008. HOTI '08. 16th IEEE Symposium on 26-28 Aug. 2008Present: Chia-Ming ,Chuang Date: 9, 24, 2008
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Outline
1. Introduction 2. Architecture 3. Bit select mechanism 4. Conclusion
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Introduction (1/3)
Ternary Content Addressable Memory (TCAM)
Trie-based schemes Hash-based schemes
Current techniques IP lookup have three categories
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Introduction (2/3)
First hashing can happen collisions and requires resolution
techniques that may result in unpredictable lookup performance
Second hash keys be included “don’t care” bit
Three determine the longest prefix
hash-based IP lookup problem
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Introduction (3/3)
High lookup throughput
• A multiple table , multiple hash functions
• Bit select mechanism high space utilization
• Modified version of the Cuckoo hashing algorithm Low power consumption
• Sum of advantage
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Outline
1. Introduction 2. Architecture 3. Bit select mechanism 4. Conclusion
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Architecture overview (1/4)
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Architecture (2/4)
Based on a multi-level hash table (MHT)
All hash function use the same bit position in a prefix or a
destination address
PS:references [16] S. Cho, J. Martin, R. Xu, M. Hammoud, and R. Melhem, “Ca-ram:A high-performance memory substrate for search-intensive applications,”pp. 230–241, IEEE ISPASS, April 2007.
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Architecture (3/4)
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Architecture (4/4)
Do not classify prefixes based on their lengths Each table is accessed using a hardware based
index generator a number of match processors compare the fetched
keys with the search key in parallel
“Bit-Select” component (1)decides which bits participate in the index generation
(2)“don’t care bits” may appear in the selected bits for indexing
(3)Bit-Select mechanism needs to resolve this by prefix expansion
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Outline
1. Introduction 2. Architecture 3. Bit select mechanism 4. Conclusion
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Bit select mechanism (1/7)
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Bit select mechanism (2/7)
(一 ) Most prefix have lenghts between16 and
24 bits 24 bit prefixes comprise about 54% no prefixes less than 8 bit (二 ) As a study in [9] pointed out, regardless
of prefix length, start from the6th bit and reach the prefixes’ maximum length.
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Bit select mechanism (3/7)
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Bit select mechanism (4/7)(一 ) X-axis =>(Expansion size)/extra provided capacity Y-axis=> unresolved collisions no prefixes less than 8 bit(二 ) From the experiments, we find that any c
onfiguration that can keep the expansion between 20% and 90% of the extra provided capacity results in less than 5% of unresolved collisions.
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Bit select mechanism (5/7)
controlled prefix expansion
controlled wildcard resolution
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Max bucket is 234 itemMax bucket is 49 item
Total 49*3=147Cuckoo hashing algorithm
Bit select mechanism (6/7)
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Bit select mechanism (7/7)(一 ) a collision may appear if an item x can not be inser
ted into tables Ti, i = 1, . . . , d because buckets Ti [hi(x)], i = 1, . . . , d are full.
(二 ) by checking whether an item y at some bucket Ti [hi(x)], 1 ≤ i ≤ d, can migrate to some other table Tj =\ Ti. This requires that a bucket Tj [hj(y)] has an
empty entry to accommodate the item y.(三 ) If such an item y is found, then it can be moved a
nd x will take its place.
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Outline
1. Introduction 2. Architecture 3. Bit select mechanism 4. Conclusion
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Conclusion (1/3)
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Conclusion (2/3)
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Conclusion (3/3)