Hash and Stuffing: Overlooked Factors in Network Device Benchmarking - PowerPoint PPT Presentation

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Hash and Stuffing: Overlooked Factors in Network Device Benchmarking

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  1. Hash and Stuffing:Overlooked Factorsin Network Device Benchmarking • David Newman • Timmons C. Player

  2. Agenda • What it is • What it isn’t • Addresses and hashing • Bit- and byte-stuffing • Tentative workplan

  3. What it is • http://www.ietf.org/internet-drafts/draft-ietf-bmwg-hash-stuffing-00.txt • An attempt to deal with the contents of test traffic • A long application note • Covers use of BMWG methodologies(especially results reporting)

  4. What it isn’t • Attempt to define every possible factor affecting test results • Not terminology • Not methodology

  5. Addresses and hashing • BMWG methodologies do not require declaration of addresses used in test traffic • Because of hashing algorithms, addresses can have a huge impact on test results • Leads to non-repeatability • We need to characterize the effects of addresses and compensate for these effects


  6. Simple example • Many test instruments generate source MAC addresses ending in “:01” • Many switches hash on low-order 3 bits • Uh-oh...

  7. Simple example ingress || \/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ___ ___ ___ ___ ___ ___ ___ ___ | || | | | | | | | | | | | | | | | | ||NP0| |NP1| |NP2| |NP3| |NP4| |NP5| |NP6| |NP7| | ||___| |___| |___| |___| |___| |___| |___| |___| | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ || \/ egress

  8. Proposed solution • 001^001 = 000 and congestion • RRR^RRR = RRR and no congestion, where R = pseudorandom value • We propose 00:PP:PP:RR:RR:RR, wherePP:PP = port number (00:01-FF:FF)RR:RR:RR = pseudorandom value • We also discuss hashing issues at L3 and L4

  9. Stuff bits and bytes • On bit-synchronous links (DS-1, DS-3, etc.), PPP adds an escape bit prior to any sequence of five “1” bits in a frame • On byte-synchronous links (POS), PPP adds escape bytes for up to 34 different control characters

  10. So what? • Stuffing adds significant and variable overhead • An intended load of 90 percent could be an offered load of 110 percent…oops • We should never congest the DUT/SUT for latency or throughput measurements • We need to characterize and compensate for the effects of stuffing

  11. Proposed solution • For bit stuffing, we offer formulas for determining the probability of stuff bits in infinite and finite strings of bits • For byte stuffing, we offer probabilities for stuffing both with and without ACCM (async-control-character map)

  12. Proposed workplan • August 2004: Initial draft 00 • 31 August 2004: Acceptance (or otherwise) for BMWG review • 15 October 2004: Draft 01 • December 2004: Draft 02 • February 2005: Move for last call