Bridge Out: Extending RFC 2544 for DCB Devices

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Bridge OutExtending RFC 2544 for DCB Devices

• Timmons C. Player
• David Newman
• IETF BMWG interim meeting, 30 October 2009

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Agenda

• Worlds shortest DCB intro
• Limitations of throughput for DCB
• Limitations of latency for DCB
• Other problems
• New metrics for DCB testing

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Introducing DCB

• DCB (aka DCE, CEE) converges data, storage onto
  single network
• IEEE 802.1Qbb (aka PFC) adds flow control per
  VLAN priority
• Other DCB mechanisms for
• Capabilities exchange (DCBX)
• Congestion notification (802.1Qau)
• Shaping (802.1Qaz)

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Whats wrong with throughput?

• RFC 1242 throughput is fine for Ethernet
• Canonical method Measure oload with 0 loss,
  followed by oload with packet loss
• Highest zero-drop rate is the throughput rate
• This does not work for DCB

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Whats wrong with throughput?

• Loss should never occur with DCB
• Flow control throttles transmitters
• Impossible to have success case, then fail case
• No distinction between iload and oload
• Device that forwards 0 packets could have
  line-rate throughput in DCB context
• No distinction among traffic classes
• Different classes may (and probably will) have
  different maximum forwarding rates

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Whats wrong with latency?

• RFC 2544, section 26.2, requires measurement at
  throughput rate
• Oops There is no throughput rate
• RFC 1242 uses different measurements for
  store-and-forward, bit-forwarding
• Oops DCB devices may alternate modes
• RFC 2544 does not measure per class

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What else can go wrong?

• 2544/2889 tests use lock step pattern
• 1 -gt 2,3,4 2 -gt 3,4,1 3-gt 4,1,2 etc.
• Very regular packet departure intervals

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What else can go wrong?

• DCB devices quickly go out of lock step
• Not just per-port but also per-class
• Much tougher on schedulers

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DCB testing Whats new

• Proposed new work itemhttp//www.ietf.org/id/dra
  ft-player-dcb-benchmarking-00.txt
• New metric Queueput
• Measures MOL per classification
• Multiple queueputs, one per classification, are
  possible
• Maximum forwarding rate
• Same concept as in 2285/2889
• For DCB, more meaningful than throughput
• Extended to measure per classification

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DCB testing Whats new

• Back-off measures DUT PFC overhead
• Conceptually similar to 2544 frame loss test
• Offer traffic above queueput rate then reduce
  iload until the DUT no longer pauses ingress
  traffic
• Measure per classification

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DCB testing Whats new

• Back-to-back
• Conceptually similar to back-off in RFCs
  1242/2544
• Extended to measure per classification
• Other DCB metrics?

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Thanks!

• timmons.player_at_spirent.com
• dnewman_at_networktest.com