Bridge Out:Extending RFC 2544 for DCB

Devices

Timmons C. PlayerDavid Newman

IETF BMWG interim meeting, 30 October 2009

Agenda

• World’s shortest DCB intro• Limitations of throughput for DCB• Limitations of latency for DCB• Other problems• New metrics for DCB testing

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)

What’s 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

What’s 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

What’s 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

What else can go wrong?

• 2544/2889 tests use “lock step” pattern

• 1 -> [2,3,4]; 2 -> [3,4,1]; 3-> [4,1,2]; etc.

• Very regular packet departure intervals

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

Traffic classXOFF/XON

interval (µsec)Inter-PFC burst interval

(µsec)

P1 200 500

P2 150 450

P3 300 700

DCB testing: What’s new

• Proposed new work item:http://www.ietf.org/id/draft-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

DCB testing: What’s 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

DCB testing: What’s new

• Back-to-back– Conceptually similar to back-off in RFCs

1242/2544– Extended to measure per classification

• Other DCB metrics?

Thanks!

• timmons.player@spirent.com• dnewman@networktest.com