Bridge Out: Extending RFC 2544 for DCB Devices Timmons C. Player David 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 class XOFF/XON interval (µsec) Inter-PFC burst interval (µsec) P P P

DCB testing: What’s new Proposed new work item: 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!