DATA CENTER TO THE HOME

Transcription

1 DATA CENTER TO THE HOME Koen De Scheer, Inton Tsang. Olga Bondarenko. Bob Briscoe. March, 015 1

2 DCttH OBJECTIVE: UNIVERSAL SUPPORT FOR LOW LATENCY = SUPPORT FOR ADAPTIVE INTERACTIVE APPLICATIONS RGW UNManaged Network Service LL Service

3 INTERACTIVE APPLICATIONS on the INTERNET? Home Access Cloud Reno Cubic RGW Reno/Cubic Frontend Server Back-end Server Back-end Server Cubic Back-end Server Reno Large queues for high throughut and low dro = Poor Latency ECN = No dro ECN++ = Small queues = Bad for interactive alications = Low latency & High throughut 3

4 DATACENTER to the HOME? Home Access Cloud Reno Cubic RGW Reno/Cubic Frontend Server Back-end Server Back-end Server Cubic Back-end Server Reno Windows and Linux 3.18 have imlementations ready Clients use Reno and Cubic Can t use without causing trouble Public Internet does not suort available on Windows Server and Linux 3.18 used internally in the data center 4

5 MIGRATION OBJECTIVE: LOW LATENCY ACCESS TO THE CLOUD, EQUAL STEADY STATE THROUGHPUT TO RENO/CUBIC Can be used as Low Latency congestion controller? Reno LL AQM LL AQM RGW LL Service Cubic Which AQM to be deloyed on queuing bottlenecks? Suort migration! 5

6 LOWER LATENCY BY SMARTER USE OF ECN DATA CENTER TCP TCP (Reno) Resonse to congestion in sender Half the congestion window when dro detected in one RTT Reduce artially er marked acket; half if all marked in one RTT React according to level of congestion Echo Congestion Exerienced (CE) until sender acknowledges Congestion Window Reduced (CWR) ECN feedback in receiver Echo marking state of received ackets without acknowledgement accurate ECN feedback Smooth and delay a dro or mark to allow bursts ECN marking in network Don t smooth or delay queue size Shallower marking threshold immediate ECN marking 6

7 DEMONSTRATED ON A REAL BB RESIDENTIAL TESTBED Alcatel-Lucent 730 Alcatel-Lucent 7750 RTT = 8ms xdsl VLAN be VPRN 40ms xdsl VLAN fr 7

8 LOWER LATENCY BY SMARTER USE OF ECN DATA CENTER TCP TCP (Reno) AQM configuration Pdf in 50s interval [%] Average Q size Q size variation q size [ackets] dctc 5 Instant Q size Measured in a BB DSL testbed RTT = 8 ms (unloaded) BW = 40 Mbs (downstream) 1 steady state flow running alone Reno/Cubic/ = Linux kernel

9 QUEUE SIZE AT DEQUEUE 1 TCP RENO FLOW (STEADY STATE) Pdf [%] Average Q size dctc q size [ackets] Pdf in 1s interval [%]

10 QUEUE SIZE AT DEQUEUE 1 FLOW (STEADY STATE) Pdf [%] Instant Q size dctc q size [ackets] Pdf in 1s interval [%]

11 DOES NOT WORK ON TRADITIONAL RED-ECN Single Q Reno Cubic RED AQM dc 11

12 SEEMS TO WORK ONLY IN THE DATA CENTER Single Q HIGH dro continuous FULL queues Reno Cubic RED AQM dc 1

13 THROUGHPUT: Cubic (= Reno) flows: flows: 0 RTT = 8 ms (unloaded) BW = 40 Mbs (downstream) BDP = 7 full sized ackets AQM = RED with recommended configuration* X-axis: 0 50 sec Y-axis: first row: 0 (80 / <nbr_flows>) Mbs Y-axis: other rows 0 (80 / <nbr_dctc>) Mbs * tc qdisc add dev eth root red limit min max avkt 1000 burst 0 ecn bandwidth 40Mbit 13

14 Q SIZE PDF: Cubic (= Reno) flows: flows: 0 RTT = 8 ms (unloaded) BW = 40 Mbs (downstream) BDP = 7 full sized ackets AQM = RED with recommended configuration* X-axis: ackets (450 Kbytes, 90 ms) Y-axis: autoscale count ackets * tc qdisc add dev eth root red limit min max avkt 1000 burst 0 ecn bandwidth 40Mbit 14

15 AQMS FOR EQUAL STEADY STATE RATE MIGRATION PATH FOR NEW CC SCHEMES How should an AQM guarantee an equal steady state rate for flows with different congestion control schemes classify ackets according to CC schemes align the dro/mark robabilities TCP Reno AQM? TCP Reno 15

16 TCP CONGESTION CONTROL SCHEMES STEADY STATE RATE Steady state rate has been calculated for existing CC schemes: r 1 1. RTT r cubic RTT r dc RTT 16

17 TCP CONGESTION CONTROL SCHEMES STEADY STATE RATE Steady state rate has been calculated for existing CC schemes: r 1 1. RTT r cubic RTT r dc RTT But we calculated that running in non-on/off mode behaves as: r dc_ RTT 17

18 TCP CONGESTION CONTROL SCHEMES FAIRNESS BETWEEN AND RENO Mark/dro robability relation for equal rate and RTT: r r dc RTT RTT dc 1 1. RTT dc RTT dc dc

19 TCP CONGESTION CONTROL SCHEMES FAIRNESS BETWEEN AND RENO Mark/dro robability relation for equal rate and RTT: r r dc RTT RTT dc 1 1. RTT dc RTT dc dc 1.63 P f Square is easy! Comare Q size with random variables (Q) Random() P (Random() P) &&(Random() max( Random(), Random()) P P) 19

20 BEHAVES EXACTLY AS RENO IF WE CORRECTLY CORRELATE MARKING AND DROPPING ECN Classifier Single Q Reno Cubic* dc 1.63 Couled AQM * Under local DC-access conditions (small BDP) Cubic behaves as Reno Instant Q size Sloe starts from the origin to avoid ON/OFF behavior in steady state 0

21 BEHAVES TOO EXACTLY AS RENO ECN Classifier Works Single Q No Latency gain Reno Cubic dc 1.63 Couled AQM Instant Q size 1

22 DUAL QUEUE LOW LATENCY Dual Q ECN Classifier AQM? Scheduler? TCP_ r r dc 1. dc RTT RTT dc dc 8

23 DUAL QUEUE LOW LATENCY Dual Q ECN Classifier AQM? Strict Priority TCP_ 1/5 = 8 ms /(8 + 3) ms r r dc 1. dc RTT RTT dc dc 8 = 5 3

24 DUAL QUEUE LOW LATENCY Dual Q ECN Classifier 1 Strict riority scheduler TCP_ Reno Cubic dc 8 Couled AQM Instant Q time 4

25 DUAL QUEUE LOW LATENCY Dual Q ZERO Q latency ECN Classifier 1 Strict riority scheduler dc 8 TCP_ Couled AQM Reno Cubic Instant Q time Measure Q in time is imortant for otimal fairness! 5

26 THROUGHPUT: Cubic (= Reno) flows: flows: 0 RTT = 8 ms (unloaded) BW = 40 Mbs (downstream) BDP = 7 full sized ackets AQM = DualQ Couled X-axis: 0 50 sec Y-axis: all rows: 0 (80 / <nbr_flows>) Mbs

27 Q SIZE PDF: Cubic (= Reno) flows: flows: 0 RTT = 8 ms (unloaded) BW = 40 Mbs (downstream) BDP = 7 full sized ackets AQM = DualQ Couled X-axis: ackets (450 Kbytes, 90/w ms) Y-axis: autoscale count ackets

28 THROUGHPUT RATIO (CUBIC / ) RED AQM Cubic Cubic DualQ Couled AQM 8

29 DETAILED IMPLEMENTATION 3 arameters: Reno sloe (bits) Q d >T dc (Q r <<S d ) > R1 Reno Cubic sloe (bits) threshold (Q size) Dctc QSize R1 ECN Classifier ECN marker 1 Strict riority scheduler TCP Reno Dro dc 8 Reno QTime r (Q r <<S r ) > R1 && R R1 R S r S d 3 Q r && = 9

30 ADAPTIVE INTERACTIVE APPLICATIONS Panoramic interactive video C-AQM Adative Low latency encoder/decoder Video/Voice conferencing User interaction C-AQM Remote control,... 30

31 FUTURE WORK & CONCLUSIONS? Dynamic behaviour to be investigated (exected to be 5x better due to 5x latency reduction) Unmanaged Low Level network Service Native suort for Adative Interactive Alications Better usage for ECN (marking can be more often than droing) x/ relation for ECN based congestion controller (x determining the marking rate) ² relation between mark and dro in AQM Backwards comatible: should resond to dro as Reno Currently 3.18 Linux imlementation fails on this asect Steady state throughut fairness between and Reno Cubic Only if flows are terminated to nearby (local) datacenter If longer RTT, flows are getting lower throughut than Reno Cubic Reno Cubic fallback if throughut is too low and base RTT is too long? Define a TCP congestion controller which is less (/not) deendent on the RTT? 31

32 Questions 3

33 BASE RTT FAIRNESS WHAT IF THE DATACENTER IS FURTHER OR CLOSER Throughut ratio (Reno / ) Further DC: U to 5 times less throughut for RTT [ms] Closer DC: Fast growing advantage for Not to be used Couled AQM configured for 10ms base RTT and 40ms Reno queue time (1/5 RTT ratio) 33

34 STEADY STATE THROUGHPUT WITH SLOPE-RED W W 1 Per long RTT: (1) W W1 And also er RTT: () W In steady state if (1) is comensated so from () if (3) g g As, if is stable in steady state (4) r W rtt The instantaneous rate (5) thus (3,4,5) W 1 1 W 1 W 1 r rtt 1 W 34

35 QUEUE SIZE BASED COUPLED AQM 3 arameters: Reno sloe (bits) Q d >T dc (Q r <<S d ) > R1 sloe (bits) threshold (Q size) Dctc QSize R1 ECN Classifier TCP Reno ECN marker Dro %/10% Weighted Round Robin dc 8 Reno QSize r (Q r <<S r ) > R1 && R R1 R S r S d 3 Q r && = 35

36 QUEUE SIZE BASED COUPLED AQM THROUGHPUT RATIO (CUBIC / ) Cubic Cubic Qtime - DualQ Couled AQM Qsize - DualQ Couled AQM 36