1. Student:Shih-Chiang Tsao Advisor:Ying-Dar Lin Date:2007/12/12 Dissertation Fairness Controls for TCP-equivalenceat Endpoint and Request-Response Schedulingat Gateway Where are bottlenecks? What kind of fairness? How and where to control it?

2. 2 /48 2007/12/12 Bottlenecks for the Internet Traffic EDU 2 ISP 2 ISP 1 EDU 1 ER S Internet D2D2 D1D1 ER GIGI GUGU GUGU H1H1 H1H1 HnHn HnHn Intranet Public Fairness Private Fairness IssuePromoted conceptCriterionSchemes Public Fairness TCP-friendliness (TCP-compatibility) <= TCP’s bandwidthAIMD in TCP Private Fairness Class-based weighted fairness Bw 1 :Bw 2 =Weight 1 :Weight 2 Packet scheduling R ER: edge router G I : ISP-side gateway G U :User-side gateway H i, S, D 1, D 2 : End Points

3. 3 /48 2007/12/12 Public Fairness Control at End Point Motivation:  New rate control for Streaming Objective:  Smoothness  Fairness with TCP R1R1 S1S1 Internet R2R2 S2S2 E E E RR Data Streaming TCP ??? Trans. RateTrans. DirectionInstanceTolerable Start-up latency UnconstrainedSimplexOn-demand Video<5 sec Constrained SimplexLive broadcast<5 sec InteractiveVideo conference<0.5 sec Classification of Internet Streaming Seq. No. Time Start-up Latency received playing Late packets Because of the oscillatory rate of TCP

4. 4 /48 2007/12/12 Private Fairness Control at Gateway Internet GUGU GIGI W1W1 W2W2 G G W3W3 user-side access gateway H1H1 HnHn Queuing packets ISP-side edge gateway Motivation : Scheduling packets fails to allocate downlink bandwidth at G I Scheduling requests to manage the responses Objectives: Weighted fairness Shared bandwidth Full link utilization Short transmission time Uplink requests -> <- Downlink responses the IP addresses of H i ’s are hidden in packets Favorable place by enterprises

5. 5 /48 2007/12/12 Related Work and Research Road Map Fairness Private Fairness - Weighted Fairness [PG93] - Class-based [FJ95] Packet Scheduling -WFQ [PG93] -WRR/ DRR [SV96] -SCFQ [GOL94] -SFQ [GVC96] Pre-order DRR (Computer Networks) Public Fairness - TCP-friendliness [FF99, BCC98] - TCP throughput eq [PFT98, AAB05] - Internet Conditions [ZDP01][JID04] TCP-friendly Schemes - GAIMD [YL00] - TFRC [FHP00] - TEAR [ROY00] - SQRT, IIAD [BB01] - SIMD [JGM03] 2. WARC (To be submitted to IEEE Trans. on Computer) Evaluation - Survey [WDM01] - Dynamic Cond. [BBF01] - TFRC’s analysis [VB05] 1. Taxonomy & Evaluation (IEEE Network, Nov. 2007) Request Scheduling - web server [PBB98, BBK00, CP99] - web-side gateway [CCC02, CC01, LGC01] - user-side gateway 3. Minimum-service first request scheduling (Submitted to Computer Networks) Utilization of high BW*delay path High-speed TCP Bandwidth -HS-TCP [SF03] -FAST [JLH07,TWH05] -XCP [KHR02] -VCP [XSS05] DCCP [KHF06] Protocol Versions of TCP -Vegas [BP95] -Improvement [YCC06] Wireless 802.11e, 802.11s Load Balance On-the-fly TCP Path Selection (Computer Comm.) TCP-friendly AQM -Survey [CLB04] -WARD [YCC07]

6. Taxonomy and Evaluation of TCP-friendly Rate-Control Schemes on Fairness, Aggressiveness, and Responsiveness Why do TCP-friendly Schemes have throughput unequal to TCP’s?

7. 7 /48 2007/12/12 3 Criteria for 8 TCP-friendly Schemes CriterionPremise Proper behaviors for a scheme Steady-stateTransient-state FairnessAggressivenessResponsiveness TCP-compatibility Identical network conditions Less bwDon’t careAs fast as TCP TCP-equivalence Equal bwAs fast as TCP TCP equal-share Identical bottleneck Taxonomy Evaluation SchemeFull NameParametersRef. GAIMDGeneral additive inc./multiplicative-dec.α=0.2, β=0.125[YL00] IIADInverse-inc./additive-dec.α=1.0, β=0.67, k=1, l=0[BB01] SQRTSquare-root inc./dec.α=1.0, β=0.67, k=0.5, l=0.5[BB01] SIMDSquare-inc./multiplicative-dec.β=0.0625, k=-0.5, l=1[JGM03] AIAD/HAdditive inc./dec. with historyβ=0.25, k=0, l=0[JGM03] TFRCPTCP-friendly rate control protocolInterval=5 seconds[PKT99] TFRCTCP-friendly rate controlThe number of samples=8[FHP00] TEARTCP-emulation at receiverThe number of samples=8[ROY00] More realistic Influenced by AQM

8. 8 /48 2007/12/12 Fairness Policy In steady-state how a scheme control a flow to use the equivalent bandwidth as a TCP flow? Rate=1/(the time between packets) Estimates the recent TCP throughput during the connection. Repeatedly adjust the sending rate by the estimation TFRC,TEAR, TFRCP Rate Time (s) x x x Rate-based (RB) short-term TCP’s mean rate x Update CWND by a set of control parameters Specific relations between the parameters GAIMD, SQRT, IIAD, SIMD, AIAD/H Long-term Fair  E[T WB ]=f(p, RTT, a,b,k,l..)  E[T TCP ]=f(p, RTT, α= 1, β= 0.5)  E[T WB ]=E[T TCP ] Window-based (WB) Cong. Window (CWND) Time (RTT) x x x x x packet loss event x x x x x long-term TCP’s mean rate

9. 9 /48 2007/12/12 Aggressiveness Policy How a scheme increases the throughput of a flow before encountering the next loss behavior between two losses Sub-linearLinearSuper-linear Step/ proportion of each inc. Non-historicalGAIMDTFRCP HistoricalSQRT, IIADAIAD/H TEAR, TFRC SIMD Tradeoff between aggr. & smoothness Aggressive but not smooth Smooth but not aggressive CWND Time Tradeoff CWND Time Slow at beginning and Fast if no loss occurs for long time Sub-linear CWND Time Super-linear

10. 10 /48 2007/12/12 Responsiveness Policy How a a scheme decreases the throughput of a flow when the loss condition becomes severe Non-historyHistory FixedVariable IIAD, AIAD/HTFRC, TFRCP, TEARGAIMD, SQRT, SIMD -Historical scheme is adaptive for wider network conditions -Fixed-history scheme have fast responsive behavior Tradeoff between resp. & smoothness Discard Out-of-bound history Responsive but not smooth Smooth but not responsive CWND Time Tradeoff Loss rate Time Tx. Rate Time Fixed Loss rate Tx. Rate Time Variable

11. 11 /48 2007/12/12 Evaluations FairnessAggressiveness/ Responsiveness TCP-equivalence (Identical loss condition, artificial loss link) - Change loss rate - Change loss variance Two-states TCP equal-share (Identical bottleneck, dumbbell topology) RTT- heterogeneousOn/Off CBR SDR1R1 R2R2 100Mbps 2ms 100Mbps 30 ms Discarding packets by math model TimeX X X Inter-loss loss R1R1 S1S1 SnSn R2R2 Drop-Tail n TCP-friendly senders 2n Mbps 10ms S’ 1 S’ n n TCP senders D1D1 DnDn D’ 1 D’ n 100 Mbps 20ms on average Artificial loss link Dumbbell topology

12. 12 /48 2007/12/12 Losses in the Internet Different trend Losses in the Internet [ZDP01] TCP-equivalence as CV[T]=0 T: the time between two losses CV[T]: the coefficient-of-variance of T Fairness Test for TCP-Equivalence: Different Variances of Inter-loss Time Observation 1: Non-periodic losses should be considered in adopting WB/RB fairness policies

13. 13 /48 2007/12/12 Fairness Test for TCP Equal-share: Low-multiplexing Traffic RTT-heterogeneity matters for TCP equal-share (b) n = 8 SQRT TFRCP, TFRC, TEAR SIMD IIAD GAIMD Rate-based fairness policy wins Drop-Tail, N=8 n=8 Observation 2: RB fairness policy wins and RTT-heterogeneity matters for TCP equal-share

14. 14 /48 2007/12/12 Aggr. and Resp. Test For TCP Equal-share Normalized Loss Ratio (a) TCP SIMD TEAR IIAD GAIMD TFRC SQRT TFRCP AIAD/H Non- history aggressive policy History/ super-linear aggressive policy Fixed-history responsiveness policy: fewer losses Observation 3: Historical/super-linearly aggressive and fixed-history responsive policies are satisfactory

15. 15 /48 2007/12/12 Summary: Strategies in Eight Schemes TCP-compatibility is not enough Fairness at steady-state and fast agg/resp at transient-state Policy FairnessAggressivenessResponsiveness Aspectthroughput adjusting step/proportion of each inc. curve typelife cycle of loss statistics GAIMDWindow-basedNon-historicalLinearVariable-history IIADWindow-basedHistoricalSub-linearNon-historical SQRTWindow-basedHistoricalSub-linearVariable-history SIMDWindow-basedHistoricalSuper-linearVariable-history AIAD/HWindow-basedHistoricalLinearNon-historical TFRCPRate-basedNon-historicalSuper-linearFixed-history TFRCRate-basedHistoricalLinearFixed-history TEARRate-basedHistoricalLinearFixed-history

16. 16 /48 2007/12/12 Summary: Comparison among Schemes Rate-based fairness policy Historical/super-linear aggressiveness policy Fixed history responsiveness policy Behavior FairnessAggressivenessResponsiveness Criterion TCP-eq (TCP-comp) TCP equal-share TCP-eq (TCP-comp) TCP eq- share TCP-eq (TCP-comp) TCP eq- share Scenario Heavy Losses Non- periodic Losses Low-multiplexing Two-states Losses Bursty Losses Two-states Losses Bursty Losses Homogeneo us RTTs Heterogen eous RTTs GAIMD X (O) Δ(O)XX ΔΔ (Δ)Δ IIAD X (O) ΔX XX (X)X SQRT O (O) X(O)ΔXO (O)Δ O SIMD X (O) Δ(O)XXO (O)OΔ (Δ)X AIAD/H X (O) ΔX XX (X)X TFRCP Δ (O) X(X)ΔOΔ (O)XO (O)O TFRC Δ (O) ΔO ΔO (O)O TEAR X (X) X(O)ΔO XO (O)O O: Satisfactory Δ: Acceptable X: Unacceptable

17. A Fast-Converging TCP-Equivalent Window-Averaging Rate Control Scheme Perform better in terms of fairness, smoothness, aggressiveness, and responsivness

18. 18 /48 2007/12/12 Window-Averaging Rate Control Major rate control:  Real-time estimation (RTE) control model (Rate-based fairness policy) Fairness even under non-periodic losses (variant inter-loss time) Faster aggressiveness Three complemental rate controls:  History-reset (HR) mechanism: (Fixed-history responsiveness policy ) For fast responsiveness  Fluid-based timeout mechanism: For fairness under heavy-losses  One-RTT reduction procedure: For FIFO-managed link

19. 19 /48 2007/12/12 How to Calculate TCP’s Mean Rate? Time TEAR and TFRC: Fixed # of Epoches CWND Epoch, inter-loss time Real-Time Estimation (RTE) Control Model Lower rate under variant inter-loss time WARC adjusts the rate per RTT. WARC averages the latest s CWNDs of a potential TCP flow. CWND Time Fixed # of CWNDs WARC: Fixed # of CWNDs

20. 20 /48 2007/12/12 Fast Aggressiveness 0 -2-3-4 -5 -6 -7-8 TFRC,TEAR WARC

21. 21 /48 2007/12/12 History-reset Mechanism for Fast Responsiveness If then remove CWNDs before the n HR th last loss from rate computing Rate (pkt/RTT) Rounds R(t,s)R(t,s) s rounds T X(-1) X(-2) X(-N) X(-N+1) the last loss T-S(N) the 2 th last loss the 9 th last loss CWND

22. 22 /48 2007/12/12 Analysis of Fairness [Definition] in the steady state a scheme can control a flow to have the same mean rate as TCP does when both perceived the same network conditions Periodic-lossesExpo-lossesStationary-loss WARC === TFRC* =< TCP TFRCP => TCP TEAR =< TCP Scheme Loss conditions

23. 23 /48 2007/12/12 Analysis on Aggressiveness 1/Aggr(m)= the time taken by a scheme to increase its rate with a factor of m. time Last loss rate m 1 ??? 1/Aggressiveness(RTTs) WARC(160) SIMD(1/16) GAIMD(1/5,1/8) TCP IIAD(1,2/3) Fast as the most aggressive scheme [Definition] [JGM03]

24. 24 /48 2007/12/12 Better Tradeoff between Smoothness and Aggressiveness 445 150 1080

25. 25 /48 2007/12/12 Analysis on Responsiveness [Definition] [JGM03] 1/Resp(m) = the number of loss events required by a scheme to decrease the rate with a factor of m.. Smoothness (CV[w]) 1/Responsiveness (#loss events) WARC(160) SIMD(1/16) GAIMD(1/5,1/8) IIAD(1,2/3) WARC more losses for smoothness

26. 26 /48 2007/12/12 Probability of False-Positive Enabling HR Assume X(-j) is an i.i.d. exponential distribution forms a gamma distribution (n, λ) Invoked when the mean of inter-loss time does not change P=10 -3 ->False Positive per 1000 losses 35 mins when W=5~30, RTT=50~300ms [JID04]

27. 27 /48 2007/12/12 Fairness Test for TCP-Equivalence: Under the Variant-Losses Network WARC: Average fixed # of CWND

28. 28 /48 2007/12/12 Fairness Test for TCP Equal-Share 15 Mbps-link 60 Mbps-link Timeout Mechanism Equal share WARC TEAR GAIMD SIMD

29. 29 /48 2007/12/12 Fast Aggressiveness & Responsiveness WARC decreases rate with fewer losses Fast aggressiveness: WARC and SIMD TFRC TEAR WARC w/o One-RTT reduction GAIMD TCP 20sec

30. 30 /48 2007/12/12 Smoothness over Different Time Scale WARC is smooth as TFRC Smoother rate than TCP SIMD GAIMD SQRT IIAD Better smoothness TEAR (0.1 sec)

31. 31 /48 2007/12/12 Low Start-up Latency for Constrained Streaming (e.g. video conference) late packets WARC has low ratio of late packets WARC TCP WARC

32. 32 /48 2007/12/12 Applicability of TCP-equivalent Smooth Rate Controls IP UDP Socket APP RTP/RTCP IP UDP Socket APP RTP/RTCP Rate Control User-layer Solution (IETF Draft) LiveMedia Library (LGPL), DirectShow RTP Filter IP TCP Socket APP Rate Control Kernel-layer Solution (RFC4340, S. Floyd) IP DCCP Socket APP Layered/Base Protocols Supported in Linux Kernel A possible solution in MS Windows Datagram Congestion Control Protocol (DCCP)

33. 33 /48 2007/12/12 Summary WARC  RTE control model + Fixed number of CWNDs Fairness, Aggressivness,  History-reset mechanism Responsiveness TCP-equivalence and TCP equal-share  Fairness under stationary loss condition. For non-periodic loss conditions  Fast Aggr. & Rspo. for drastic change Smoothness

34. Problems on Applying Fair Queuing Discipline to Schedule Requests at Access Gateway for Downlink Differential QoS No-monthly fee solution for downlink differential service

35. 35 /48 2007/12/12 Where to Schedule Packets? Internet GUGU GIGI W1W1 W2W2 G G W3W3 User-side gateway H1H1 HnHn ISP-side gateway access link Uplink requests -> <- Downlink responses User-side gateway (G U ) or ISP-side gateway (G I ) ?  G U is bought by the user’s specification and easy to be managed  G I is owned by ISP. Additional charge may requrie.  Packets are not queued at G U  G I cannot see the IPs of H 1 ~H n Scheduling uplink requests at G U to managing downlink responses Class-based Fair Queuing Queuing packets

36. 36 /48 2007/12/12 monopolizes the link bandwidth sending one-by-one Responses share the downlink neither is appropriate  sending reqs one-by-one  sending a request right after getting a response 1. Time to Release the Next... Packet Request monopolize packets simultaneous responses S S requests

37. 37 /48 2007/12/12 Selecting in the order of service-completion time  Known packet size Fairness should rely on response size Response size is unknown until it returns 2. From Which Queue to Release the Next.. Packet Request S S requests 8 7 4 953 621 Q1 Q2 Q3 packets known packet length ? ? ? ?? ? ??? Q1 Q2 Q3 requests response response size is only available in 1st packet of response

38. 38 /48 2007/12/12 3. User-based Weighted Fairness Class-based  Between different types of traffic: e.g. voice or ftp  Admission Control User-level Differentiation  High-class users get more bandwidth than low- class users

39. 39 /48 2007/12/12 CrCr Q2Q2 QnQn CqCq Requests Response request selector SC 1 SC n W End of RI U W max Minimum-Service First Request Scheduling (MSF-RS) End of Rsp. Minimum-service order arbiter (MOA) Q1Q1 A changes B AB A is referenced by B AB A A is a variable Data flow Window-based rate controller (WRC) request receiver UC 1 UC n request releaser w1w1 w3w3 Minimum-Service First Request Scheduling SC: Service Counter UC: User Counter w: Weight Internet GUGU GIGI H1H1 HnHn

40. 40 /48 2007/12/12 Minimum-service Order Arbiter (MOA) CrCr Q2Q2 QnQn CqCq Requests Response request selector SC 1 SC n W End of RI U W max End of Rsp. Minimum-service order arbiter (MOA) Q1Q1 Window-based rate controller (WRC) request receiver UC 1 UC n request releaser w1w1 wnwn 2. Select from the class with the min SC 1. Log the amount of received service the length of the received response k in bytes

41. 41 /48 2007/12/12 Q2Q2 QnQn CqCq request selector SC 1 SC n Minimum-service order arbiter (MOA) Q1Q1 request receiver UC 1 UC n w1w1 w3w3 Window-based Rate Controller (WRC) Requests Response CrCr W End of RI U W+W+ End of Rsp. Window-based rate controller (WRC) request releaser Release requests if W<W + W : the number of outstanding requests T : the time interval between two updates S i : the responses in bytes received during T C : the link capacity. K: a constant. U i : the link utilization. U + : upper bound of U

42. 42 /48 2007/12/12 Analysis of User-perceived Latency Long queuing time of request+ Short transmission time of response = Short user-perceived latency Client send request Gateway get request Gateway send request Gateway get response Client get response User-perceived latency TqTq TsTs T a =T q +T s Time 0 1 2 (4*1+4*2)/8=1.5 1 1 1 1 2 2 2 2 Example W + =10 W + =20 W + =40 W + =80 T a MSF-RS /T a ordinary

43. 43 /48 2007/12/12 S QiQi QjQj sublink 1 sublink W + Rsp i,1 Rsp i,W + Time Normalized Service Class i Class j t0t0 t1t1 t2t2 0 Analysis for Worst-case Fairness of MSF-RS: D i (t 1,t 2 ): the responses receved by Class i in bytes between t 1 and t 2 w i : the weight of Class i W + : # of sub-links L + : Resp. of max. size Fairness Parameter defined by Golestani for analysis of SCFQ

44. 44 /48 2007/12/12 Weighted Fairness and Sharing Bandwidth Sharing Weighted Fairness Bandwidth per user (Kbps) Class-based User-based Users in Class 1 BW 1 <BW 2 or BW 3

45. 45 /48 2007/12/12 User-Perceived Latency Lower congestion Lower transmission time Client send request Gateway get request Gateway send request Gateway get response Client get response Higher # of concurrent connections Higher loss rate

46. 46 /48 2007/12/12 Experimental Results User-perceived Latency SquidSquid with MSF-RS ms/request1686.11174.9 (includes queuing time 515.5) Throughput 2 Mbps10 Mbps 10 Classes MSF-RS Squid22.428.17 100 Classes MSF-RS Squid23.0129.02 Original Squid31.6142.45 Lower CPU loading due to fewer concurrent transactions in MSF-RS Percentage on CPU utilization

47. 47 /48 2007/12/12 Summary for MSF-RS Scheduling uplink requests -> Control Downlink Responses MSF-RS= Minimum-service Order Arbiter (MOA) + Window-based Rate Control (WRC) User-based weighted fairness Bandwidth Sharing among classes Reduce 20~30% of user-perceived Latency Reduce 25% of CPU loading  Low congestion  Fewer concurrent transactions

48. 48 /48 2007/12/12 Dissertation Conclusions Public Fairness: 1. Taxonomy and evaluation of 8 TCP-friendly schemes TCP-equivalence and TCP equal-share Rate-based fairness + historical/super-linear aggressiveness + fixed history responsiveness TFRC: if meeting TCP-compatibility is the major concern SIMD: if fast aggressiveness is favorable 2. The design of WARC RTE control -> Non-periodic Fairness, Fast aggressiveness as SIMD History-reset procedure -> Fast Responsiveness as TFRC Better Meeting TCP-equivalence and TCP equal-share Smoothness in short-term for interactive constrained streaming Private Fairness: The design of MSF-RS Scheduling Uplink Requests to Manage Downlink Responses User-based Weighted Fairness High utilization while reducing 30% of user-perceived latency Reducing 25% of CPU loading

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