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TCP Westwood. The work is supported by the 2/032/2004 ELTE-BUTE-Ericsson NKFP project on  Research and Developments of Tools Supporting Optimal Usage of Heterogen  Communication Networks. The Role of PCE in the Evolution of Transport Protocols. Pfldnet 2005, Lyon, France - PowerPoint PPT Presentation

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  • TCP WestwoodThe work is supported by the 2/032/2004 ELTE-BUTE-Ericsson NKFP project on Research and Developments of Tools Supporting Optimal Usage of Heterogen Communication Networks

  • The Role of PCE in the Evolution of Transport Protocols Pfldnet 2005, Lyon, France

    M. Y. Medy Sanadidi

    http://www.cs.ucla.edu/~medyhttp://www.cs.ucla.edu/NRL/hpi/tcpw/

  • Recent Issues in Transport ProtocolsLarge Pipes UtilizationSteady stateStart-upImpact of Wireless Links:Last-hop wirelessMultihop contention networksFairness for asymmetric flows Protocols Co-ExistenceNew Paradigms:Voice/VideoStore-and-forward at Transport layer (e.g. PEPs, P2P/Overlays)

  • Example: Satellite/802.11 Networks

  • Outline Path Characteristics Estimation (PCE)Prospects for Higher EfficiencyFuture of Friendly Co-Existence Addressing the New ParadigmsSummary

  • Path Characteristics Estimation (PCE)Characteristics of Interest:Links capacityPath dynamic range, i.e. buffering capacityCross traffic level, path-persistence, responsivenessRandom lossMultihop wireless connectivity, contention, route diversityParticipating Nodes:Sources onlySources and DestinationsForwarding nodes (routers, base stations, multihop wireless nodes)

  • Sharing a LinkFlow2Flow12 flows, red one is non-responsivefair share ?bandwidthresidual bandwidthbottleneckinterface queuebacklogBuffer spacePropagation Time

  • A Hierarchy of CharacteristicsAchieved rateDelay/Dynamic RangePacket lossIntensityPath persistenceElasticityLinks capacitiesPropagation timesBuffer spaceErrorsCross Traffic LoadArchitectureFlow Behavior+

  • Path Capacity EstimationPath Capacity: capacity of narrow linkPathrate: rely on packet pair dispersion measurements followed by statistical processing of resultsCapProbe: use dispersion measurements; perform on line filtering of results based on end-to-end delayTcpProbe: an adaptation of CapProbe into TCP with minimal sender side only changes

  • CapProbe and TcpProbe

  • Prospects for Higher EfficiencySteady State:Congestion avoidance (FAST): stable at high throughput, co-existence ??, and random loss impact ??Scaling up congestion recovery (HSTCP, STCP): higher throughput, but fairness and stability ??Scaling up congestion recovery (BIC): improves on the above in fairnessForwarder Based (XCP): superb, when we are done with implementation issuesPCE reliance (TCP Westwood, TCP Peach): Peach requires forwarder priority support, TCPW requires good estimation at high speeds

  • Using PCETahoe/Reno/NewReno estimate:Packet loss via Dup AcksRTT average and varianceMaintain a pipe size (or bandwidth-delay product) estimate: ssthreshVegas/FAST:Achieved Rate and its relation to the Expected Rate, or equivalently RTT and RTTmin, or Queuing delayHSTCP/STCP/BIC:Use current window size (Expected Rate) in addition to all items above in Reno

  • Using PCE (2)TCPW estimatesPacket loss and type of lossNarrow link capacity, or Path capacityAchieved RateDynamic Range resulting from buffering space:(RTTmax-RTTmin)XCP measures at forwarders the actual:Links capacitiesLoad intensityRTT (obtained from sources)

  • Large Pipes Measurements Results

  • Experiments Environment

    (Powerful Machines)CPU: Xeon 3.06GHzCache: 512 L2/ 1MB L3Intel 1000PROPCI-X BUS 133MHz

    NewReno Sender

    Advanced TCPSender

    Gigabit link

    UCLAGigabit Switch

    Gigabit link

    NewReno Receiver(Alabama)

    Internet2

    NewReno Receiver(Caltech)

    PATHNETS 2004 - San Jose CA

  • Acceptable Long Term Efficiency

  • UCLA-Alabama

    PATHNETS 2004 - San Jose CA

  • Some Difference in Completion Times

  • Transfer Completion Times

    On average:

    TCPW and FAST: 0 to 100 MB in 5.8 Sec! HSTCP: 0 to 100 MB in 7.5 Sec!NewReno: 0 to 100 MB in 11 Sec!

    UCLA-Alabama

    PATHNETS 2004 - San Jose CA

  • Co-Existence at Gbps Speed

  • Friendliness

    UCLA-CalTech

    PATHNETS 2004 - San Jose CA

  • Random Loss Impact

  • Random Loss Emulation

    Induced non-congestion packet loss in emulator (PER 0.1% up to 0.5%)TCPW throughput much higher than all other schemes

    AdvancedTCPSender

    NewReno Receiver(Alabama)

    UCLA Alabama

    UCLA-Alabama

    NistnetNetwork Emulator

    PATHNETS 2004 - San Jose CA

  • Effect of Random Loss

  • Random Loss Emulation (Results)

    UCLA-Alabama

    PATHNETS 2004 - San Jose CA

    Chart1

    49.4330.254.71

    22.8312.143.03

    12.928.62.26

    TCPW

    FAST

    HSTCP

    Average Throughput (Mbps)

    Sheet1

    FASTWWHSTCPNewReno

    (0-1)1.471.216.044.63

    (1-2)13.712.910.57.58FASTTCPWHSTCPNewReno

    15.1714.1116.5412.21015.1714.1116.5412.21

    (2-3)14.814.810.67.74129.9728.9127.1419.95

    29.9728.9127.1419.95244.7743.6137.8427.93

    (3-4)14.814.710.77.98359.5758.1148.7435.81

    44.7743.6137.8427.93474.3772.2159.9444.02

    (4-5)14.814.510.97.88589.1787.0171.1452.22

    59.5758.1148.7435.816103.97101.7182.5460.53

    (5-6)14.814.111.28.217118.77116.1193.9469.09

    74.3772.2159.9444.028133.07130.61105.5477.76

    (6-7)14.814.811.28.2986.63

    89.1787.0171.1452.221095.55

    (8-9)14.814.711.48.3111104.54

    103.97101.7182.5460.53

    (9-10)14.814.411.48.56

    118.77116.1193.9469.09

    (10-11)14.314.511.68.67

    133.07130.61105.5477.76

    8.87

    86.63

    8.92

    95.55

    8.99

    104.54

    Sheet1

    0000

    0000

    0000

    0000

    0000

    0000

    0000

    0000

    0000

    0000

    0000

    0000

    FAST

    TCPW

    HSTCP

    NewReno

    Sheet2

    49.4310.1522.832.6812.921.09

    30.256.6712.145.858.60.45

    4.710.673.030.332.260.2

    0.10%0.25%0.50%

    TCPW49.4322.8312.92

    FAST30.2512.148.6

    HSTCP4.713.032.26

    Sheet2

    000

    000

    000

    TCPW

    FAST

    HSTCP

    Average Throughput (Mbps)

    Sheet3

  • TCPW: Mining ACK Streams for PCERely on PCE ( e.g. capacity, achieved rate, dynamic range) to determine an Eligible Rate Estimate (ERE)ERE is used to size the congestion window after a packet lossReceiverSenderInternetBottleneckpacketsACKsmeasure

  • TCPW BE (2001)BE Sampling:~ Packet pair a noisy estimate of achieved rate/capacity Provides throughput boost under random loss, overestimates under congestionEfficient but not friendly

    Congestion occurs whenerver the low-frequency input traffic rate exceed the link capacity

  • BE: filtering the ACK reception ratebk = SkDiscretizing a continuous low-pass filter (Tustin-approximation)1/ : cut-off frequencytk = tk tk-1

    Interarrival time increases ! bk-1 has less significance, it represents an older value

  • TCPW RE (2002)RE Sampling:~ Packet trainFair estimate under congestion, underestimates under random lossUsed in TCPW RE and in TCP Westwood+ R. Ferorelli, L. A. Grieco, S. Mascolo, G. Piscitelli, P. Camarda, Live Internet Measurements using Westwood+ TCP Congestion Control, IEEE Globecom 2002 (Taipei, Taiwan, November 18-20, 2002).Friendly

  • REBusty TCP traffic ! BE may over-estimate the fair share

    Value in the near past has the same influence as a more current measurement

  • Adaptive Estimation in TCPW

    TCPW CRB: ERE BE if random loss, else ERE RE

    TCPW ABSE: ERE RE

  • TCPW CRB (2002)ERE BE if random loss, else ERE RE

    Combined Rate and BandwidthBinary adaptiveCongestion measure: Expected Rate/Achieved RateClarified Efficiency/Friendliness tradeoffCongestion measurePacket Loss Detectedssthresh, cwnd = BE x RTTminover a threshold under a threshold Ssthresh, cwnd = RE x RTTmin

  • CRB method (2/1)Identifying predominant cause of packet losscwnd >> RE * RTTmin (estimated pipe size) ) loss due to congestion

    Congestion caseLink-error caseCongestion measure:cwnd / ((RE * RTTmin )) / seg_size)

  • CRB method (2/2)= 1.8

  • TCPW ABSE (2002)Under CongestionUnder No Congestion Adaptive Bandwidth Share EstimationAdapt the sample interval Tk according to congestion level Congestion measure, similar to VegasTk ranges from one interACK interval to current RTTBetter Efficiency/Friendliness profile than CRB[WVSG02] Ren Wang, Massimo Valla, M. Y. Sanadidi, and Mario Gerla, "Adaptive Bandwidth Share Estimation in TCP Westwood", In Proc. IEEE Globecom 2002, Taipei, Taiwan, R.O.C., November 17-21, 2002

  • ABSE: Adaptive sampling interval (Tk)Longer T ) RE more conservativeMore severe congestion ) longer T should be

  • ABSE: Filter Gain Adaptation (k) 2/1

  • ABSE: Filter Gain Adaptation (k) 2/2

    Network Instability: [KN01] Umax : max Ui in the last N obervations(=0.6, N=10)

  • Helping Short Lived ConnectionsApproaches:Cached ssthreshLarger initial windowPCE based: Hoes; TCPW AstartNegotiation: Quick-StartNo problems here for XCP!

  • TCPW Astart (2003)Take advantage of ERE :Adaptively and repeatedly reset ssthresh ERE until sender window reaches estimated pipe size, or encounters packet lossIncludes multiple mini exponential increase, and mini linear increase phasescwnd grows slower as it approaches BDPConnection converges faster to its pipe size with less buffer overflow, since it adapts to pipe size and transient loading

  • Astart: friendliness

  • Astart: First 20 Seconds ThroughputRTT =100ms, Buffer =BDPRTT =100ms, Bottleneck =40 MbpsBottleneck capacity = 40 Mbps, Buffer =BDP

    Good scaling with capacity and propagation timeRobust to buffer size variation

  • Agile Probing (=Astart)