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TCP Westwood

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

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TCP Westwood

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  1. 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

  2. The Role of PCE in the Evolution of Transport Protocols Pfldnet 2005, Lyon, France M. Y. “Medy” Sanadidi http://www.cs.ucla.edu/~medy http://www.cs.ucla.edu/NRL/hpi/tcpw/

  3. Using PCE • Tahoe/Reno/NewReno estimate: • Packet loss via Dup Acks • RTT average and variance • Maintain a pipe size (or bandwidth-delay product) estimate: ssthresh • Vegas/FAST: • Achieved Rate and its relation to the Expected Rate, or equivalently RTT and RTTmin, or Queuing delay • HSTCP/STCP/BIC: • Use current window size (Expected Rate) in addition to all items above in Reno

  4. Using PCE (2) • TCPW estimates • Packet loss and type of loss • Narrow link capacity, or Path capacity • Achieved Rate • “Dynamic Range” resulting from buffering space: (RTTmax-RTTmin) • XCP measures at forwarders the actual: • Links capacities • Load intensity • RTT (obtained from sources)

  5. Effect of Random Loss

  6. TCPW: Mining ACK Streams for PCE • Rely 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 loss Bottleneck packets Receiver Sender ACKs Internet measure

  7. Tk TCPW BE (2001) BE Sampling: • ~ Packet pair • a noisy estimate of achieved rate/capacity • Provides throughput boost under random loss, overestimates under congestion • Efficient but not friendly • Congestion occurs whenerver the low-frequency input traffic rate exceed the link capacity

  8. BE: filtering the ACK reception rate • bk = Sk • Discretizing a continuous low-pass filter(Tustin-approximation) • 1/ : cut-off frequency • tk = tk – tk-1 • Interarrival time increases ! bk-1 has less significance, it represents an older value

  9. Tk TCPW RE (2002) • RE Sampling: • ~ Packet train • Fair estimate under congestion, underestimates under random loss • Used 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

  10. RE • Busty TCP traffic ! BE may over-estimate the fair share • Value in the near past has the same influence as a more current measurement

  11. Adaptive Estimation in TCPW TCPW CRB: ERE  BE if random loss, else ERE RE TCPW ABSE: ERE  RE<X <BE by continuously adapting the bandwidth sample width to congestion level TCPW Astart: use ERE to help short lived flows[WPYSG04] Ren Wang, Giovanni Pau, Kenshin Yamada, M. Y. Sanadidi, Mario Gerla " TCP Startup Performance in Large Bandwidth Delay Networks ", INFOCOM 2004, Hong Kong, March 2004 TCPW BBE: ERE  u * C + (1-u) * RE, where uis a congestion measure taking into account path dynamic range

  12. Binary adaptation TCPW CRB (2002) ERE  BE if random loss, else ERE RE • Combined “Rate” and “Bandwidth” • Binary adaptive • Congestion measure: Expected Rate/Achieved Rate • Clarified Efficiency/Friendliness tradeoff over a threshold  ssthresh, cwnd = BE x RTTmin Packet Loss Detected Congestionmeasure Ssthresh, cwnd = RE x RTTmin under a threshold 

  13. CRB method (2/1) • Identifying predominant cause of packet loss • cwnd >> RE * RTTmin (estimated pipe size) ) loss due to congestion Link-error case Congestion case • Congestion measure: cwnd / ((RE * RTTmin )) / seg_size)

  14. CRB method (2/2) = 1.8

  15. Tk Tk TCPW ABSE (2002) Under No Congestion Under Congestion • Adaptive Bandwidth Share Estimation • Adapt the sample intervalTk according to congestion level • Congestion measure, similar to Vegas • Tk ranges from one ‘interACK’ interval to current RTT • Better 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

  16. Bw share sample: • > cwnd ) no congestion, Tk = Tmin (ACK interarrival time) otherwise • RE: ABSE: Adaptive sampling interval (Tk) • Longer T ) RE more conservative • More severe congestion ) longer T should be

  17. ABSE: Filter Gain Adaptation (k) 2/1

  18. ABSE: Filter Gain Adaptation (k) 2/2 • Network Instability: [KN01] • Umax : max Ui in the last N obervations (=0.6, N=10)

  19. Helping Short Lived Connections • Approaches: • Cached ssthresh • Larger initial window • PCE based: Hoe’s; TCPW Astart • Negotiation: Quick-Start • No problems here for XCP!

  20. 510 cwnd 500 Linear increase phases 490 480 470 cwnd in packets 460 450 440 Exponential increase phases 430 420 1.6 1.7 1.8 1.9 2 2.1 2.2 Time (sec) TCPW Astart (2003) • Take advantage of ERE : Adaptively and repeatedly reset ssthresh ERE until sender window reaches estimated pipe size, or encounters packet loss • Includes multiple mini ‘exponential increase’, and mini ‘linear increase’ phases • cwnd grows slower as it approaches BDP • Connection converges faster to its pipe size with less buffer overflow, since it adapts to pipe size and transient loading

  21. Astart: friendliness

  22. [YWSG04] Kenshin Yamada, Ren Wang, and M.Y. Sanadidi and Mario Gerla " TCP Westwood with agile probing: Dealing with dynamic, large, leaky pipes ", In Processing of IEEE ICC. volume 2. pages 1070-1074. 2004 [WYSG05] Ren Wang, Kenshin Yamada, M. Yahya Sanadidi, and Mario Gerla " TCP with sender-side intelligence to handle dynamic, large, leaky pipes ", IEEE Journal on Selected Areas in Communications, 23(2):235-248, 2005. Agile Probing (=Astart) & Persistent Non-Congestion Detection (PNCD) • Demo:

  23. PNCD • Similar to the idea of CBR • ER: expected rate ≈ cwnd/RTTmin(in non-congestion) • RE: Achived Rate corresponding to ER 1.5 RTT earlier • IER: Initial ER ssthresh/RTTmin • CongestionBoundary =  ER + (1-) IER

  24. TCPW BBE (Work in Progress) • With H. Shimonishi (NEC, Tokyo) • “Buffer” and “Bandwidth” Estimation • Estimates Capacity using TcpProbe (much more accurate than BE!!) • Higher efficiency at higher random loss rates (e.g. 5-10%) • Estimates Dynamic Range (related to buffer size) • Improves TCPW control as a function of congestion • The result is higher efficiency and robust friendliness even at small buffers! WN29-3 Improving Efficiency-Friendliness Tradeoffs of TCP in Wired-Wireless Combined Networks Hideyuki Shimonishi, NEC, Medy Sanadidi, Mario Gerla, University of California at Los Angeles, ICC 2005, 15 May - 19 May 2005 ? ?

  25. Relative Frequency RTTcong_loss RTTmin Congestion loss Random loss RTT beforepacket loss TCPW BBE Algorithms (ICC 2005) Dynamic Range estimate Dmax = RTTcong loss - RTTmin Current Delay Distance D = RTT– RTTmin Eligible Rate estimate ERE = u * C + (1-u) * RE Note: u=0 if D and Dmax are small

  26. The Role of PCE in the Evolution of Transport Protocols Pfldnet 2005, Lyon, France M. Y. “Medy” Sanadidi http://www.cs.ucla.edu/~medy http://www.cs.ucla.edu/NRL/hpi/tcpw/

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