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					          TCP-Carson
A Loss-event Based Adaptive AIMD
   Protocol for Long-lived Flows

          Hariharan Kannan
       Advisor: Prof. M Claypool
       Co-Advisor: Prof. R Kinicki
        Reader: Prof. D Finkel
                   Outline
•   Introduction
•   TCP Behavior
•   TCP-Carson
•   Evaluation
•   Summary
•   Future Work
                         Introduction
• Modern Internet
       •   Short-lived flows e.g. HTTP
       •   Streaming media e.g. Real audio
                                                             Long-lived
       •   Real-time applications e.g. VoIP services
       •   Long-lived flows e.g. FTP
• Heavy tailed
       • 80% bytes are from few connections [Matta, „01]
•   Use TCP
       •   80% of traffic is TCP [Hidenari, „97]
       •   Responsive to congestion – Internet stability
       •   No loss
       •   Router Support to TCP like behavior
       •   More applications are built on top of TCP

 Optimize long-lived flow performance in TCP like fashion
             Modifications to TCP
• TCP – Two phases
   – Slow Start: (till first loss of packet)
        • Aim: Rough estimate of available bandwidth.
        • Congestion Manager [Bala, ‟99], TCP Fast Start [Venkat, „98]

   – Congestion Avoidance:
        • Aim: Optimize window-size, react to network congestion
        • Reno, New-Reno, Vegas, Tahoe
        • AIMD [Yang, „00]: window size = f (increase “a”, decrease “1-b”)
             – Conventional TCP (1, 0.5)
             – Other Equations: a=3b/(2-b) , a=4(1-b²)/3
   – TCP-Carson *
             –   TCP variant, built on top of RENO
             –   Window-based
             –   Fully reliable
             –   Responsive to Congestion

 * Carson City: Located in the State of Nevada, Population: 52457, Founded 1858
                For more details visit http://www.carson-city.nv.us/
The Probing Problem
    drop
       s
               TCP-Carson
• Detects Steady State
  – Losses are periodic
  – Loss interval: Interval in packets between two
    successive losses
• Adapt responsiveness (reaction)
  – Adapt “a”, “b”: (increase, decrease)
• Benefits: Increase throughput, reduce loss,
  reduce window-size variance
                 Outline
• Introduction
• TCP Behavior
  – Congestion Window
  – Loss interval
• TCP-Carson
• Evaluation
• Summary
                        Topology
       s1                                              r1

                              1 Mb, 40ms
       s2         R1                          R2            r2

2 Mb, 10ms        Drop tail                            2 Mb, 10ms
                                           Drop tail
                  Q = 15                                    r3
             s3                            Q = 15
TCP – Cwnd Behavior

    1               16                  1
 Steady           Unsteady           Steady
          - b/w   RTX-TO




                             + b/w
             TCP – Loss interval
 Loss Interval : Number of packets between successive loss events




                    1               16            1


                    Steady       Unsteady        Steady
                  Outline
• Introduction
• TCP Behavior
• TCP-Carson
  – Steady State Detection
    • Metrics
    • Mechanism
  – Algorithm
• Evaluation
• Summary
Steady State Detection - Metrics


          1             1
                16
Steady State Detection - Metrics


         1       16      1
Steady State Detection - Algorithm
• Metric : Weighted Average Loss Interval
  –   Used in TFRC [Floyd, „01]
  –   Evaluated overlapping and distinct windows
  –   Evaluated window sizes from 4 – 32
  –   Chose sliding-32    1 2 3 … … … 31 32 33

  – Equal weights to recent 16
  – Exponentially decreasing weights for prior 16
       • wti = 1, 1 ≤ i ≤ 16
             = 1 - [(i – n/2)/(n/2 +1)] , 17 ≤ i ≤ 32
Steady State Detection - Algorithm
• When Steady?
  – wali(i+1) = wali(i) ± [ 0.1 * wali(i)]
• When Unsteady?
  – wali(i+1) != wali(i) ± [ 0.1 * wali(i)]
  – Retransmission timeout
  – No loss for long time
• See how it works!!!
Steady State – 10 Flows
Steady State – Varying # of flows
       4       8    16       8       4




   4       8       16    8       4
      TCP–Carson : Algorithm
                     “a”          “b”

• AIMD Table:       0.148        0.875
                    0.250        0.750
                    0.750        0.600
                    1.000        0.500         TCP
                                           (start here)
• detect_state(loss_interval)
• if (steady) { go_up() }
• if (unsteady) {go_down()} //become TCP

• Okay dude!!! Show me the results!!!!
                   Evaluation
•   1 TCP-Carson
•   1 TCP-Carson, 1 CBR
•   1 TCP-Carson, 1 TCP-Reno
•   4 TCP-Carson, 4 TCP-Reno
•   7 TCP-Carson, 1 TCP-Reno
•   1 TCP-Carson, 7 TCP-Reno
•   8 TCP-Carson
•   20 TCP-Carson
•   Varying flow life-times – Varying number of flows
1TCP-Carson
   1 TCP-Carson, 1 CBR(0.5Mb)

1 Carson, 1 UDP              1 Carson, 1 UDP




                  1 Carson
1TCP-Carson, 1TCP-Reno
4-Carson, 4-Reno
8 TCP-Carson flows
                                      Evaluation
                 Single Flow                          1-Carson, 1-Reno
                  Carson       Reno                       Carson   Reno
    Avg Cwnd       27.7        24.4         Avg Cwnd      14.6      12.6
    Loss           121         167          Loss          124       180
    Thruput        0.948       0.944        Thruput       0.511     0.437



              4-Carson, 4-Reno                        8-Carson / 8-Reno
                  Carson       Reno                       Carson   Reno
    Avg Cwnd       8.7         7.7          Avg Cwnd      8.1       7.0
    Loss           158         172          Loss          90        134
    Thruput *      0.187       0.161        Thruput       0.121     0.109

    * Note: Bottleneck bandwidth was 1.5M


•    TCP friendly in all cases
•    Average throughput less than TCP response function for (loss, RTT) combination
                 Summary
•   TCP variant (on top of Reno)
•   Detects Steady State
•   Adapts responsiveness
•   Benefits:
    – Increase throughput
    – Reduces loss
    – Reduce window-size variance
    – End-to-End protocol
               Future Work
•   AIMD action
•   RED/ECN effect
•   Application performance
•   Slow-start, high congestion periods
•   Steady state detection algorithms
          TCP-Carson
A Loss-event Based Adaptive AIMD
   Protocol for Long-lived Flows

          Hariharan Kannan
       Advisor: Prof. M Claypool
       Co-Advisor: Prof. R Kinicki
        Reader: Prof. D Finkel

				
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posted:12/21/2011
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