TCP-CarsonA 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• 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

Long-lived

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 Problemdrop

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

R2R1

r1

r2

r3s3

s2

s1

1 Mb, 40ms

2 Mb, 10ms 2 Mb, 10msDrop tail

Q = 15

Drop tail

Q = 15

TCP – Cwnd Behavior

1 16 1

Steady Unsteady SteadyRTX-TO- b/w

+ b/w

TCP – Loss interval Loss Interval : Number of packets between successive loss events

1 16 1

Steady SteadyUnsteady

Outline

• Introduction• TCP Behavior• TCP-Carson

– Steady State Detection• Metrics• Mechanism

– Algorithm

• Evaluation• Summary

Steady State Detection - Metrics

1 116

Steady State Detection - Metrics

1 116

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

– 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

1 2 3 … … … 31 32 33

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

4 8 16 8 4

Steady State – Varying # of flows

4 8 16 8 4

TCP–Carson : Algorithm

• AIMD Table:

• detect_state(loss_interval) • if (steady) { go_up() }• if (unsteady) {go_down()} //become TCP

• Okay dude!!! Show me the results!!!!

“a” “b”

0.148 0.875

0.250 0.750

0.750 0.600

1.000 0.500 TCP

(start here)

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

  Carson Reno

Avg Cwnd  27.7  24.4

Loss  121  167

Thruput  0.948  0.944

Single Flow

  Carson Reno

Avg Cwnd  14.6  12.6

Loss 124 180

Thruput  0.511  0.437

1-Carson, 1-Reno

  Carson Reno

Avg Cwnd  8.7  7.7

Loss  158 172

Thruput *  0.187 0.161

4-Carson, 4-Reno

  Carson Reno

Avg Cwnd 8.1  7.0

Loss  90  134

Thruput  0.121  0.109

8-Carson / 8-Reno

* 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-CarsonA 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