Download - Modeling of Web/TCP Transfer Latency
Modeling of Web/TCP Transfer LatencyYujian Peter Li January 22, 2004
M. Sc. Committee: Dr. Carey WilliamsonDr. Wayne EberlyDr. Elena Braverman
Department of Computer Science, University of Calgary
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Outline
TCP Overview and Related Work
The Proposed TCP Transfer Latency Model
Model Validation by Simulation
Extending the Proposed Model to CATNIP TCP
Conclusions
Motivation and Objectives
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Motivation
Web response time Highly dominated by TCP performance
Understanding the sensitivity of TCP to network conditions helps to improve TCP performance
No work on modeling CATNIP TCP
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Objectives
To survey and compare existing TCP models
To develop an accurate model for short-lived TCP flows
To model CATNIP TCP
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SYNSYN/ACK
ACK
FIN FIN/ACKACK
TCP OverviewCharacteristics
Reliable, in-order byte stream
Flow control Connection-oriented Congestion Control
Web Browser Web Server DATA
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TCP OverviewCongestion Control
• When intermediate nodes (routers) become overloaded, the condition is called congestion.
• The mechanisms to solve the problem are called congestion control.
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TCP Overview – Congestion ControlSlow Start & Congestion Avoidance
Slow start: cwnd=cwnd+1 for every received ACK
Congestion avoidance: cwnd = cwnd + 1/cwnd
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Related Work
TCP Steady State Throughput Model [Padhye et al. 1998]
TCP Response Time Models Cardwell-00 Model [Cardwell et al. 2000] Padhye Model [Cardwell et al. 1998] Cardwell-98 Model [Cardwell et al. 1998] Sikdar Model [Sikdar et al. 2001]
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The Proposed TCP Response Time ModelAssumptions
Bernoulli packet loss model, i.e., packet is independently lost with fixed probability p Congestion avoidance algorithm ignored, i.e., cwnd always increases by one upon receiving one ACK (exponentially)
Packet loss can be via RTO or triple duplicate ACKs
The effect of delayed ACK, Tdelay, is added when necessary
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The Proposed Model (Cont’d)Congestion Window Evolution
iloss
iss
lastCycle
iTTET
][
1
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Simulation ExperimentsNetwork Topology
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Factor Levels
Transfer Size 1KB, 4KB, 8KB, 16KB, 32KB, 50KB, 64KB, 90KB, 110KB, 128KB, 160KB, 180KB, 200KB
Packet Loss Probability 1%, 3%, 5%, 8%, 10%
Simulation ExperimentsMetric & Experimental Factors
Performance Metric: Data Transfer Time, the time from when the sender sends the first packet until the time when the sender receives the ACK of the last data packet.
Experimental factors and levels
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Simulation ResultsShort-lived Flows
( p=3%) (p=10%)
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0 5 10 15 20 25 30 35 40
Data Transfer Size (Packets)
Tran
sfer
Tim
e (s
ec)
Simulated
Proposed
Sikdar
Cardwell-000
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0 5 10 15 20 25 30 35 40
Data Transfer Size (Packets)
Tran
sfer
Tim
e (s
ec)
Simulated
Proposed
Sikdar
Cardwell-00
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CATNIP TCP
C. Williamson and Q. Wu : “A Case for Context-Aware TCP/IP”.
ACM Performance Evaluation Review, Vol. 29, No. 4, pp. 11-23, March 2002. Convey application-layer context information to TCP/IP Not all packet losses created equal
IP
TCP
HTTPDocument Size
Packet Loss Priority
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CATNIP TCP v.s. Partial CATNIP TCP
Packets First three
Last three
cwnd<3
CATNIP
Partial CATNIP
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0
10
20
30
40
50
60
70
1 2 3 4 5 6 7 8 9 10
Transfer Time (sec)
Fre
qu
ency
(%
)
Partial CATNIP
CATNIP
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0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 1 2 3 4 5 6 7 8
Transfer Time (sec)
Cu
mu
lati
ve F
ract
ion
Partial CATNIP
CATNIP
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10
20
30
40
50
60
70
1 2 3 4 5 6 7 8 9 10
Transfer Time (sec)
Fre
qu
ency
(%
)
Partial CATNIP
CATNIP
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0.1
0.2
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0.5
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0.7
0.8
0.9
1
0 1 2 3 4 5 6 7 8
Transfer Time (sec)
Cu
mu
lati
ve F
ract
ion
Partial CATNIP
CATNIP
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10
20
30
40
50
60
70
1 2 3 4 5 6 7 8 9 10
Transfer Time (sec)
Fre
qu
ency
(%
)
Partial CATNIP
CATNIP
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0.1
0.2
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0.4
0.5
0.6
0.7
0.8
0.9
1
0 1 2 3 4 5 6 7 8
Transfer Time (sec)
Cu
mu
lati
ve F
ract
ion
Partial CATNIP
CATNIP
CATNIP TCP v.s. Partial CATNIP TCP
p=3%
p=5%
p=10%
PDF CDF
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Modeling Partial CATNIP TCP Short-lived Flows
( p=3% p’=0%) (p=10% p’=0%)
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0 5 10 15 20 25 30 35 40
Data Transfer Size (Packets)
Tran
sfer
Tim
e (s
ec)
TCP Reno (Simulated)
Partial CATNIP (Simulated)
Partial CATNIP (Analytical)
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0 5 10 15 20 25 30 35 40
Data Transfer Size (Packets)
Tran
sfer
Tim
e (s
ec)
TCP Reno (Simulated)
Partial CATNIP (Simulated)
Partial CATNIP (Analytical)
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Conclusions
The proposed TCP latency model fits the simulation results better than earlier models.
The differences between Partial CATNIP and CATNIP are minimal when p<10%.
Partial CATNIP TCP model matches the simulation as well.
Partial CATNIP TCP improves TCP latency compared to TCP Reno. For short-lived flows, Partial CATNIP TCP is about 10% faster than TCP Reno in most cases.
CATNIP TCP is a suitable approach to improve TCP Performance.