Receiver Driven Bandwidth Sharing for TCP

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Receiver Driven Bandwidth Sharing for TCP

• Authors Puneet Mehra, Avideh Zakor and
  Christophe De Vlesschouwer
• University of California Berkeley.
• Presented at INFOCOM 2003. Twenty-Second Annual
  Joint Conference of the IEEE Computer and
  Communications Societies.

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Overview of the Presentation

• Motivation
• Goals
• Proposed Method
• NS-2 Simulations
• Conclusion

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Motivation

• Most Internet traffic is TCP
• HTTP, FTP, P2P, Multimedia streaming
• In many cases access links are bottleneck
• Limited Bandwidth (B/W) eg DSL/Cable lt 1.5Mbps
• User run many apps that compete for B/W
• Problem TCP shares bottleneck B/W according to
  RTT
• Not fair to flows with large RTT
• Doesnt consider application needs or user prefs!

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Example
FTP
Low RTT
INTERNET
P2P
Video traffic
Med. RTT
High RTT
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Goals

• Achieve full utilization of the receivers access
  link (bottleneck).
• Satisfy user preferences
• -priorities assigned to each flow.
• Approach limit throughput of low-priority flows
  to provide additional B/W for high-priority ones

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Overview of the Presentation

• Motivation
• Goals
• Proposed Method
• NS-2 Simulations
• Conclusion

7
System Overview
User Preferences
W1 d1
R1
T1
TRAS Target Rate Allocation Sub-System
FCS1 Flow Control System
Sender1
. . .
. . .
Internet
Wn dn
s
Tn
FCSn Flow Control System
s Calculation Sub-System
Rn
R1
Sendern
Rn
For the receiver s system target bit-rate For
the nth connection Wn Advertised Window dn
Delay in ACK packets Tn Target Rate Rn
Measured Rate
BWSSBandwidth Sharing System
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System Overview

• Band-Width Sharing System (BWSS) consists of
• a) Flow Control System (FCS)
• b) Target Rate Allocation Sub-system (TRAS)
• c) s Calculation Sub-system.

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Flow Control System
For the nth connection W Advertised
Window d Delay in ACK packets
R Measured Rate P Packet size in
bits Ti Target Rate mi
minimum bandwidth wi weight
Measure Bit-rate and RTT
R1
Adapt Receiver Window / ACK Delay
Calculate Target Rate Measured Rate
W1
T1
d1
FCS1 Flow Control System
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Flow Control System

• Ri lt Ti search for the smallest Wi to achieve
  (1- a )Ti lt Ri lt (1 a )Ti
• If Ri gt (1a)Ti then delay the ACKs as
  decreasing Wi is ineffective.
• Aim to minimize delay otherwise results in
  unresponsiveness instability in TCP flow.

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Example
After fast recovery
Receivers advertised window
Window size limits the data rate Max Window
size min (cwndmax, receivers adv. window)
Slide borrowed from Dr. Nitin Vaidyas TCP
tutorial
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RTT and Bandwidth estimation

• TCP timestamp option to estimate RTT.
• Bandwidth estimation relies on exponentially
  weighted moving average
• R ? aR (1-a)Rø
• Ø bandwidth estimation period, tradeoff between
  accuracy of estimation and time for convergence.

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Target Rate Allocation System
T1

• Some apps need minimum guaranteed rate(video),
  others dont (ftp)
• User assigns each flow
• Priority (pi), minimum rate (mi) and weight (wi)
• Bandwidth allocation algorithm
• Satisfy minimum rate in decreasing order of
  priority
• Remaining B/W shared according to weight

Prevents starvation of low priority connection
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s Calculation Subsystem
R1
s
U Si Ri
RN
Goal Choose s to maximize link utilization. U
Si Ri (s) Approach Iteratively increase/decrease
s and measure the impact on utilization
s lt sideal implies under-utilization of the
link. If s gt sideal , does it affect the system ?
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Overview of the Presentation

• Motivation
• Goals
• Proposed Method
• NS-2 Simulations
• Conclusion

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Example of User Preferences
Time 0 Min. Rate 0 Kb/s weights 1,2,3 for
S0-S2 Priority -gt S0 (max), S2(min) Time 300
Min Rate 600 Kb/s
TCP
BWSS
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Network-Congestion Example
Priorities increasing from S0-S2 Min Rate S0,S2
600Kb/s S1 100 Kb/s Time 400s to
1200s 700Kb/s Interfering TCP traffic S2 limited
to 300Kb/s
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Multimedia Streaming Example

• S0 Ftp traffic. Low Priority
• Min Rate 700Kb/s
• S1 Streaming at 450Kb/s
• High Priority
• 300Kb/s UDP flow (400s-1000s)

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Overview of the Presentation

• Motivation
• Goals
• Proposed Method
• NS-2 Simulations
• Conclusion

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Conclusion

• BWSS allows user to allocate link B/W
• Flexible B/W allocation model
• Adapts to changing network conditions
• No changes to TCP/senders/routers
• Observation
• - works only if desired rate is achievable
  under flows cwnd
• - What was receiver window advertisement
  actually designed for??

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Observation TCP window management
sender
receiver
1
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Questions??