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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. Overview of the Presentation.

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Receiver driven bandwidth sharing for tcp l.jpg

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.


Overview of the presentation l.jpg

Overview of the Presentation

  • Motivation

  • Goals

  • Proposed Method

  • NS-2 Simulations

  • Conclusion


Motivation l.jpg

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 < 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

    • Doesn’t consider application needs or user prefs!


Example l.jpg

Congestion

Example:

FTP

Low RTT

INTERNET

P2P

Video traffic

Med. RTT

High RTT


Goals l.jpg

Goals

  • Achieve full utilization of the receiver’s 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


Overview of the presentation6 l.jpg

Overview of the Presentation

  • Motivation

  • Goals

  • Proposed Method

  • NS-2 Simulations

  • Conclusion


System overview l.jpg

System Overview

User

Preferences

W1 & d1

R1

T1

TRAS

Target Rate Allocation Sub-System

FCS1

Flow Control System

Sender1

.

.

.

.

.

.

Internet

Wn & dn

σ

Tn

FCSn

Flow Control System

σ

Calculation

Sub-System

Rn

R1

Sendern

Rn

For the receiverσ= system target bit-rate

For the nth connectionWn= Advertised Windowdn = Delay in ACK packetsTn= Target RateRn = Measured Rate

BWSSBandwidth Sharing System


System overview8 l.jpg

System Overview…

  • Band-Width Sharing System (BWSS) consists of:

    a) Flow Control System (FCS)

    b) Target Rate Allocation Sub-system (TRAS)

    c) σ Calculation Sub-system.


Flow control system l.jpg

Flow Control System

For the nth connectionW = Advertised Windowd = Delay in ACK packetsR = Measured RateP = Packet size in bitsTi= Target Ratemi = minimum bandwidthwi= weight

Measure

Bit-rate and RTT

R1

Adapt

Receiver Window / ACK Delay

Calculate

Target Rate – Measured Rate

W1

T1

d1

FCS1

Flow Control System


Flow control system10 l.jpg

Flow Control System…

Ri < Ti : search for the smallest Wi to achieve (1- α )Ti =< Ri =< (1+ α )Ti

If Ri > (1+α)*Ti then delay the ACKs as decreasing Wi is ineffective.

Aim to minimize delay : otherwise results in unresponsiveness & instability in TCP flow.


Example11 l.jpg

Example

After fast recovery

Receiver’s advertised window

Window size limits the data rate :

Max Window size = min (cwndmax, receiver’s adv. window)

Slide borrowed from Dr. Nitin Vaidya’s TCP tutorial


Rtt and bandwidth estimation l.jpg

RTT and Bandwidth estimation

  • TCP timestamp option to estimate RTT.

  • Bandwidth estimation relies on exponentially weighted moving average

    R  α*R + (1-α)*Rø

  • Ø – bandwidth estimation period, tradeoff between accuracy of estimation and time for convergence.


Target rate allocation system l.jpg

σ

User Prefs.

Tn

Target Rate Allocation System

T1

  • Some apps need minimum guaranteed rate(video), others don’t (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


Calculation subsystem l.jpg

σ – Calculation Subsystem

R1

σ

U = Σi Ri

RN

Goal: Choose σ to maximize link utilization. U = Σi Ri (σ)

Approach: Iteratively increase/decrease σ and measure the impact on utilization

σ < σideal implies under-utilization of the link.

If σ > σideal , does it affect the system ?


Overview of the presentation15 l.jpg

Overview of the Presentation

  • Motivation

  • Goals

  • Proposed Method

  • NS-2 Simulations

  • Conclusion


Slide16 l.jpg

Example of User Preferences

Time 0: Min. Rate = 0 Kb/s

weights = 1,2,3 for S0-S2

Priority -> S0 (max), S2(min)

Time 300: Min Rate = 600 Kb/s

TCP

BWSS


Slide17 l.jpg

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


Slide18 l.jpg

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)


Overview of the presentation19 l.jpg

Overview of the Presentation

  • Motivation

  • Goals

  • Proposed Method

  • NS-2 Simulations

  • Conclusion


Conclusion l.jpg

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 flow’s cwnd

    - What was receiver window advertisement actually designed for??


Observation tcp window management l.jpg

Data1 win4

2

Ack1 win4

4

3 4 5 6

DATA3 ~ 6 win4

8

Ack6 win2

9

DATA10 ~11 win4

10 11

Observation: TCP window management

sender

receiver

1


Slide22 l.jpg

Questions??


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