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TCP/IP over 3G Wireless

Links with Rate and DelayVariation

M. Chan and R.Ramjee

Bell Labs, Lucent technologies

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Content

Introduction Outline of a model used here

Proposed solution(Ack Regulator) Outline of the simulation result for

using AR Conclusion(contributions and some left)

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Introduction

Wireless link losses result in poor TCPthroughput.

Added mechanisms add the Delay andRate variation at the same time

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Introduction

This paper proposed a model to explainthe impact of variable rate and delay on

long lived TCPs performance It proposed a solution to improve the

performance in 3G wireless network

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Model

This paper model the performance of asingle long lived TCP flow over a network(rate)with a single bottleneck server, and a

wireless link(delay). The model used here is an extension of a

model in ideal environment and constant rate

and delay.

Here the rate and delay both arechanged to variable.

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Model

Here are the figures and table they got:

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Model

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Ack Regulator

NamedAck regulator since it regulates theflow of acks back to the TCP source.

The solution is designed for improving theperformance of TCP flows towards the mobilehost

Implemented at the wireless edge, RNC,

Need a per-TCP-flow queue

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Ack Regulator

The implementation:

Run on every transmission of data and arrival of ack.

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Ack Regulator

The intuition: To avoid any buffer overflow loss until the congestion window at theTCP source reaches a pre-determined

threshold and beyond that, allow only asingle buffer over flow loss.

Therere two important variable:1.ConservativeMode2.AckReleaseCount

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Ack Regulator

The Ack Regulator algorithm:

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Ack Regulator

Therere two algorithms forConservativeMode and AckReleaseCount

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Simulation Result

It used the Topology as this:

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Simulation Result

Summary of the comparison:(Reno ,Sack vsAR)

1.

43% Reno, 19% Sack

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Simulation Result

2. Variable rate:

Throughput 15% Reno, same as Sack

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Simulation Result

3. Variable delay and rate:

22% Reno and 10% Sack

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Simulation Result

4.HDR variable rate and delay:

5% to 33% Reno and 0.5% to 24% Sack

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Simulation Result

5. Multiple flows sharing HDR:

32% Reno and 36% Sack

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Conclusion

Contribution: 1. Evaluated the impact of variable rate and variable

delay on long-lived TCP performance.

2. Proposed a model to explain and predict TCPsthroughput over a link with variable rate and/ordelay.

3. Proposed a network-based solution called AckRegulator

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Conclusion

Question left: Queue: Two kinds(dqueue and aqueue) and per-

TCP flow queue, maybe need more bandwidth( badstate!)

Big window used: 500KB, never window limited

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Thank you very much

Nice Weekend