1 1 cshcn, copyright © 2003 center for satellite & hybrid communication networks title:...

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1CSHCN, Copyright © 2003

Center for Satellite & Hybrid Center for Satellite & Hybrid Communication NetworksCommunication Networks

Title: Multipath Transport Protocol and Stability

Faculty: Richard J. LaStudents: Priya Rajan

Aashish Saxena

Industry Advisory BoardApril 10, 2003

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Overall GoalOverall Goal

• Objective: Design an efficient and stable transport layer protocol for networks with large delays

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Why?Why?

• Significance/Applications– Take advantage of multi-homing and multi-streaming

– Faster reaction to changes in network state

– Potential provisioning of differentiated services to multiple streams

– Stable network operation Especially with communication delay

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MethodologyMethodology

• Methodology– Rate control as a constrained optimization problem

– Choice of utility functions and resource price functions

sconstraint clustering

subject to

)( maximize

wHy

yAUi

ii

yHp jj

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IssuesIssues

• Problems– Design of end-user algorithms and resource pricing mechanisms

– Convergence of the algorithms Singularly perturbed system

– Stability of the system with communication delays Heterogeneous connections with widely varying round-trip delays Simple and robust algorithm design

– Delay-independent stability?

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So far …So far …

• Achievements– Convergence of reduced system with a family of utility

functions

– Characterized the stability conditions with arbitrary communication delay in a single bottleneck case with homogeneous (and heterogeneous) users Fundamental tradeoff between price elasticity of demand (responsiveness

of end users) and stability of the system Tradeoff between resource utilization and stability

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• Utility functions:

– The larger a is, the less elastic the demand is

– Strictly concave increasing

• Price functions:

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b

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1

)(

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• End-user algorithm

• System (single resource) is stable with an arbitrary delay if

for all users sufficient conditions – not necessary

• Non-responsive flow improves system stability

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)])(()())(()([)( '

jjiiiii TtxpTtxtxUtxtx

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What do we expect…What do we expect…

• Expected Results– Convergence of the overall system with multipath

Needs convergence of both reduced and boundary layer system

– Characterization of the stability of the system with heterogeneous users with arbitrary communication delay with multiple resources Interaction of users with different utility functions Characterization of stability in the presence of non-responsive flow

– Simple analysis shows enhanced stability

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What is to come…What is to come…

• Plans for Upcoming Year– long term

Demonstration of convergence of the algorithm without and with feedback delay

Development (on simulation testbed) of multipath capable transport layer protocol

Characterization of the stability conditions and fundamental tradeoffs between stability and elasticity

– Provide design guidance for end-user algorithm and AQM mechanisms

– short term Convergence of multipath algorithm without feedback delay Guideline for selection of utility and price functions

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PublicationsPublications

• List Publications/Presentations– “Delay, elasticity, and stability trade-offs in rate control” by P. Ranjan, E. H.

Abed, and R. J. La – submitted to IEEE Globecom 2003

– “Communication delay and instability in rate-controlled networks” by P. Ranjan, E. H. Abed, and R. J. La – submitted to IEEE CDC 2003

– “Limiting model of ECN/RED under a large number of heterogeneous TCP flows”, by P. Tinnakornsrisuphap, and R. J. La - submitted to IEEE CDC 2003

– “Instability of a tandem network and its propagation under RED” by R. J. La – to appear in the proc. of IEEE ICC 2003

– “Characterization of general TCP traffic under a large number of flows regime” by P. Tinnakornsrisuphap, R. J. La, and A. M. Makowski – to appear in the proc. of CTA C&N Annual Symposium 2003

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