1
Center for Satellite & Hybrid
Communication Networks
Title: Multipath Transport Protocol
and Stability
Faculty:
Students:
Richard J. La
Priya Rajan
Aashish Saxena
Industry Advisory Board
April 10, 2003
CSHCN, Copyright © 2003
1
2
Overall Goal
• Objective: Design an efficient and stable transport
layer protocol for networks with large delays
CSHCN, Copyright © 2003
2
3
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
CSHCN, Copyright © 2003
3
4
Methodology
• Methodology
– Rate control as a constrained optimization problem
maximize
U ( A y)
i
i
i
subject to
Hy  w
clustering constraint s
– Choice of utility functions and resource price functions
p j H j y 
CSHCN, Copyright © 2003
4
5
Issues
• 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?
CSHCN, Copyright © 2003
5
6
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
CSHCN, Copyright © 2003
6
7
So far …
• Utility functions:
U a ( x) 
1
a  xa
– The larger a is, the less elastic the demand is
– Strictly concave increasing
• Price functions:
 z 
p j z    
C 
 j
b
, b0
CSHCN, Copyright © 2003
7
8
So far …
• End-user algorithm

x i (t )   [ xi (t )U i' ( xi (t ))  xi (t  T ) p( x j (t  T ))]
j
• System (single resource) is stable with an arbitrary
delay if
for all users
ai  b  1
 sufficient conditions – not necessary
• Non-responsive flow improves system stability
CSHCN, Copyright © 2003
8
9
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
CSHCN, Copyright © 2003
9
10
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
CSHCN, Copyright © 2003
10
11
Publications
• 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
CSHCN, Copyright © 2003
11