a fair and dynamic load balancing mechanism f. larroca and j.l. rougier

A Fair and Dynamic Load Balancing Mechanism

F. Larroca and J.L. Rougier

International Workshop on Traffic Management and Traffic Engineering for the Future Internet

Porto, Portugal, 11-12 December, 2008

Agenda

IntroductionUtility Maximization Load-BalancingDistributed AlgorithmSimulations

• Packet-Level Simulations• Fluid-Level Comparison

Conclusions

F. Larroca and J.L. Rougier FITRAMEN 08, Dec. 2008

Introduction

Network Convergence:• Traffic increasingly unpredictable and dynamic

Classic TE techniques (i.e. over-provisioning) inadequate: • Ever-increasing access rates• New emerging architectures with low link capacities

Possible answer: Dynamic Load-Balancing• Origin-Destination (OD) pairs with several paths:

how to distribute its traffic?• Paths configured a priori and distribution dependent

on current TM and network condition

page 3 F. Larroca and J.L. Rougier FITRAMEN 08, Dec. 2008

Introduction

Network operator interested OD pairs obtained performance• Why not state the problem in their terms?

Analogy with Congestion Control (TCP):• End-hosts = OD pairs• Rate = OD performance indicator

Differences: • Decision variable: portion of traffic sent through each

path (total traffic is given)• Much larger time-scale


Introduction

Previous proposals: • Define a link-cost function ll for each link l=1..L• Minimize the total network’s cost

Limitations: • Indirect way of proceeding• Cannot prioritize an OD pair or enforce fairness


Example:

Agenda



Conclusions


Utility Maximization Load-Balancing

Define a single performance indicator per OD pair• us(d): performance perceived by OD pair s when

traffic distribution is d “Distribute” us(d) among OD pairs to maximize total

Utility (à la Congestion Control)

• ds = total demand of OD pair s (given)• dsi = traffic sent through path i of OD pair s (∑dsi= ds)• d = [ d11 d12 .. dS1 .. dSnS ]T

How to define us(d)?


S

ssss

dduUd

1

))((max


Our choice for us(d): mean path’s Available Bandwidth (ABW)

Assumptions: • Majority of traffic is elastic (i.e. TCP)• Path choice considered propagation delay

Advantages: • Mean ABW rough approximation of rate obtained by

TCP flows (ABW is the most important indicator)• Sudden increases in demand may be

accommodated


lsil

sisisis ABWpABWp(d)u minarg


Final version of the problem:

If ABWsi is the flow obtained rate, the problem is very similar to Multi-Path TCP• By only changing ingress routers, users may be

regarded as if they used MP-TCP: improved performance and more supported demands


s

s

n

issi

S

s

n

isisiss

d

sdddcRdts

ABWpUd

1

1 1

,0,..

max

Agenda



Conclusions


Distributed Algorithm

The optimization problem is not convex However, not too “unconvex” The distributed algorithm solves the dual problem

and results in a good approximation Based on the Harrow-Hurwitz method: greedy on

path utility (PU) minus path cost (PC)


otherwise ,0

minarg if ),('

and ˆ where

ˆ)('

:

lsil

lsi

sil

s silisill

sillsisissi

ABWlABWUd

PCABWuUPU

Agenda



Conclusions


Packet-Level Simulations

A simple example: all links have the same capacity and probabilities are updated every 50 seconds


Comparison with two previous proposals: • MATE: minimize total M/M/1 delay

• TeXCP: greedy on the path’s maximum utilization

Two performance indicators: • Mean ABW (us) (weighted mean, 10% quantile and

minimum)• Link Utilization (mean, 90% quantile and maximum)

Fluid-Level Simulations


In two real topologies and TMs:

l lABW

1min

Mean ABW (us)

Link Utilization

UM/MATE

Fluid-Level Simulations – Abilene


UM/TeXCP

TeXCP - MATE TeXCP - UM

Fluid-Level Simulations – Géant Mean ABW (us)

Link Utilization


UM/MATE UM/TeXCP

TeXCP - MATE TeXCP - UM

Agenda



Conclusions


Conclusions

Performance as perceived by OD pairs is always better in UM than in MATE or TeXCP• MATE: relatively small differences in mean, but

significant in the worst case• TeXCP: more significant differences

Link utilization results for TeXCP and UM are very similar• MATE: although similar in mean and quantile, the

maximum link utilization may increase significantly Future Work:

• Stability• Other simpler methods or objective function that obtains

similar results


Thank youQuestions?


a fair and dynamic load balancing mechanism f. larroca and j.l. rougier

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