Application-level versus Network-level Application-level versus Network-level Proximity Proximity

Mohammad Malli

PhD student Planete Project,

INRIA - Sophia Antipolis France

December 15, 2005 2

Introduction

• In P2P and CDN, the characterization of the proximity is very

important for identifying the best peer to contact or to take as

neighbor

• Our problem is to study how to characterize efficiently this

proximity

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Motivation

• Most of existing protocols rely on the delay for characterizing

the proximity of peers

• Using the delay closest peer as the best peer hides the implicit

assumption that the path with the nearest peer has the largest

available bandwidth and the smallest loss rate

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Questions

Q1. is the delay correlated with other network path parameters ?

Q2. does its use approximate the use of the others ?

Q3. How much is the performance degradation for applications

relying on the delay proximity ?

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Measurement scenario

• We try to answer these questions using measurements runned

over the Planetlab plateform.

• 127 nodes, spread over the Internet covering America,

EU, and Asia, are used.

• The network characteristics is measured for more than 16k

paths.

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Delay vs. available bandwidth

• 12 % of peers have the maximum available bandwidth on their path with the nearest peer

• Correlation coefficient between these two parameters is – 0.096

• Slow decrease of the available bw with the delay-based peer rank

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Delay vs. loss rate

• 88 % of peers have the minimum loss rate on their path with the nearest peer

• When moving farer in the delay space, the loss rate increases rapidely

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Impact of delay proximity on application performance

• The weak correlation obtained between the delay and the

other path parameters motivates us to evaluate the

performance degradation of applications when the proximity

is characterized based on the delay alone

• To this end, we consider two typical applications

• File transfer over TCP

• Interactive audio service

December 15, 2005 9

File transfer over TCPWe compute the degradation of the transfer time compared to the optimal ranking :

File size increases => degradation increases

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od

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Interactive audio serviceWe compute the speech rating factor :

Delay proximity => medium audio quality for the 7 closest peers and low quality for the remaining 3 others

ed IIRR 0

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Conclusions

• Delay is a poor predictor for quality for many applications

• This can be interpreted by the low correlation obtained

between the delay and the other network path parameters

• Now, we focus on how to deploy the application-level

proximity without loosing the scalability

December 15, 2005 12

Thank youThank you

Q & A

Mohammad.Malli@sophia.inria.fr