Performance Limitations of ADSL Users:A Case Study

Matti Siekkinen, University of Oslo

Denis Collange, France Télécom R&D

Guillaume Urvoy-Keller, Ernst W. Biersack,Institut Eurecom

PAMApril 6, 2007

April 21, 2023

Outline

Introduction Motivation Techniques for root cause analysis of TCP throughput

Measurement setup Analysis results Conclusions

April 21, 2023

Introduction

What? Analyzed 24h packet trace from France Telecom’s ADSL access network Studied throughput limitations experienced by clients

Why? Knowing throughput limitations (=performance) is useful

o ISPs want satisfied clientso Need to know what’s going on before things can be improved

How? Root Cause Analysis of TCP Throughput

o Analysis and inference of the reasons that prevent a given TCP connection from achieving a higher throughput.

o Passive traffic analysis Why TCP?

o TCP typically over 90% of all traffic

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Background

“On the characteristics and origins of Internet flow rates” by Zhang et al. (SIGCOMM 2002) Pioneering research work Congestion is not always the cause for throughput limitations

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Limitation Causes for TCP Throughput

Application The application does not even attempt to use all network resources E.g. streaming applications and “bursty” applications (Web browsing)

Transport layer TCP receiver

o Receiver advertized window limits the rateo max amount of outstanding bytes = min(cwnd,rwnd)o Flow controlo Configuration issue

• default receiver advertized window is set too low• window scaling is not enabled

TCP protocolo Ramp-up period in slow start and congestion avoidance

Network layer Congestion at a bottleneck link

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Measurement Setup

24 hours of traffic on March 10, 2006 Passively capture all TCP/IP headers analyze offline

290 GB of TCP traffic 64% downstream, 36% upstream

Observed packets from ~3000 clients, analyze only 1335 Excluded clients did not generate enough traffic for RCA

Two pcap probes here

Internetcollectnetwork

accessnetwork

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Connections Size distribution highly skewed Use only 1% of the flows for RCA

o Represent > 85% of all traffic

Clients Heavy-hitters: 15% of clients generate 85-90% of traffic (up &

down) Low access link utilization

Warming up…

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Results of Limitation Analysis

Few active clients overall Application limitation dominates Network limitation by distant bottleneck also experienced

containsmost bytes

containssome bytes

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Application analysis:Application limited traffic

Quite stable and symmetric volumes Vast majority of all traffic

eDonkey and “other” dominateP2P

other

eDonkey

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Application analysis:Saturated access link

No recognized P2P Asymmetric port 80/8080 downstream

Real Web traffic?

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Impact of Limitation Causes

How far from optimal (access link saturation) are we? Main observations

Very low downlink utilization for application limited traffico Utilization < 20% during 65% of application limited periods of traffic

Uplink utilization < 50% during most of application and network limited uploads

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Connecting the evidence…

Most clients’ performance limited by applications Very low link utilizations for application limited traffic Most of application limited traffic seems to be P2P

Peers often have asymmetric uplink and downlink capacities P2P applications/users enforce upload rate limits

Poor aggregate download performance

Internet

Internet

Low downlinkutilization Low uplink capacity

+rate limiter

downloading client

uploadingclients

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Conclusions

Analyzed 24h packet trace from France Telecom’s ADSL access network Studied throughput limitations experienced by clients

Majority of clients mostly throughput limited by applications P2P clients throttle upload rate

o Too much? Asymmetric link capacities

Impact and implications ISP traffic is mostly application limited traffic Things can change dramatically with

o More intelligent P2P clientso Caches

April 21, 2023

For the future…

Play with time scale Extended case study on ADSL clients

We saw a day, what about a week?

Could we do things on-line? Improving RCA techniques

Short connections Non FIFO traffic (e.g. wireless)

Thank you for your attention