Measurement in the Internet Measurement in the Internet

Paul Barford

University of Wisconsin - Madison

Spring, 2001

WhyWhy measure the Internet? measure the Internet?

The size, growth, complexity and diversity of the Internet make it impossible to understand, manage, protect or provision without measurement.

Prior measurement studies have taught us a great deal– Self-similarity of packet traffic– Ubiquity of power laws

Businesses use measurements to provision, manage and operate

Future developments will require more and/or different measurements

WhatWhat can be measured in the can be measured in the Internet?Internet?

Structure– Topology, routing, CDN’s, wireless, etc.

Traffic– Transport, end-to-end performance, etc.

Users and Applications– WWW, (x,my)Napster, Peer-to-Peer,Streaming, security, etc.

Failures– In all areas

Nefarious behavior– Pattern attacks, port scans

WhereWhere are measurements made in are measurements made in the Internet?the Internet?

For some measurements, this is obvious– Web logs

The goal for other measurements is to be “representative”– Various “Internet weather reports”

Placement of measurement nodes is not a well understood problem– More is better??

HowHow are Internet measurements are Internet measurements made?made?

Passive methods– Application monitors (logs), packet monitors

Active methods– Probes, application simulation

SurveysSignificant infrastructure is always requiredAll methods present difficulties

WhenWhen must Internet must Internet measurements be made?measurements be made?

Diurnal traffic cycleTime scales depend on “what” and “how”Passive measurements are typically continuous

– Can generate huge data sets– Many people will not allow access to their logs

Active measurements are typically discrete– Important characteristics can be missed– Probes can be filtered and/or detected

WhoWho is doing Internet is doing Internet Measurements?Measurements?

Businesses do a great deal of measurement– What measurements are they taking and what do they

do with their data?Instrumentation for measurement-based research

is relatively new– Developments over the past 12 years have been slow– 10’s of current studies (see CAIDA and SLAC pages

for lists of these)Most studies are not coordinated and relatively

narrowly focused

In the past…In the past…

Bellcore Ethernet packet traces – Leland et al.– High time resolution LAN data collected over 4 year

period beginning in 1989– Thorough analysis showed self-similar properties

NPD study – Paxson– Characterized routing and packet behavior in wide area– First installation of large measurement infrastructure

Internet topology: Skitter ProjectInternet topology: Skitter Project

CAIDAInternet topology measurement infrastructures

– Traceroute studies focused on router/link discovery– Skitter: 17 sources, 54,000 destinations world wide– Data from Skitter is publically available

www.caida.org

Skitter example – BGP pathsSkitter example – BGP paths

SurveyorSurveyor

Advanced Network SystemsInfrastructure for measuring one-way Internet

latency, loss and routes between hosts– 61 sites world wide– GPS enabled– Closed platform (until recently)

www.advanced.org

Surveyor example - delaySurveyor example - delay

Wide Area Web Measurements Wide Area Web Measurements (WAWM)(WAWM)

Barford and Crovella (Wisconsin & Boston Univ.)Application level measurement infrastructure

– 11 clients (national and international)– GPS enabled

Combined passive and active measurementsApplication of critical path analysis to TCP

transactions www.cs.wisc.edu/~pb

Example of WAWM resultsExample of WAWM results

File transfer delay for 500KB file between Denver and Boston

National Internet Measurement National Internet Measurement Infrastructure (NIMI)Infrastructure (NIMI)

Paxson (ACIRI), Adams and Mathis (PSC)Secure management platform for wide area

measurements– Designed for general probe installation

Distributed client infrastructure– Principally academic sites (currently 41 world wide)

A number of projects are running on NIMIwww.ncne.nlanr.net

Short Term Challenges of Short Term Challenges of Internet MeasurementInternet Measurement

Developing methods for gathering more precise data– Current tools are frequently quite poor

Developing methods for analyzing measurement data more thoroughly– What we know about how things work is limited

Developing methods for understanding causes and effects across multiple domains

The future – Global Internet The future – Global Internet Measurement (GIM)Measurement (GIM)

Ubiquitous measurement capability– Embedded into the design of the Internet– Emphasis on extensible API’s for measurement– Analysis capability must be built in

Measurement quality and soundness Data formats that enable aggregation that reflects higher level behaviors

Many difficulties– Management, security, privacy, heterogeneity, deployment, etc.

See Performance Evaluation vol. 864 www.elsevier.com/locate/peva

ConclusionConclusion

Measurements are necessary for understanding Internet structure and behavior– Rule #1: Expect surprises!

Internet measurements are difficult– Rule #2: Expect the data to be “dirty”

Measurements are necessary for populating and validating any reasonable Internet models– Rule #3: Garbage-in-garbage out

Current measurement infrastructures can provide a great deal of data but fall short of the GIM goal