practical issues in internet measurement

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Practical Issues in Internet Measurement adapted from Mark Crovella and Balachander Krishnamurthy

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Practical Issues in Internet Measurement. adapted from Mark Crovella and Balachander Krishnamurthy. Where Can Measurements Be Made? . IXP. Where Can Measurements Be Made? . Local Area Network Local testbeds Complete control, precise measurements. Where Can Measurements Be Made? . - PowerPoint PPT Presentation

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Page 1: Practical Issues in Internet Measurement

Practical Issues in Internet Measurement

adapted fromMark Crovella and Balachander Krishnamurthy

Page 2: Practical Issues in Internet Measurement

Where Can Measurements Be Made?

IXP

Page 3: Practical Issues in Internet Measurement

Where Can Measurements Be Made?

• Local Area Network– Local testbeds– Complete control, precise measurements

Page 4: Practical Issues in Internet Measurement

Where Can Measurements Be Made?

• Inside a backbone– Routine measurements• ensure availability• scan for outages or attacks• topology changes• compliance with SLAs• traffic trends

– Inra-AS measurements• SNMP: Simple Network Management Protocol• Provisioning

– macro: traffic shifts– micro: setting parameters of gateways etc.

Page 5: Practical Issues in Internet Measurement

Where Can Measurements Be Made?

• Entry points into a network– Gateway routers• NetFlow or sFlow

– Peering routers• BGP• Public or Private

– IXP to direct links• might trigger policy changes• improve paths

– Access routers• residential customers to commercial servers• performance monitoring• SLA

Page 6: Practical Issues in Internet Measurement

Where Can Measurements Be Made?

• Internet Exchange Point (IXP)– Free or Fee-based– traffic patterns– ensure locality

Page 7: Practical Issues in Internet Measurement

Where Can Measurements Be Made?

• Wide Area Network– various places in the network– multi-site measurements• simultaneous or over a period of time• PlanetLab, M-Lab, RIPE Atlas, Ark, …

– Representativeness• Keynote

Page 8: Practical Issues in Internet Measurement

Role of Time in Measurements

• Capturing time accurately– True time t– Reported time C(t)– Offset: θ(t) = C(t) - t– Rate: First derivative of apparent time to true time• ϒ(t) = dC(t)/dt

– Skew: Difference between its rate and correct time• skew = ϒ - 1

– Resolution: Smallest amount by which C(t) can change

– Accuracy is more stringent requirement than zero skew and is harder to obtain

– Resolution requirements diminish higher in protocol stack

Page 9: Practical Issues in Internet Measurement

Role of Time in Measurements

• Sources of Time Information– External Time Sources• Radio clocks, GPS, CDMA

– PC based clocks • Hardware clock and Software clock• Time Stamp Counter

• Synchronized Time– Synchronized clocks• Network Time Protocol

– Synchronizing measured times after the fact• relative skew and offset

Page 10: Practical Issues in Internet Measurement

Role of Internet Directories and Databases

• Address registries• Domain Name System (DNS)

• Internet Address and Routing Registries– Internet Assigned Numbers Authority (IANA)

– Internet Routing Registry• Clearinghouse for AS number mapping

– Regional Internet Registries (RIR)

Page 11: Practical Issues in Internet Measurement

Role of Internet Directories and Databases

Page 12: Practical Issues in Internet Measurement

Role of Internet Directories and Databases

• Domain Name System

• Measurement related issues in dealing with databases– Out-of-date– Old cache

Page 13: Practical Issues in Internet Measurement

Measurement Across Various Layers

• Issues in capturing data– Lower-level protocol data– Gathering packet traces and flows– Application level data gathering

• Changes to Infrastructure/Instrumentation

• Local vs Remote vs Distributed data gathering

• Measurement on Overlays