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Practical Issues in Internet Measurement

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? .

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Practical Issues in Internet Measurement

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

  2. Where Can Measurements Be Made? IXP

  3. Where Can Measurements Be Made? • Local Area Network • Local testbeds • Complete control, precise measurements

  4. 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.

  5. 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

  6. Where Can Measurements Be Made? • Internet Exchange Point (IXP) • Free or Fee-based • traffic patterns • ensure locality

  7. 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

  8. 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

  9. 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

  10. 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)

  11. Role of Internet Directories and Databases

  12. Role of Internet Directories and Databases • Domain Name System • Measurement related issues in dealing with databases • Out-of-date • Old cache

  13. 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

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