Practical Issues in Internet Measurement
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Practical Issues in Internet Measurement adapted from Mark Crovella and Balachander Krishnamurthy
description
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
Transcript of Practical Issues in Internet Measurement
Practical Issues in Internet Measurement
adapted fromMark 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?
• 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.
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
Where Can Measurements Be Made?
• Internet Exchange Point (IXP)– Free or Fee-based– traffic patterns– ensure locality
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
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
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
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)
Role of Internet Directories and Databases
Role of Internet Directories and Databases
• Domain Name System
• Measurement related issues in dealing with databases– Out-of-date– Old cache
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
