Network Performance Monitoring at Small Time Scales Dina

Network Performance Monitoring at Small Time Scales Dina Papagiannaki, Rene Cruz, Christophe Diot page 1 Advanced Technology Laboratories

Motivation • Network management for large-scale networks almost exclusively relies on SNMP. • SNMP reports on aggregate link activity for the duration of the polling interval (5 mins). • Operators provision their network around these values according to provider-specific “acceptable” utilization levels. Advanced Technology Laboratories 2

Questions • Can one infer delay “degradation” from SNMP link counters? • Can one infer delay performance from output link utilization? – At what time scale should these measurements be taken? • How do we summarize such high-resolution measurements in a 5 -minute counter? Advanced Technology Laboratories 3

Terminology A micro-congestion episode is a short-lived episode in the lifetime of a link when packets face increased delays due to crosstraffic. Metrics: Amplitude, Duration, Frequency Advanced Technology Laboratories 4

Measurement Data: Sampling the Output Queue • Collect packet traces from links attached to the same router (set 1: OC-3, set 2: OC-12) • Compute single-hop delay using GPS accurate timestamps for arrival and departure OC-3 Advanced Technology Laboratories 5

Methodology • Compute link throughput for non-overlapping time intervals of (1 ms, 100 ms, 1 s) duration • Collect all delay samples for each interval • Associate throughput level with delay distribution d 2 d 1 Advanced Technology Laboratories Output Link 6

Delay performance (OC-3) Advanced Technology Laboratories 7

Instantaneous link utilization and delay • Instantaneous link utilization may be high even when packets do not experience congestion! Advanced Technology Laboratories NO QUEUEING DELAY 8

5 minutes too long to capture micro-congestion 5 minutes Advanced Technology Laboratories 9

Inference of Duration and Frequency • If a micro-congestion episode persists in time, it should be visible across time scales • For each time scale τ we count the number of intervals exceeding θ throughput level • Measure fraction of overloaded intervals within each 5 minute interval Output link Advanced Technology Laboratories 10

Inference of Duration (cntd) • If the fraction of “congested” intervals exceeding θ at time scale τ+1 is greater than the fraction of “congested” intervals at time scale τ, then significant fluctuations at time scale τ. Reporting interval Advanced Technology Laboratories 11

Duration/Frequency Advanced Technology Laboratories 12

Summary • 5 minute average utilization measurements can hide micro-congestion episodes. • There is no unique time scale that captures microcongestion. • Impact needs to be studied at multiple time scales simultaneously. • New metric to address network performance monitoring at small time scales. Advanced Technology Laboratories 13

Ongoing Work • We need to identify the impact of – Link capacity – Traffic arrival pattern • We have instrumented an entire router and analyze busy periods. Advanced Technology Laboratories 14