Evaluating pathrate and pathload with realistic cross-traffic Ravi Prasad Manish Jain Constantinos Dovrolis (ravi, jain, dovrolis@cc.gatech.edu) College of Computing Georgia Institute of Technology Bandwidth Estimation Workshop 2003
Background ! Pathrate ! Estimates path capacity ! Based on packet pair/train dispersion ! Packet pair estimates: Set of possible capacity modes ! Packet train estimates: ADR=Lower bound on capacity ! Capacity = (Strongest and narrowest mode > ADR) ! Pathload ! Estimates path available bandwidth (avail-bw) ! Based on one-way delay trend of periodic streams ! Reports a range of avail-bw ! Corresponds to variation, measured in stream duration ! http://www.pathrate.org Bandwidth Estimation Workshop 2003
Motivation ! Recent studies pointed towards poor accuracy of these tools ! http://www.caida.org/outreach/presentations/200 3/bwest0308/doereview.pdf ! A measurement study of available bandwidth estimation tools . Strauss et. al. IMC 2003 ! Our objective: re-evaluate accuracy of both tools ! Wide range of cross-traffic load ! Realistic cross-traffic ! Completely monitored testbed (no guessing!) Bandwidth Estimation Workshop 2003
Outline ! Describe test methodology ! Testbed ! Cross-traffic type ! Show accuracy results ! 100Mbps path ! 1Gbps path ! With Iperf cross-traffic ! Explaining inaccuracies with Iperf cross- traffic ! Conclusions Bandwidth Estimation Workshop 2003
Testing methodology ! Used local testbed ! Complete knowledge of path properties ! Capacity ! Available bandwidth ! Complete control of cross-traffic ! Rate ! Type (TCP vs UDP vs trace-driven) Bandwidth Estimation Workshop 2003
Testbed Measurement Traffic C Workgroup Switch Workgroup Switch 1 Gbps Catalyst 1 Gbps Catalyst CiscoSystems CiscoSystems Cross−traffic ! Narrow link capacity C = 100Mbps or 1Gbps Bandwidth Estimation Workshop 2003
Cross traffic ! Trace-driven cross-traffic generation: ! NLANR traces ! OC-3, OC-12, OC-48 Trace information at the end of the talk ! ! Packet size distribution ! Unmodified ! Packet interarrivals ! Either, scaled to achieve desired cross-traffic throughput ! Or, unmodified ! Iperf-based cross-traffic ! Single TCP stream ! UDP stream Bandwidth Estimation Workshop 2003
Results Bandwidth Estimation Workshop 2003
FastEthernet: Traces with scaled interarrivals 100 80 Estimated bandwidth (Mbps) 60 40 Pathrate 20 Pathload Capacity Avail bw 0 0 20 40 60 80 100 Cross-traffic utilization (Mbps) Bandwidth Estimation Workshop 2003
FastEthernet: Traces with unmodified interarrivals 100 80 Estimated bandwidth (Mbps) 60 40 Pathrate 20 Pathload Capacity Avail bw 0 0 20 40 60 80 100 Cross-traffic utilization (Mbps) Bandwidth Estimation Workshop 2003
Gigabit path: Traces with scaled interarrivals 1000 800 Estimated bandwidth (Mbps) 600 400 Pathrate 200 Pathload Capacity Avail bw 0 0 200 400 600 800 1000 Cross-traffic utilization (Mbps) Bandwidth Estimation Workshop 2003
Unrealistic cross-traffic ! Single stream TCP T R ! Entire window appears as T W burst at beginning of RTT ! Minimum averaging interval: RTT ! UDP periodic stream ! Packet size: L L/C ! Rate: R ! Dispersion: L/R ! Utilization ρ = R/C L/R Bandwidth Estimation Workshop 2003
Gigabit Path: Iperf Periodic UDP 1000 800 Estimated bandwidth (Mbps) 600 400 Pathrate 200 Pathload Capacity Avail bw 0 0 200 400 600 800 1000 Cross-traffic utilization (Mbps) Bandwidth Estimation Workshop 2003
Pathrate under unrealistic traffic ! Seeks some “off” time periods T R of duration larger than L/C T W T O ! L: Probe size ! TCP traffic ! Off period T O =T R - T W - L/C ! Correct capacity estimate when T O > L/C ! UDP periodic traffic L/C ! If ρ < 0.5 then T O > L/C ! Else, underestimation L/R Bandwidth Estimation Workshop 2003
Gigabit path: Iperf single stream TCP 1000 800 Estimated bandwidth (Mbps) 600 400 Pathrate 200 Pathload Capacity Avail bw 0 0 200 400 600 800 1000 Cross-traffic utilization (Mbps) Bandwidth Estimation Workshop 2003
Pathload under unrealistic traffic ! Samples avail-bw in T R stream duration (T S ) T W T S T S T S ! TCP traffic ! Avail-bw averaging period T R ! T S << T R results in wide Avail-bw range estimate ! UDP periodic traffic L/C ! Avail-bw averaging period T S L/R ! T S = 100 x L/C > L/R ! Correct avail-bw range estimate L/R Bandwidth Estimation Workshop 2003
Conclusions ! Type of cross-traffic is important for bandwidth estimation tools ! Pathrate and pathload perform well with realistic cross-traffic ! Simulated traffic does not capture: ! Packet size distribution ! Interarrival distribution ! Correlation structure Bandwidth Estimation Workshop 2003
Trace identifiers ! OC3 : MEM-1070464136-1, COS-1070488076-1, BWY-1063315231-1, COS-1049166362-1 ! OC12: MRA-1060885637-1 ! OC48: IPLS-CLEV-20020814-093000-1 ! We greatly appreciate the availability of traces from NLANR PMA project. The NLANR PMA project is supported by National Science Foundation Cooperative agreement nos. ANI-0129677 (2002) and ANI-9807479 (1998). Bandwidth Estimation Workshop 2003
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