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Evaluating pathrate and pathload with realistic cross-traffic. Ravi Prasad Manish Jain Constantinos Dovrolis (ravi, jain, [email protected]) College of Computing Georgia Institute of Technology. Background. Pathrate Estimates path capacity Based on packet pair/train dispersion

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Evaluating pathrate and pathload with realistic cross traffic

Evaluating pathrate and pathload with realistic cross-traffic

Ravi Prasad

Manish Jain

Constantinos Dovrolis

(ravi, jain, [email protected])

College of Computing

Georgia Institute of Technology


Background
Background cross-traffic

  • 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


Motivation
Motivation cross-traffic

  • Recent studies pointed towards poor accuracy of these tools

    • http://www.caida.org/outreach/presentations/2003/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!)


Outline
Outline cross-traffic

  • 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


Testing methodology
Testing methodology cross-traffic

  • Used local testbed

    • Complete knowledge of path properties

      • Capacity

      • Available bandwidth

    • Complete control of cross-traffic

      • Rate

      • Type (TCP vs UDP vs trace-driven)


Testbed
Testbed cross-traffic

  • Narrow link capacity C = 100Mbps or 1Gbps


Cross traffic
Cross traffic 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


Results

Results cross-traffic


Fastethernet traces with scaled interarrivals
FastEthernet: cross-trafficTraces with scaled interarrivals


Fastethernet traces with unmodified interarrivals
FastEthernet: cross-trafficTraces with unmodified interarrivals


Gigabit path traces with scaled interarrivals
Gigabit path: cross-trafficTraces with scaled interarrivals


Unrealistic cross traffic

T cross-trafficR

TW

L/C

L/R

Unrealistic cross-traffic

  • Single stream TCP

    • Entire window appears as burst at beginning of RTT

    • Minimum averaging interval: RTT

  • UDP periodic stream

    • Packet size: L

    • Rate: R

    • Dispersion: L/R

    • Utilization r = R/C


Gigabit path iperf periodic udp
Gigabit Path: cross-trafficIperf Periodic UDP


Pathrate under unrealistic traffic

T cross-trafficR

TW

TO

L/C

L/R

Pathrate under unrealistic traffic

  • Seeks some “off” time periods of duration larger than L/C

    • L: Probe size

  • TCP traffic

    • Off period TO =TR - TW- L/C

      • Correct capacity estimate when TO > L/C

  • UDP periodic traffic

    • If r< 0.5then TO > L/C

    • Else, underestimation


Gigabit path iperf single stream tcp
Gigabit path: cross-trafficIperf single stream TCP


Pathload under unrealistic traffic

T cross-trafficR

TW

TS

TS

TS

TS

L/C

L/R

Pathload under unrealistic traffic

  • Samples avail-bw in stream duration (TS)

  • TCP traffic

    • Avail-bw averaging period TR

    • TS << TR results in wide Avail-bw range estimate

  • UDP periodic traffic

    • Avail-bw averaging period L/R

    • TS = 100 x L/C > L/R

    • Correct avail-bw range estimate


Conclusions
Conclusions cross-traffic

  • 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


Trace identifiers
Trace identifiers cross-traffic

  • 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).


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