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Access Link Capacity Monitoring with TFRC Probe

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Title: Access Link Capacity Monitoring with TFRC Probe


1
Access Link Capacity Monitoring with TFRC Probe
  • Ling-Jyh Chen, Tony Sun, Dan Xu, M. Y. Sanadidi,
    Mario Gerla
  • Computer Science Department, University of
    California at Los Angeles

2
Motivation
  • Knowledge of link capacity is important for
    network management, pricing, and QoS support.
  • The link capacity of a network connection may
    vary dramatically due to vertical handoff,
    dynamic channel allocation, and wireless channel
    quality.
  • Knowing the link capacity will permit the source
    to rapidly and appropriately adapt the outbound
    data transmissions rate.

3
Access Link Capacity Monitoring
  • Requirements
  • provide correct information
  • work passively without adding excess overhead
  • promptly react to occurrences in network events
  • maintain end-to-end semantics
  • Our approach TFRC Probe
  • embed CapProbe algorithm within TFRC
  • simple, accurate, passive, timely, and end-to-end
  • extensible to other protocols and applications

4
Potential Applications
  • Adaptive multimedia streaming
  • Congestion control
  • Overlay network structuring
  • Wireless link monitoring
  • Mobility detection

5
The Capacity Estimation Problem
  • Estimate minimum link capacity on an Internet
    path, as seen at the IP level
  • Design Goals
  • End-to-end assume no help from routers
  • Inexpensive Minimal additional traffic and
    processing
  • Fast converges to capacity fast enough for the
    application

6
Packet Pair Dispersion
7
Ideal Packet Dispersion
  • No cross-traffic

Capacity (Packet Size) / (Dispersion)
8
Compression and Expansion
  • First packet queueing ? compressed dispersion ?
    Over-estimation
  • Second packet queueing ? expanded dispersion ?
    Under-estimation

9
CapProbe
  • Filter PP samples that do not have minimum
    queuing time
  • Dispersion of PP sample with minimum delay sum
    reflects capacity
  • CapProbe combines both dispersion and e2e transit
    delay information
  • CapProbe is simple, fast, and accurate

10
TFRC TCP-Friendly Rate Control
  • TFRC is an equation based unicast multimedia
    streaming protocol.
  • TFRC mimics the TCP long-term throughput by
    utilizing the function
  • The receiver is responsible for calculating the
    loss event rate p and sending the information
    back to the sender once per round-trip time.
  • The sender is responsible for adjusting its
    sending rate Tactual to be close to T.

11
TFRC Probe
  • Embedding CapProbe within TFRCThree design
    issues
  • Accurate capacity estimation
  • Fast estimation process
  • Minimal traffic overhead and modification to the
    original TFRC
  • Two design options
  • One-way estimation
  • Round-trip estimation

12
TFRC Probe
  • Accurate Capacity EstimationEmbed CapProbe
    algorithm within TFRC by sending two packets
    back-to-back every n packets

13
TFRC Probe
  • Fast Link Capacity Estimation
  • Fast in estimating link capacities from
    samplesCapProbe has been shown to be a fast and
    accurate technique for link capacity estimation.
  • Fast in getting samplesThe speed of sampling
    will increase/decrease when the packet sizes
    decrease/increase.

14
TFRC Probe
Packet size adaptation
  • Rsend is the sending rate of data packets
  • S is the number of samples needed to get a
    reliable capacity estimation
  • P is the data packet size
  • t is the expected time to get one capacity
    estimation.
  • n is the number of data packets between samples

15
Simulation
  • The monitoring ability of TFRC Probe is verified
    using NS-2 simulator
  • The bottleneck link (between node 3 and 4) is
    shared by all the data flows and configured as an
    asymmetric link with various capacities in the
    forward direction and fixed capacity (100Kbps) in
    the backward direction.

16
Simulation
  • Three type of cross traffic are employed in the
    simulaiton.
  • The link capacity estimation results are
    collected after 20 and 50 samples.

17
Simulation Results
18
Experiments
  • Implementation based on the original TFRC codes
    (Linux platform)
  • Experiments
  • Without packet size adaptation
  • Evaluate the effectiveness of TFRC Probe in wired
    Internet links (symmetric and asymmetric links)
    and wireless links (1xRTT and 802.11b)
  • With packet size adaptation
  • Evaluate the feasibility of monitoring wireless
    link capacity using TFRC Probe.

19
Experiment Results 1
  • Wired Internet links (no pkt size adaptation)

20
Experiment Results 2
  • Wireless links (no pkt size adaptation)

21
Experiment Results 3
  • 802.11b link with varying data rate (with pkt
    size adaptation)

22
Conclusion
  • TFRC Probe is simple, accurate, passive, timely,
    and end-to-end.
  • The evaluation of TFRC Probe is performed by both
    simulation and testbed experiments.
  • The same concept can be applied to other UDP
    based application protocols (e.g. RAP, RTP, UDP
    based FTP and P2P file downloading) and other
    emerging data transmission protocols (e.g. DCCP).
  • CapProbe website http//nrl.cs.ucla.edu/CapProbe

23
  • Thanks!
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