Access Link Capacity Monitoring with TFRC Probe

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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

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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.

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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

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Potential Applications

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

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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

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Packet Pair Dispersion
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Ideal Packet Dispersion

• No cross-traffic

Capacity (Packet Size) / (Dispersion)
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Compression and Expansion

• First packet queueing ? compressed dispersion ?
  Over-estimation
• Second packet queueing ? expanded dispersion ?
  Under-estimation

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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

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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.

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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

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TFRC Probe

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

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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.

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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

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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.

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Simulation

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

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Simulation Results
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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.

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Experiment Results 1

• Wired Internet links (no pkt size adaptation)

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Experiment Results 2

• Wireless links (no pkt size adaptation)

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Experiment Results 3

• 802.11b link with varying data rate (with pkt
  size adaptation)

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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

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• Thanks!