Endtoend Asymmetric Link Capacity Estimation

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End-to-end Asymmetric Link Capacity Estimation

• Ling-Jyh Chen, Tony Sun, Guang Yang, M.Y.
  Sanadidi, Mario Gerla
• Dept. of Computer Science, University of
  California at Los Angeles

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Definition

• Capacity maximum IP-layer throughput that a flow
  can get, without any cross traffic.
• Available Bandwidth maximum IP-layer throughput
  that a flow can get, given (stationary) cross
  traffic.

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Previous Work on Capacity Estimation

• Per-hop based
• pathchar use different packet sizes to probe the
  per-hop link capacity
• clink, pchar variants of pathchar
• Nettimer use packet tailgating technique
• End-to-end based
• Pathrate, Sprobe, CapProbe
• These approaches are either one-way based or
  unable to estimate asymmetric link capacities.

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Estimating Asymmetric Links

• Asymmetric links are becoming popular (e.g. DSL,
  cable modems, and satellite links).
• Knowing the capacity of BOTH direction links is
  important for applications.
• Related work
• ALBP Yu et al, ICC03 employs a multi-packet
  delay model to estimate per-hop capacity of
  asymmetric links.

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Our Contribution

• We propose an end-to-end asymmetric link capacity
  estimation technique, called AsymProbe.
• AsymProbe is CapProbe based
• round trip method
• packet pair based
• simple, fast, and accurate

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

• Queueing delay on the first packet gt
  compression
• Queueing delay on the second packet gt expansion

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CapProbe (Rohit et al, SIGCOMM04)

• Key insight a packet pair that gets through with
  zero queueing delay yields the exact estimate.
• CapProbe uses Minimum Delay Sum filter.

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Proposed Approach AsymProbe
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AsymProbe Example
CP/T
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AsymProbe Algorithm

• AsymProbe has four phases
• Phase 1 the probing phase (P1Pmax P2Pmax )
  (gt CapProbe)
• Phase 2 the probing phase (P1Pmax P2Pmin)
• Phase 3 the probing phase (P1Pmin P2Pmax )
• Phase 4 the decision phase

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AsymProbe Algorithm

• The decision phase

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Issues

• AsymProbe is able to estimate asymmetric link
  capacities when the asymmetric ratio is larger
  than Pmin /Pmax and smaller than Pmax /Pmin.
• AsymProbe can not estimate extremely asymmetric
  links.
• Pmax is limited by MTU.
• Pmin is limited by the supported system time
  resolution.

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Simulation

• AsymProbe A lt-gt B Cross Traffic C lt-gtB
• E-gtD 1.5Mbps D-gtE 128kbps

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Simulation Results

• Pmax1500 bytes Pmin100 bytes

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Emulation

• Pmax1500 bytes Pmin500 bytes

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Emulation Results
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Internet Experiments

• P11500 bytes, P2500 bytes
• Supported asymmetric ratio 31

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Application TCP Probe

• The concept of AsymProbe can be integrated with
  other data transmission protocols, e.g. TCP.
• TCP packet size
• forward direction TCP data 1500 bytes
• reverse direction TCP ACK 40 bytes
• According to AsymProbe algorithm
• If , then T1gtT2 TCP Probe estimates
  the capacity of the forward direction link
• If , then T1ltT2TCP Probe estimates
  the capacity of the reverse direction link

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TCP Probe

• More details in Anders et al, GI05

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TCP Probe Application

• Vertical handoff usually results in a dramatic
  change in the path capacity.
• Service agility using Fast Rate Adaptation
  (FRA) algorithm
• FRA forces TCP to enter Slow Start when detecting
  a handoff from LOW to HIGH

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Service Agility TCP Probe

• TCP Probe with fast rate adaptation
• Vertical handoff from 10Mbps to 100Mbps

Unit bps
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Summary

• We propose an end-to-end asymmetric link capacity
  estimation technique, called AsymProbe.
• We evaluate AsymProbe by simulation and Internet
  experiments.
• The concept of AsymProbe can be integrated with
  other data transmission protocols.
• We present a passive capacity estimation
  technique, called TCP Probe, which integrates
  AsymProbe with TCP.

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Thanks!
CapProbe http//nrl.cs.ucla.edu/CapProbe/