Measuring Bandwidth

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Measuring Bandwidth

• K. Lai and M. Baker
• Presented by
• Cristina Abad

2
Outline

• Motivation
• Definitions
• Current Techniques
• Packet Pair
• Bandwidth Measurement Algorithms
• Potential Bandwidth Filtering
• Simulations
• Conclusions

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Motivation

• Knowing the bottleneck bandwidth of a route
  benefits
• Applications in general
• Developers of network protocols and applications
• Network clients
• Mobile computing
• Congestion control
• Multicast routing trees

4
Metrics

• Bottleneck Bandwidth ? ideal bandwidth of the
  lowest bandwidth link on that route between two
  hosts. It is not affected by other traffic.
• Available Bandwidth ? maximum bandwidth at which
  a host can transmit at a given point in time
  along that route. It is limited by other traffic
  along that route.

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Current Techniques

• Use throughput to approximate bandwidth
• throughput amount of data a transport protocol
  can transfer per unit of time
• Other metrics may have significant effect on TCP
  throughput, while not affecting bandwidth
• An applications throughput to a host implies
  nothing about other transfers, even from the same
  application to the same host

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Current Techniques

• TCPs technique
• Measures the bottleneck routers buffer size too
• Wastes network resources by forcing a dropped
  packet and filling the routers buffers
• Has to increase its sending rate slowly, or else
  it will overshoot the real bandwidth and cause
  massive packet loss

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Current Techniques

• pathchar
• Measures bandwidth of every link accurately
• Requires special software on only one host
• Slow
• Can consume significant amounts of network
  bandwidth

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Packet Pair

• Measures true bandwidth of network
• Does not cause packet loss
• Does not require many packet roundtrips to work
• Does not send massive amounts of data

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Packet Pair

• Not statistically robust kernel density
  estimator
• Not scalable passive implementation
• Slow gradual packet pair implementation
• Not robust on all traffic Potential Bandwidth
  Filtering (PBF)
• Not flexible to bandwidth changes window
• Difficult to deploy Receiver Only Packet Pair
• Not studied under controlled conditions
  Simulation

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Bandwidth Measurement Algorithmspathchar

• Number of different packet sizes
• Total time where h number of hops, li round
  trip latency from sender to hop i, p number of
  packets sent per size (32)
• 10-hop Ethernet network,10ms avg latency ? 144s
• Avg bandwidth to probe a hop
• Total data transferred

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Bandwidth Measurement AlgorithmsPacket Pair

• Two packets queued next to each other at
  bottleneck link exit the link t seconds apart
• Assuming constant bottleneck separation
• If a packet queues in between

s2 size of second packet bbnl bottleneck
bandwidth
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Bandwidth Measurement AlgorithmsPacket Pair
Filtering (MBF)

• How to filter noise caused by time compressed and
  extended packets?
• Use mean or median of samples No!
• Use histogram to find point of greatest density
• Kernel density estimator algorithm
• gives greater weight to samples closer to the
  point at which we want to estimate the density
• Simple and fast to compute
• Makes no assumption about distribution it
  operates on

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Bandwidth Measurement AlgorithmsReceiver and
Sender Based PP

• RBPP t is measured at the receiver
• SBPP uses round trip time
• Filtering techniques can be used to reject
  incorrect estimates
• RBPP is more accurate but harder to deploy
• ROPP sacrifices a little accuracy for ease of
  deployment

ai arrival time of packet i
ri arrival time of ACK of packet i
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Bandwidth Measurement AlgorithmsTimeliness
versus Accuracy

• PP usually implemented to run over a fixed number
  of packets before providing estimate
• Solution Calculate bandwidth gradually
• Converges to correct bandwidth within 3 packets
• Problem slow to detect bandwidth change
• Solution use packet window (size w) BUT, may
  reduce stability

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Potential Bandwidth Filtering

• Potential Bandwidth Problem PP cannot measure a
  higher bandwidth than that at which the sender
  sends
• PBF ? correlate the potential bandwidth and
  measured bandwidth of a sample in deciding how to
  filter

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Simulations
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Simulations
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Simulations
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Simulations