pathChirp

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pathChirp STAB Measuring Available Bandwidth
and Locating Bottlenecks in Packet Networks

• Vinay Ribeiro
• Rolf Riedi, Richard Baraniuk
• Rice University
• spin.rice.edu

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Packet Networks
link

• Data transmitted as packets
• Routers forward packets until destination
• Routers buffer packets in queues
• Link bandwidth maximum data transmission rate
  (bits/sec)

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Network Expansion
NSFNET 1993
ARPANET 1969

• Grown in size and importance
• Crucial for commerce, government, research,

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Study Network Properties

• Properties
• connectivity between routers
• bandwidth used on different links
• queuing delays
• statistical properties of packet arrivals

• Improve network performance
• Network design
• Use bandwidth resources efficiently
• Reduce delays
• Assist network-aware applications

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Obtaining Network Information is Hard
Difficulties faced by network user

• Different parts of Internet owned by different
  organizations
• Information sharing difficult
• Commerical interests/trade secrets
• Privacy
• Direct measurement
• Router performance affected with too much
  measurement
• Tapping links, extra infrastructure, expensive
• Sheer volume of information
• Cannot measure everything

Difficulties faced by network administrator
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Edge-Based Probing

• Inject probe packets into network
• Infer internal properties from packet delay

End-to-end packet delay speed of light
propagation queuing delay
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Probing Uncertainty Principle

• Large volume of probe packets
• Accurate inference of network properties
• Inefficient use of precious bandwidth resources
• Small volume of probe packets
• Less accurate inference
• Efficient use of resources
• Balance tradeoff in accuracy vs. efficiency

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Available Bandwidth

• Link available bandwidth unused bandwidth on a
  link
• Path available bandwidth smallest available
  bandwidth of all links of a path
• Available bandwidth is time-varying
• Goal end-to-end probing to estimate path
  available bandwidth

Link bandwidth
100Mbps Bandwidth used to transmit packets
30Mbps Link available bandwidth
70Mbps
Example
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Applications

• Server selection

• Route selection (e.g. BGP, overlay networks)

• Service verification

• Tuning transport protocols

• Early warning of meltdown

• UDP-storm attack detection

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Probing Tool Requirements

• Fast, real-time estimate
• Accurate
• Efficient, introduce light probing load

• No topology assumptions (e.g. link bandwidths)

• No topology assumptions (e.g. link bandwidths)

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Self-Induced Congestion
Probing bit rate gt available bandwidth ? delay
increases
(queues start filling
up) Probing bit rate lt available bandwidth ? no
delay increase
(queues do not fill up)

• Advantages
• No topology information required
• Transition point gives estimate of available
  bandwidth

probe packets
low probing rate
time
high probing rate
time
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Chirp Packet Trains
(bits/sec)

• Exponentially decrease packet spacing within
  packet train
• Simultaneously probe at wide range of probing
  rates
• Efficient few packets

Example Chirp of 25 packets with ? 1.2 has
probing range 1--100Mbps
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Available Bandwidth estimation with pathChirp

• Segment delay profile into increasing/decreasing
  regions
• Apply principle of self-induced congestion to
  each region
• Average over different regions for per-chirp
  estimate
• Final estimate moving-average of per-chirp
  estimates

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Gigabit Testbed Experiment
Mbps
time (seconds)

• CAIDA/CalNGI bandwidth estimation lab
• Vary available bandwidth using cross-traffic
  generator
• pathChirp tracks available bandwidth well

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Thin Links

• Thin link link with less available bandwidth
  than all preceding links
• Sub-path available bandwidth A1,m smallest
  available bandwidth among first m links
• Goal use end-to-end probing to locate thin links
  in space and track changes in location over time

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Applications

• Science where does congestion occur and why?
• Network aware application
• Route around problem spots in Internet
• Network monitoring/troubleshooting
• Locating hot spots

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Estimating Sub-Path Available Bandwidth A1,m
1 2 m

• Replace each packet by two packets Big packet
  size P,
• 
  small packet size p
• Key Probing rate decreases by p/(pP) at link m
• Self-induced congestion only up to link m
• Small packets carry timing information to
  receiver

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Tight Link Localization with STAB

• Thin links links at which A1,m decreases
• Last thin link has least available bandwidth
  among all links
• Implemented in Spatio-Temporal Available
  Bandwidth estimator (STAB)

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Simulation
topology

• STAB tracks thin links well

Actual
Sub-path available Bandwidth A1,m (Mbps)
Probability that different links are thin links
Link number m
time (sec)
t180 sec
Estimated
Sub-path available Bandwidth A1,m (Mbps)
t360 sec
Link number m
time (sec)
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Internet Experiment

• Locate thin links on two paths simultaneously
• Estimated thin link locations are consistent for
  two paths

UIUC?Rice
Probability that different links are thin links
UWisc?Rice
UIUC?Rice
UWisc?Rice
Router data supports STAB results

Sub-path available Bandwidth A1,m (Mbps)
Sub-path available Bandwidth A1,m (Mbps)
time
Link number m
Link number m
time
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New Research Directions

• Spatio-temporal network tomography
• Wireless network probing

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Other Projects

• Synthesis of fractal data
• Alpha-Beta analysis of Internet data
• High-speed transport protocols

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Synthesis of Fractal Data
Classical Models (Markov/Poisson)
Bytes/time time series from an Internet link
Bytes per 600ms
Bytes per 60ms
Bytes per 6ms

• Internet data is fractal --- high variability if
  we zoom-in or zoom-out
• Fast synthesis using multifractal wavelet model
• Useful for simulations
• Code available at dsp.rice.edu
• People Matthew Crouse, Rolf Riedi, R. Baraniuk

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Alpha-Beta Analysis of Internet Data


Time series of bytes per 500ms
Alpha component Spiky Few connections
Beta component Gaussian Most connections

• Connection -- set of all packets with a unique
  source and destination
• Few connections (alpha) cause most of the
  spikes
• Implications for designing simulation topologies,
  queuing analysis, congestion control
• People Shriram Sarvotham, Rolf Riedi, Richard
  Baraniuk

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High-Speed Transport Protocols

• Transport protocols send at maximum data rate
  that does not congest network
• Current protocol (TCP-Reno) cannot utilize all
  the bandwidth on high-speed Giga-bit networks
• Existing solutions for high-speed networks too
  aggressive
• Negative impact on competing TCP-Reno connections
• Cannot deploy such solutions
• Hybrid protocol
• Utilizes bandwidth on high-speed networks
• Competes fairly with TCP-Reno connections
• People Ryan King, Rolf Riedi, Richard Baraniuk

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Conclusions

• pathChirp efficient probing tool to estimate
  path available bandwidth
• STAB probing tool to locate thin links in space
  and track changes in location over time
• Code (UNIX) Available for download at
  spin.rice.edu
• Other projects synthesis of fractal data
  (dsp.rice.edu), alpha-beta analysis, high-speed
  transport protocols