ARES: an Anti-jamming REinforcement System for 802.11 Networks

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ARES an Anti-jamming REinforcement System
for 802.11 Networks

• Konstantinos Pelechrinis, Ioannis Broustis,
• Srikanth V. Krishnamurthy, Christos Gkantsidis
• ACM CoNEXT 2009

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Launching DoS Attacks in WiFi networks is easy
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Launching DoS Attacks in WiFi networks is easy
Alice senses medium busy
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Launching DoS Attacks in WiFi networks is easy
Packet collisions
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Launching DoS Attacks in WiFi networks is easy

• Jammer can be
• Continuous
• Intermittent random or reactive

Xu et al MobiHoc 2005
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Launching DoS Attacks in WiFi networks is easy

• How to deal with jammers?
• Frequency hopping ??
• Two flavors (a) Reactive, (b) Proactive

• Frequency hopping is weak for current systems
  WiOpt 2009
• Only 4 jammers to block entire 5GHz spectrum

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Launching DoS Attacks in WiFi networks is easy
Can we alleviate jamming effects without relying
on frequency hopping?
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Our Contributions/Findings

• Fixed rates are often preferable in the presence
  of a jammer
• Rate adaptation converges slowly
• Clear Channel Assessment (CCA) tuning is
  important
• The transmitter can ignore jamming signals
• The receiver can latch on the desired signal more
  easily
• ARES A measurement driven anti-jamming system
  which utilizes rate and power control techniques.
• ARES fights jammer, instead of trying to avoid it
• Testbed evaluations show the potentials of ARES
• Up to 3x better performance

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Roadmap

• Introduction
• Rate Control
• Power Control
• System architecture
• Evaluation
• Conclusions

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Interaction between random jamming and rate
control
Jamming effects last beyond the jamming period
when rate control is used !
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Rate Control Fixed or Variable?

• In general, rate adaptation improves performance
  under benign condition.
• But, in the presence of an intermittent jammer
• The rate control algorithm might be slow to
  converge to optimum rate
• Remedy Fixed rate assignments increase
  immediately throughput
• But, performance depends on channel conditions

How to decide when to allow rate adaptation and
when not?
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Deciding when to perform rate adaptation

• With perfect knowledge of
• Application data rate Ra
• Jammers distribution
• Rate control algorithm used
• Link quality (e.g., PDR)
• Effectiveness of jammer (measured via the
  throughput sustained on the link)
• we can analytically decide between fixed rate and
  rate control.

• Average throughput over a jamming cycle .

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Fixed rate provides high throughput gains

• Throughput gains are indeed viable in practice
  with fixed rates under the presence of random
  jamming.

Corollary Use rate control only when the link is
very poor. E.g. for Ra54Mbps, rate adaptation
is preferred only if PDR is as low as 0.15 (for
sample rate)
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Practical algorithm for deciding when to rate
control

• However, perfect knowledge is not realistic
• Our Markovian Rate Control (MRC) module is
  inspired from the analysis but does not require
  knowledge of any of the parameters.

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MRC performs well in practice

• Parameter k controls the performance of MRC.
• MRC can be tuned to give performance close to the
  optimal.

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Roadmap

• Introduction
• Rate Control
• Power Control
• System architecture
• Evaluation
• Conclusions

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Power Control

• Rate control removes transient jamming effects.
• What about constant jamming effects?
• Power Control
• Power adaptation
• Clear Channel Assessment (CCA) tuning
• Power adaptation helps only when
• Transmitter is not in the jammers range.
• When low transmissions rates are used.
• Increasing CCA at the transceivers can restore
  the benign throughput with high probability.
• Care for avoiding starvation.

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Increasing power helps when transmission rate is
low

• Observation 1 Probability of accessing the
  medium does not depend on transmission power.
• Observation 2 Given that a packet is transmitted
• Power adaptation increases Signal / Jamming
  Interference Ratio.
• Improvements when low transmission rates are
  used.

Restricted solution. Ideal solution should be
agnostic to Jammers range Rate used
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Dealing with high power jammers

• In the presence of a high power jammer
• The transmitter needs to be able to ignore
  jamming signals.
• The receiver must be able to decode the
  legitimate packet.
• Tuning the transmission power increases the
  legitimate signal level at the receiver, but not
  very helpful when the jamming interference is
  also large enough.
• Observation 3 CCA threshold dictates both
  transmitting and receiving functionality
• Transmitter total energy at the transmitters
  antenna lt CCA ? idle medium
• Receiver signals with energy lt CCA ? noise
• Increasing the CCA threshold does NOT increase
  the SNR at the receiver.
• It helps the receiver latch on the legitimate
  signal.

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Side effects of power control

• Care needs to be taken for possible side effects
• Transmitter unintentionally become a jammer ?
  starve other nodes
• Mahtre et al Infocom 2007 P?CCA constant
• Receiver blindly increasing CCA ? legitimate
  signals regarded as noise
• Upper bound at CCA value for not ignoring signals
  of interest

Connectivity starts to be compromised ! !
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How to perform Power Control?

• Shadow fading variation ? Signal levels vary
  from their average value by ?dBm.
• RSSIij is the signal level at node j due to the
  transmission of node i (i,j T(transmitter),
  R(receiver) and J(jammer)).
• Heuristic for CCA on the link (CCAL)
• If max(RSSIJT, RSSIJR) min(RSSIRT, RSSITR) ?
• CCAL min(RSSIRT, RSSITR) ?
• If max(RSSIJT, RSSIJR) min(RSSIRT, RSSITR) 2?
• Link operates as in jamming free environment.
  

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ARES System Design

• ARES performs rate control and power control.
• Rate control uses the Markov Rate controller.
• Power control sets the CCA value based on the
  RSSIs and the value for the shadow fading
  variation ?.
• Both rate and power control are
  measurement-driven heuristics.

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Roadmap

• Problem motivation
• Our Contributions/Findings
• Background/Related Studies
• System Design
• Rate Control Measurements
• Power Control Measurements
• Evaluation
• Conclusions

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Evaluation Setup

• Experimental evaluation on our indoor wireless
  testbed.
• Hardware used
• Intel-2915 with ipw2200 driver/firmware (allows
  tuning CCA).
• EMP-8602 6G
• Ralink RT2860 (support 802.11n)
• Jammer implementation
• Utilize Intel cards
• CCA ? 0 dBm
• User space utility that sends broadcast packets
  back to back

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Effect of rate control on 802.11n

• Rate Control only
• Benchmark results using analytical assessments
• ARES Improves performance by up to 100

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Mobile Jammer

• The jammer (constant) moves to the vicinity of
  the legitimates nodes, stays there for k seconds
  and leaves.
• ARES utilizes power control module
• Increased CCA to overcome the presence of the
  jammer
• Rate adaptation module is not of much benefit in
  this scenario.
• ARES increases throughput by gt150

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Using rate control to avoid neighbor starvation

• ARES (MRC) improves neighbors AP throughput.
• Avoid transmissions at lower rates during the
  sleeping cycles.
• Neighbor APs and links have to wait less time to
  obtain the medium.
• Improved overall, networked setting performance
• With one neighbor AP (and one jammed) 23
  improvement
• Adding more APs reduces the benefits due to
  increased contention.

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Roadmap

• Problem motivation
• Our Contributions/Findings
• Background/Related Studies
• System Design
• Rate Control Measurements
• Power Control Measurements
• Evaluation
• Conclusions

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Conclusions

• Fixed rate assignments can be beneficial in
  jammed environments.
• Power level tuning helps only at low rates and
  low power jammers.
• Tuning the CCA threshold enables
• The transmitter to ignore jamming signals
• The receiver capture the desired packet(s)
• Evaluations of our measurement driven prototype
  system shows that rate and power control can
  efficiently fight against the jammer.
• Frequency hopping tries to avoid the jammer.

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• THANK YOU !!
• QUESTIONS?