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A Jamming-Resistant MAC Protocol for Single-Hop Wireless Networks

A Jamming-Resistant MAC Protocol for Single-Hop Wireless Networks. Baruch Awerbuch (JHU) Andrea W. Richa (ASU) Christian Scheideler ( Uni PB). Wireless jamming. blocking of the wireless channel due to interference, noise or collision at the receiver side. X. X. X. X.

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A Jamming-Resistant MAC Protocol for Single-Hop Wireless Networks

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  1. A Jamming-Resistant MAC Protocol for Single-Hop Wireless Networks Baruch Awerbuch (JHU) Andrea W. Richa (ASU) Christian Scheideler (Uni PB) Jamming-Resistant MAC Protocol

  2. Wireless jamming • blocking of the wireless channel due to interference, noise or collision at the receiver side X X X X wireless nodes Jamming-Resistant MAC Protocol

  3. Adversarial physical layer jamming • a jammer listens to the open medium and broadcasts in the same frequency band as the network • no special hardware required • can lead to significant disruption of communication at low cost for the jammer honest nodes jammer Jamming-Resistant MAC Protocol

  4. Single-hop wireless network • nreliable honest nodes and one jammer; all nodes within transmission range of each other and of the jammer jammer Jamming-Resistant MAC Protocol

  5. Wireless communication model • at each time step, a node may decide to transmit a packet (nodes continuously contend to send packets) • a node may transmit or sense the channel at any time step (half-duplex) • when sensing the channel a node v may • sense an idle channel • receive a packet • sense a busy channel v Jamming-Resistant MAC Protocol

  6. Adaptive adversary • knows protocol and entire history • nodes cannot distinguish between adversarial jamming or a message collision • i.e., a node senses a busy channel in both cases • (T,λ)-bounded adversary, 0 < λ < 1: in any time window of size w ≥ T, the adversary can jam ≤ λw time steps steps jammed by adversary other steps w 0 1 … Jamming-Resistant MAC Protocol

  7. Constant-competitive protocol • a protocol is called constant-competitive against a(T,λ)-bounded adversary if the nodes manage to perform successful transmission in at least a constant fraction of the non-jammed steps (w.h.p. or on expectation), for any sufficiently large number of steps successful transmissions steps jammed by adversary other steps (idle channel, message collisions) w 0 1 … Jamming-Resistant MAC Protocol

  8. Our main contribution • symmetric local-control MAC protocol that is constant-competitive against any (T,1-ε)-bounded adversary after Ω (T / ε) steps w.h.p., for any constant 0<ε<1and anyT. • energy efficient: • converges to bounded amount of energy consumption due to message transmissions by nodes under continuous adversarial jamming (ε=0) • fast recovery from any state ~ Jamming-Resistant MAC Protocol

  9. Pros and Cons Pros: • no prior knowledge of global parameters • nodes do not know ε • no IDs needed Cons: • nodes know common rough estimate γ=O(1/(log T + loglog n)) • allow for superpolynomial change in n and polynomial change in T over time • fair channel use is not guaranteed Jamming-Resistant MAC Protocol

  10. Further contributions Leader election protocol: • robust and efficient • all nodes agree on a leader in O(T/ε)steps w.h.p. Fair use of the wireless channel: • share the channel fairly among all nodes (some nodes may dominate transmission probabilities in our MAC protocol) • converges in O(n/ε)steps w.h.p. ~ Jamming-Resistant MAC Protocol

  11. Traditional defenses • spread spectrum: frequency hopping over a wide frequency band • hard for a jammer to detect the used frequency fast enough in order to jam it • Problem: commonly used wireless devices (e.g., 802.11) have relatively narrow frequency bands • random backoff: • adaptive adversary too powerful for MAC protocols based on random backoff or tournaments (including the standard MAC protocol of 802.11 [BKLNRT’08]) Jamming-Resistant MAC Protocol

  12. Further related work • MAC protocol in [GGN’06] would not be able to sustain constant-competitive ratio if adversary can jam more than ½ the time steps. • more general scenario (adversary can also introduce malicious messages) • nodes know n • not energy efficient • reliable broadcast in grid [KBKV’06] • eventually terminates • honest nodes consume energy at much higher rates than adversary Jamming-Resistant MAC Protocol

  13. Overview • Jamming • Model • Our contributions • Related work • MAC protocol • Basic Approach • MAC protocol • Fast recovery • Energy Efficiency • Leader Election & Fair Use of the Channel • Future work Jamming-Resistant MAC Protocol

  14. Simple idea • each node v sends a message at current time step with probability pv ≤ pmax, for constant 0 < pmax << 1.p = ∑ pv (cumulativeprobability) qidle=probability the channel is idleqsuccess=probability that only one node is transmitting (successful transmission) • Claim.qidle . p ≤qsuccess ≤(qidle . p)/ (1-pmax) if (number of times the channel is idle)=(number of successful transmissions)p = θ(1) ! (what we want!) ~ Jamming-Resistant MAC Protocol

  15. Basic approach • a node v adapts pv based only on steps when an idle channel or a successful message transmission are observed, ignoring all other steps (including all the blocked steps when the adversary transmits!)! time idle steps successful transmissions steps jammed by adversary steps where collision occurred but no jamming Jamming-Resistant MAC Protocol

  16. Basic approach • a node v adapts pv based only on steps when an idle channel or a successful message transmission are observed, ignoring all other steps (including all the blocked steps when the adversary transmits!)! time idle steps successful transmissions steps jammed by adversary steps where collision occurred but no jamming Jamming-Resistant MAC Protocol

  17. Naïve protocol Each time step: • Node vsends a message with probability pv . If v does not send a message then • if the wireless channel is idle then pv = (1+ γ) pv • if vreceived a message thenpv = pv /(1+ γ) (Recall thatγ = O(1/(log T + loglog n)).) Jamming-Resistant MAC Protocol

  18. Problems • Basic problem:Cumulative probability p could be too large. • all time steps blocked due to message collisions w.h.p. time idle steps successful transmissions steps jammed by adversary steps where collision occurred but no jamming Jamming-Resistant MAC Protocol

  19. Problems • Basic problem:Cumulative probability pcould be too large. • all time steps blocked due to message collisions w.h.p. time idle steps successful transmissions steps jammed by adversary steps where collision occurred but no jamming Jamming-Resistant MAC Protocol

  20. Problems • Basic problem:Cumulative probability p could be too large. • all time steps blocked due to message collisions w.h.p. • Idea: If more than T consecutive time stepswithout successful transmissions, then reduce probabilities, which results in fast recovery of p. • Problem: Nodes do not know T. How to learn a good time window threshold? • It turns out that additive-increase additive-decrease is the right strategy! Jamming-Resistant MAC Protocol

  21. MAC protocol • each node vmaintains • probability valuepv, • time window thresholdTv, and • countercv • Initially, Tv = cv = 1andpv = pmax (< 1/24). • synchronized time steps (for ease of explanation) • Intuition:wait for an entire time window (according to current estimate Tv) until you can increase Tv Jamming-Resistant MAC Protocol

  22. MAC protocol In each step: • node v sends a message with probability pv . If v decides not to send a message then • if v senses an idle channel, then pv= min{(1+γ)pv , pmax} • if vsuccessfully receives a message, then pv= pv /(1+ γ)and Tv= max{Tv - 1, 1} • cv= cv + 1. If cv> Tvthen • cv= 1 • ifvdidnot receive a messagesuccessfullyin thelast Tv steps thenpv= pv /(1+ γ)andTv= Tv +1 Jamming-Resistant MAC Protocol

  23. Example: Low value of p • pv = 1/n2, Tv = 3, cv = 1 Sensing Wireless Channel (Idle) v Jamming-Resistant MAC Protocol

  24. Example: Low value of p • pv = (1+ γ) /n2, Tv = 3, cv = 2 Sensing Wireless Channel (Idle) v Jamming-Resistant MAC Protocol

  25. Example: Low value of p pv = (1+ γ)2 /n2, Tv = 3, cv = 3 Sensing Wireless Channel (Idle) v TAMU'08, Andrea Richa Jamming-Resistant MAC Protocol 25

  26. Example: Low value of p • pv = (1+ γ) 3/n2, Tv = 3, cv = 4 Sensing Wireless Channel (Jammed) v • pv = (1+ γ) 2/n2, Tv = 4, cv =1 Jamming-Resistant MAC Protocol

  27. Example: Low value of p • ~ polylog (n) idlesteps later: • pv = c/n, Tv ≤ √T polylog (n) ~ Wireless Channel v Jamming-Resistant MAC Protocol

  28. Example: Large p • pv = 1/c, Tv = 2, cv = 1 Sending Wireless Channel v Message Jamming-Resistant MAC Protocol

  29. Example: Large p • pv = 1/c, Tv = 2, cv = 2 Sensing Wireless Channel (collision) v Jamming-Resistant MAC Protocol

  30. Example: Large p • pv = 1/c, Tv = 2, cv = 3 Sensing Wireless Channel (Jammed) v pv = 1/[c(1+ γ)], Tv = 3, cv = 1 Jamming-Resistant MAC Protocol

  31. Example: Large p • pv = 1/[c(1+ γ)], Tv = 3, cv = 1 Sending Wireless Channel v Message Jamming-Resistant MAC Protocol

  32. Example: Large p • pv = 1/[c(1+ γ)], Tv = 3, cv = 2 Sensing Wireless Channel (Collision) v Jamming-Resistant MAC Protocol

  33. Example: Large p • pv = 1/[c(1+ γ)], Tv = 3, cv = 3 Sensing Wireless Channel (Collision) v Jamming-Resistant MAC Protocol

  34. Example: Large p • pv = 1/[c(1+ γ)], Tv = 3, cv = 4 Sensing Wireless Channel (Collision) v • pv = 1/[c(1+ γ) 2], Tv = 4, cv = 1 Jamming-Resistant MAC Protocol

  35. MAC protocol In each step: • node v sends a message with probability pv . If v decides not to send a message then • if v senses an idle channel, then pv= min{(1+γ)pv , pmax} • if vsuccessfully receives a message, then pv= pv /(1+ γ)and Tv= max{Tv - 1, 1} • cv= cv + 1. If cv> Tvthen • cv= 1 • ifvdidnot receive a messagesuccessfullyin thelast Tv steps thenpv= pv /(1+ γ)andTv= Tv +1 Why only successful steps?? Jamming-Resistant MAC Protocol

  36. Counterexample SupposethatSv pvisverylow. Repeat indefinitely: Channel idle for one step Channel jammed for Tv steps Channel jammed for Tv-1 steps pv   no progress! Tv  Jamming-Resistant MAC Protocol

  37. Our results • Let N = max {T,n} • Theorem. The MAC protocol is constant-competitive under any (T,1-ε)-bounded adversary if the protocol is executed for Ω(log N max{T,log3N/(εγ2)} /ε) steps w.h.p., for any constant 0<ε<1and anyT. Jamming-Resistant MAC Protocol

  38. Proof sketch • Show competitiveness for time frames of F = θ((log N max{T,log3N/(εγ2)} /ε) many steps If we can show constant competitiveness for any such time frame of size F, the theorem follows • Use induction over the number of sufficiently large time frames seen so far. We subdivide each frame: I’ I f =θ(max{T,log3N/(εγ2)}) F = (log N / ε)  f Jamming-Resistant MAC Protocol

  39. Proof sketch • p > 1/(f2(1+γ)2√f) and Tv< √F, in each subframe I’ w.h.p. • p<12 and p>1/12 within subframe I’ with moderate probability (so that adaptive adversarial jamming not successful) • Constant throughput in I’ with moderate probability • Over a logarithmic number of subframes, constant throughput in frame I of size F w.h.p. Jamming-Resistant MAC Protocol

  40. Overview Jamming Model Our contributions Related work MAC protocol Basic Approach MAC protocol Fast recovery Energy Efficiency Leader Election & Fair Use of the Channel Future work TAMU'08, Andrea Richa Jamming-Resistant MAC Protocol 40

  41. Fast recovery • Our protocol quickly recovers from any (Tv,cv,,pv)-values. • Theorem. For any initial p0= ∑ pv and T0 = max Tv, it takes O([log(1+ γ) (1/ p0 )]/ε +T02) w.h.p. until the MAC protocol satisfies again p ≥ 1/(f2(1+γ)2√f) and Tv< √F for all v. Jamming-Resistant MAC Protocol

  42. Proving fast recovery: p • p0 < 1/(f2(1+γ)2√f) • we show that it takes roughly[log(1+ γ) (1/ p0 )]/εsteps to get down fromp0 to (p0)1/2; another[log(1+ γ) (1/ p0 )]/ (2ε) steps to get to(p0)1/4; …roughly at most 2[log(1+ γ) (1/ p0 )]/εuntil cumulative probability p ≥ 1/(f2(1+γ)2√f) Jamming-Resistant MAC Protocol

  43. Proving fast recovery: T • Once cumulative probability p ≥ 1/(f2(1+γ)2√f), count number of steps until Tv< √F for all v • repeated applications of similar inductive argument as MAC protocol’s, by repeatedly selecting appropriately geometric decreasing frame sizes(starting from 4 maxTv). Jamming-Resistant MAC Protocol

  44. Energy efficiency • Corollary. For any time frame of size F = Ω((log N max{T,log3N/(εγ2)} /ε), the total energy spent by all nodes together on sending out messages is bounded by O(F) whp. • Total amount of energy spent proportional to number of successful transmissions. Jamming-Resistant MAC Protocol

  45. Continuous jamming Moreover, under a more powerful adversary that can perform continuous jamming (afterΩ(T)steps): Lemma. The total energy consumption (sending out messages) during an entire continuous jamming attack is O(√T), independent of the length of the attack. Exhaust adversary’s energy resources ~ ~ TAMU'08, Andrea Richa Jamming-Resistant MAC Protocol 45

  46. Proving Lemma • First we show that the total energy consumption is O(p0 . T0/ γ + log N) whp, where p0=∑ pv and T0= maxTv at the start of the attack • compute expected number transmissions out of each node given that pv decreases by 1/(1+ γ) every T0 +1, then T0 +2 , then T0 +3, … number of steps under continuous jamming • sum up expected values over all nodes and use Chernoff bounds • Note that for an attack starting after Ω(T)steps, p0 =O(1) and T0=O(√F)= O(√T), whp. ~ ~ Jamming-Resistant MAC Protocol

  47. Overview Jamming Model Our contributions Related work MAC protocol Basic Approach MAC protocol Fast recovery Energy Efficiency Leader Election & Fair Use of the Channel Future work TAMU'08, Andrea Richa Jamming-Resistant MAC Protocol 47

  48. Leader election ~ • all nodes agree on a leader in O(T/ε)steps w.h.p. • robust and efficient • tournament based leader election protocols are not robust against adversarial jamming • Basic Idea: • each node will keep a counter for the number of successful transmissions received so far; • the node that receives the least amount of successful transmissions (and hence sent the largest amount of successful transmissions) will become the leader node Jamming-Resistant MAC Protocol

  49. Leader election: Basic Ideas • In addition to the triples (pv,Tv,cv) each node vmaintains • counter sv for estimate on total number of successful transmissions so far • one of the states {unknown, leader, follower} • Initially, all nodes are at unknown. Jamming-Resistant MAC Protocol

  50. Leader election protocol • Modify the MAC protocol slightly: … • if vsuccessfully receives a message, then pv= pv /(1+ γ)and Tv= max{Tv - 1, 1} if v is still in the state unknown, then v checks if: (1) sv≥ sw, then v becomes a follower (2) sv< sw,then v becomes aleader vsetssv := max{sv, sw}+1 … Jamming-Resistant MAC Protocol

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