a jamming-resistant mac protocol for single-hop wireless networks
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Jamming-Resistant MAC Protocol 1
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)
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Jamming-Resistant MAC Protocol 2
Wireless jamming
● blocking of the wireless channel due to interference, noise or collision at the receiver side
wireless nodes
XXXX
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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
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Jamming-Resistant MAC Protocol 4
Single-hop wireless network
● n reliable honest nodes and one jammer; all nodes within transmission range of each other and of the jammer
jammer
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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
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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
0 1 … w
steps jammed by adversary
other steps
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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
0 1 … w
other steps (idle channel, message collisions)
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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<1 and any T.
● 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
~
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Jamming-Resistant MAC Protocol 9
Pros and ConsPros:● 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
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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.
~
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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])
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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
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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
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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 (cumulative probability) 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!)
~
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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!)!
steps jammed by adversary
idle steps
successful transmissions
steps where collision occurred but no jamming
time
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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!)!
steps jammed by adversary
idle steps
successful transmissions
steps where collision occurred but no jamming
time
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Jamming-Resistant MAC Protocol 17
Naïve protocol
Each time step:
● Node v sends 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 v received a message then pv = pv /(1+ γ)
(Recall that γ = O(1/(log T + loglog n)). )
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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.
steps jammed by adversary
idle steps
successful transmissions
steps where collision occurred but no jamming
time
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Jamming-Resistant MAC Protocol 19
Problems
● Basic problem: Cumulative probability p could be too large. – all time steps blocked due to message collisions w.h.p.
steps jammed by adversary
idle steps
successful transmissions
steps where collision occurred but no jamming
time
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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 steps without 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!
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Jamming-Resistant MAC Protocol 21
MAC protocol● each node v maintains
– probability value pv ,
– time window threshold Tv , and
– counter cv
● Initially, Tv = cv = 1 and pv = 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
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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 v successfully receives a message, then pv = pv /(1+ γ) and Tv = max{Tv - 1, 1}
● cv = cv + 1. If cv > Tv then
– cv = 1
– if v did not receive a message successfully in the last Tv
steps then pv = pv /(1+ γ) and Tv = Tv +1
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Jamming-Resistant MAC Protocol 23
Example: Low value of p
● pv = 1/n2, Tv = 3, cv = 1
v Wireless Channel (Idle)Sensing
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Jamming-Resistant MAC Protocol 24
Example: Low value of p
● pv = (1+ γ) /n2, Tv = 3, cv = 2
v Wireless Channel (Idle)Sensing
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TAMU'08, Andrea Richa 25
Example: Low value of p
● pv = (1+ γ)2 /n2, Tv = 3, cv = 3
v Wireless Channel (Idle)Sensing
25Jamming-Resistant MAC Protocol
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Jamming-Resistant MAC Protocol 26
Example: Low value of p
● pv = (1+ γ) 3/n2, Tv = 3, cv = 4
v
pv = (1+ γ) 2/n2, Tv = 4, cv =1
Wireless Channel (Jammed)Sensing
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Jamming-Resistant MAC Protocol 27
Example: Low value of p
● ~ polylog (n) idle steps later:– pv = c/n, Tv ≤ √T polylog (n)
v Wireless Channel
~
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Jamming-Resistant MAC Protocol 28
Example: Large p
● pv = 1/c, Tv = 2, cv = 1
v Wireless ChannelSending
Message
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Jamming-Resistant MAC Protocol 29
Example: Large p
● pv = 1/c, Tv = 2, cv = 2
v Wireless Channel (collision)Sensing
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Jamming-Resistant MAC Protocol 30
Example: Large p
● pv = 1/c, Tv = 2, cv = 3
v Wireless Channel (Jammed)Sensing
pv = 1/[c(1+ γ)], Tv = 3, cv = 1
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Jamming-Resistant MAC Protocol 31
Example: Large p
● pv = 1/[c(1+ γ)], Tv = 3, cv = 1
v Wireless ChannelSending
Message
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Jamming-Resistant MAC Protocol 32
Example: Large p
● pv = 1/[c(1+ γ)], Tv = 3, cv = 2
v Wireless Channel (Collision)Sensing
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Jamming-Resistant MAC Protocol 33
Example: Large p
● pv = 1/[c(1+ γ)], Tv = 3, cv = 3
v Wireless Channel (Collision)Sensing
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Jamming-Resistant MAC Protocol 34
Example: Large p
● pv = 1/[c(1+ γ)], Tv = 3, cv = 4
v Wireless Channel (Collision)Sensing
pv = 1/[c(1+ γ) 2], Tv = 4, cv = 1
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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 v successfully receives a message, then pv = pv /(1+ γ) and Tv = max{Tv - 1, 1}
● cv = cv + 1. If cv > Tv then
– cv = 1
– if v did not receive a message successfully in the last Tv
steps then pv = pv /(1+ γ) and Tv = Tv +1
Why only successful steps??
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Counterexample
Suppose that v pv is very low.
Repeat indefinitely:
Jamming-Resistant MAC Protocol 36
Channel jammed for Tv steps
Channel idle for one step
pv
Tv
Channel jammed for Tv-1 steps
no progress!
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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,log3 N/(ε γ2)} / ε) steps w.h.p., for any constant 0<ε<1 and any T.
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Jamming-Resistant MAC Protocol 38
Proof sketch● Show competitiveness for time frames of F =
θ((log N max{T,log3 N/(ε γ2)} / 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:
II’
f = θ(max{T,log3 N/(ε γ2)})
F = (log N / ε) f
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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.
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TAMU'08, Andrea Richa 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
40Jamming-Resistant MAC Protocol
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Jamming-Resistant MAC Protocol 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.
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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 )]/ ε steps to get down from p0 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 )]/ ε until cumulative probability p ≥ 1/(f2(1+γ)2√f)
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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 max Tv ).
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Energy efficiency
● Corollary. For any time frame of size F = Ω((log N max{T,log3 N/(ε γ2)} / 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.
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TAMU'08, Andrea Richa 45
Continuous jamming
● Moreover, under a more powerful adversary that can perform continuous jamming (after Ω(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
~
~
45Jamming-Resistant MAC Protocol
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Proving Lemma
● First we show that the total energy consumption is O(p0 . T0/ γ + log N) whp, where p0=∑ pv and T0 = max Tv 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. ~
~
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TAMU'08, Andrea Richa 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
47Jamming-Resistant MAC Protocol
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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
~
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Jamming-Resistant MAC Protocol 49
Leader election: Basic Ideas
● In addition to the triples (pv,Tv ,cv) each node v maintains – 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.
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Jamming-Resistant MAC Protocol 50
Leader election protocol
● Modify the MAC protocol slightly: …
– if v successfully 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 a leader
v sets sv := max{sv, sw}+1
…
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Jamming-Resistant MAC Protocol 51
Example: Leader election
v
sv = 0 sw = 0
Message, sv = 0
all other nodes w
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Example: Leader election
v
sv = 0 sw = 0
Message, sv = 0
all other nodes w
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Jamming-Resistant MAC Protocol 53
Example: Leader election
v
sv = 0
all other nodes w
sw = 0
Message, sv = 0
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Example: Leader election
v
sv = 0
w
sw = 0
sw ≥ sv, then w becomes a “follower” and sw = max{ sw , sv } + 1 = 1
sw = 1
follower
Message, sv = 0
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Example: Leader election
v
sv = 0
w
sw = k+1
Message, sw = k+1
After v continues successfully transmitting for k more steps. Now the first node w ≠ v is transmitting a message to v, with sw = k+1.
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Example: Leader election
v
sv = 0
w
sw = k+1
Message, sw = k+1
After v continues successfully transmitting for k more steps. Now the first node w ≠ v is transmitting a message to v, with sw = k+1.
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Example: Leader election
v
sv = 0
w
sw = k+1
Message, sw = k+1
After v continues successfully transmitting for k more steps, until first node w ≠ v successfully transmits a message. Now sw = k+1,
and sv = 0.sv < sw, then v becomes a “leader”
leader
sv = k+2
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Our results: Leader election
● Let N = max {T,n}
● Theorem. Within O(log N max{T,log3 N/(ε γ2)} / ε) many steps, the leader election protocol reaches a state in which there is exactly one leader and the other nodes are followers, w.h.p.
● Proof: It takes O(log N max{T,log3 N/(ε γ2)} / ε) until two distinct nodes transmit a message.
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Fairness
● share the channel fairly among nodes– MAC protocol can be rather unfair
– some probabilities may eventually dominate others
● simple counter-based mechanism (as in the leader election protocol) would fail here…
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Fairness: Basic ideas
● each node v also maintains an additional counter mv of the different nodes which had successful transmissions so far
● the protocol aims at setting pv = pmax /2mv, which will eventually converge to pv = pmax /2n (= θ(1/n))
● converges in O(n/ε) steps w.h.p.
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Future work
● Can the MAC protocol be extended to multihop wireless networks?
● How can we adapt to node join and leave operations?● Can the MAC protocol be modified so that no rough
bound on n and T are required?● stochastic/oblivious jammers: Simpler to handle?
E.g., a constant gamma seems to work fine here.● Other applications of the MAC protocol?
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Questions?