© rabat anam mahmood ittc 1 resilience to jamming attacks rabat anam mahmood department of...

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© Rabat Anam MahmoodITTC

Resilience To Jamming Attacks

Rabat Anam Mahmood

Department of Electrical Engineering & Computer Science

[email protected]

1Jamming Attacks24 July 2008

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Jamming Attacks Outline

• Feasibility of Launching & Detecting Jamming Attacks in Wireless Networks

• Adaptive Radio Channel Allocation for Supporting Coexistence of 802.15.4 & 802.11b

• Defending Against Jamming Attacks in Wireless Local Area Networks

• References

24 July 2008 Jamming Attacks

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• References

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Jamming Attacks

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Jamming Attacks Wireless Networks

• Definitions and Characteristics

– A jammer is an entity who is purposefully trying to interfere with the physical transmission and reception of wireless communications

– A jammer continuously emits RF signals to fill a wireless channel so that legitimate traffic will be completely blocked

– Common characteristics for all jamming attacks is that their communications are not compliant with MAC protocols

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• Packet Send Ratio– The ratio of packets that are successfully sent out by

a legitimate traffic source compared to the number of packets it intends to send out at the MAC layer

• Reason– Channel busy– Transmission delayed– New packets dropped when buffer space is full– Packets that are too long in the buffer, timeout– N packets to send; M sent successfully– PSR = M/N


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• Packet Delivery Ratio– The ratio of packets that are successfully delivered

to a destination compared to the number of packets that have been sent out by the sender

• Reason– Destination may not be able to decode a received

packet due to interference


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• Jamming Attack Models

– Constant Jammer– Deceptive Jammer– Random Jammer– Reactive Jammer


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• Constant Jammer

– Continuously emits a radio signal– Sends out random bits to the channel– Does not follow any MAC layer etiquette– Does not wait for the channel to become idle


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• Deceptive Jammer

– Constantly injects regular packets to the channel– Normal nodes will be deceived by the packets– Normal nodes just check the preamble and remain

silent– Hence jammer can only send out preambles


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• Random Jammer

– Alternates between sleeping and jamming

– After jamming for tj units of time, it turns off its radio and enters the sleeping mode

– After sleeping for ts units of time it will wake up and resume jamming

– tj and ts may be random or fixed intervals taking energy conservation into consideration

– During wake up phase it can behave as a constant or a deceptive jammer


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• Reactive Jammer

– Not necessary to block the channel when nobody is communicating

– Jammer stays quiet when the channel is idle– Jammer starts transmitting a radio signal as soon as

it senses activity on the channel– Does not conserve energy because the jammer’s

radio must be continuously on in order to sense the channel

– However, it is harder to detect


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• Detecting Jamming Attacks

– Signal Strength– Carrier Sensing Time– Packet Delivery Ratio


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• References

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Radio Channel Allocation Coexistence of 802.15.4 and 802.11b

• Coexistence– Ability of one system to perform a task in a given

shared environment where other systems may or may not be using the same set of rules.

• Solution– Multiple radio channels for the coexistence of

802.15.4 LR WPAN and 802.11b WLAN


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• 802.11b has a radio transmission range of 100m• 802.15.4 has a radio transmission range of 10m• 802.11b gives radio interference to 802.15.4

system in a large area and from a long distance• Performance degradation of 802.15.4 caused by

the interference from 802.11b by 92% (a study shows)


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• IEEE 802.11b has 11 channels– Each channel has a frequency range of 22 MHz

• IEEE 802.15.4 has 16 channels– Each channel is 5 MHz apart– Each channel has a frequency range of 3 MHz

• Frequencies of each 802.11 channel overlaps with frequency ranges for four different 802.15.4 channels

• Channels 25 & 26 can be used where frequent interference of 802.11b is expected


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• Interference Detection

– Clear channel assessment or energy detection provided as RSSI (Received Signal Strength Indicator) services in 802.15.4.

– RSSI services called periodically or on demand when a sudden degradation of user throughput below a threshold is detected

– If RSSI confirms that the energy level on a current channel is above the threshold, channel interference is recognized


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• Group Formation

– Nodes under the effect of interference start broadcasting Group Formation messages to the immediate neighbors

– Due to interference nodes may or may not receive GF message

– Nodes in a group change the current radio channel to a new one from the switching table.

– Border nodes provide channel conversion for the group.


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• Tear Down

– Nodes in a group periodically check if the previous channel is clear of interference.

– If so, a tear down message is sent to all the nodes in a group and the group is torn down.


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• Interference size represents the number of nodes in interference

• Success rate is percentage value relative to without interference


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• The percentage value is the delay increase relative to the delay without interference

• Since packets are routed through the interference area, the delay is not increased much


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• Comparison between packet delays of AODV and AODV plus (adaptive scheme)

• Due to adaptive scheme, lower packet delay is attained


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• Conclusion

– Performance degradation by interference is mainly caused from changing routing path.

– The overhead for switching radio channels is very small

– Hence, by employing the adaptive scheme, routing does not need to find a new path when it hits into an interference area.


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• References

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Defend Against Jamming Attacks Wireless Local Area Networks

• Wireless Jamming Attacks– RTS Jamming– CTS Jamming

• Solution– Cumulative-Sum-based (CUSUM) Detection Method


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• RTS Jamming

– Jammer occupies channel by continuously sending RTS frames with large NAV to access point (AP)

– AP replies with CTS which can be heard by nearby nodes

– Neighbor nodes will keep silent for a period of time indicated by NAV

– Neighbor nodes can hardly occupy the channel to communicate with the AP


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• CTS Jamming

– Jammer sends CTS frames with spoofed ID which is as same as AP

– Jammer keeps AP unaware of this behavior by either using directional antenna or remaining far away from the AP

– Neighbor nodes will assume AP is busy receiving data from a hidden node and will remain silent

– Neighbor nodes will never get a chance to occupy the channel


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• Defending against RTS/CTS attacks

– Two separate data windows for RTS & CTS– Size of the window is fixed– Source ID information of the frame is recorded– Latest frame gets the smallest index– Different score given to each frame using a function– Smallest index gains the highest score


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• CUSUM Method

– Sequential Detection Change Point methodMean value of some variable under surveillance will change from negative to positive whenever a change occurs.


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• Channel is nearly fairly shared among nodes• Source ID distribution of CTS / RTS frames is

uniform• If a node constantly occupies the channel, the

uniform distribution in this period will change• CUSUM is applied to detect changes in CTS

window• When a change point is detected,

corresponding CTS frames are suspicious


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• Ct series CTS scores received sequentially

• In normal situation E(Ct)=c

• a is an upper bound of c i.e. a≥c

• ct=Ct-a negative value during normal operation

• ct=Ct-a positive value during attack

• CUSUM value exceeds the threshold N, jamming attack alarm launched


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• Conclusion– CUSUM can accurately detect RTS/CTS jamming

attacks with little computation and storage cost– Although these attacks cannot totally prevent other

nodes from communication, they can seriously degrade the network throughput

– These attacks have lower traffic rates than normal jamming attack and are more difficult to detect


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• References

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Jamming Attacks References

• http://www.winlab.rutgers.edu/~trappe/Papers/JamDetect_Mobihoc.pdf

• http://ieeexplore.ieee.org/iel5/10422/33099/01559004.pdf?arnumber=1559004

• http://www.springerlink.com/content/l2qp0215r1268p4t/fulltext.pdf


© rabat anam mahmood ittc 1 resilience to jamming attacks rabat anam mahmood department of...

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