duke selfish mac layer misbehavior in wireless networks author: pradeep kyasanur and nitin h. vaidya...

DukeSelfish MAC Layer Misbehavior in Wireless

Networks

Author: Pradeep Kyasanur and Nitin H. VaidyaSome slides are borrowed from the author and

othersReviewed by Xuan Bao

Duke

www.themegallery.comwww.themegallery.com Company LogoCompany Logo

Index

Problem Definition1

Proposed Methods2

Modification3

Simulation Result4

Duke


Review of Details about DCF

Duke


Calculation of Contention Window (CW)

A host with data to transmit selects a random backoff counter from range [0, CW]

The backoff counter will decrease by one when the channel is idle for one time slot.

A host may access the channel when the counter reaches 0.

If a transmission is successful, CW is reset to the minimum value. Otherwise, CW is doubled, subject to the maximum value.

Duke


Opportunities of Misbehavior

Using analogy, the contention process is like throwing a dice and the competitor with the least points gets channel access.

Fairness is achieved because the loser in earlier contention will decrease their backoff counter and therefore has better chance to win the contention later.

Duke


Opportunities of Misbehavior

A selfish host can choose a small backoff counter by:

1 Choosing the backoff counter from a smaller region than [0, CW]

2 Do not increase CW after collision

Selfish Host

Backoff = rand[1,1]

Normal Host

Backoff = rand[0,CW]

Duke


The Reason Behind Misbehavior Opportunities

Senders, while participating in contention, maintain the CW value by themselves. Therefore, they are in fact both the regulator and participator in this game.

Duke


Conclusion on Definition of Misbehavior in This Paper

In this paper, selfish misbehavior only consider the sender’s behavior intending to obtain unfair share of channel access.

Does not consider high layer solutions.

Does not consider malicious attacks.

Duke


Index

Problem Definition1

Proposed Methods2

Methods3

Simulation Results4

Duke


Basic Frame

The receiver calculates and assign backoff counter to senders.

The receiver monitors the time interval between ACK and the next RTS. It identifies misbehavior based on the deviation between this interval and the assigned backoff counter.

Duke


Illustration Graph

DA

T

A

Sender S

Receiver R

CTS

AC

K(B

)

RTS

• R provides backoff B to S in ACK

• S uses B for backoff

• NewBackoff = f(backoff, ID, attempt)*CW

RTS

B

Duke


Penalty Scheme

Penalty is introduced in two time scale: per transmission and for the last w transmissions.

Duke


Penalty Scheme

For each transmission, a penalty proportional to the deviation D is added to the next backoff counter.

D = max (a*Bexp – Bact, 0) (misdiagnose)

For nodes keeps deviating more than a threshold T for the last W transmissions.

Further punishment such as refusal of accepting further packets.

Duke


Tradeoff Here

Choice of parameters as factor a, threshold T.

Misdiagnose may lead to unwanted performance degrading especially when refuse accepting further transmission or drop packets.

Duke


Index

Problem Definition1

Proposed Methods2

Modifications3

Simulation Result4

Duke


Problems and Consequence

Problem: Receiver may sense the channel under a

different status than the sender.

Consequence: Unjustified penalty to well behaved nodes.

Duke


Scenario

Classic Hidden Terminal Scenario

D

Y

S

M

KX

S reduces its backoff counter now, which will be considered as misbehavior later.

Duke


Solution

The receiver only classifies a slot to be busy when an overheard RTS/CTS has reserved the slot or a packet is being received.

Assumptions behind this: Deep carrier sensing. Carrier sensing range = 2 * Communication range

Duke


Index

Problem Definition1

Proposed Methods2

Modifications3

Simulation Results4

Duke

Throughput – no misbehavior

0

100

200

300

400

500

600

700

800

900

1000

1 2 4 8 16 32 64

Proposed Scheme

802.11

Number of sender nodes

Thr

ough

put

(Kbp

s \

node

)

Duke

Persistent Misbehavior -Diagnosis Accuracy

0

10

20

30

40

50

60

70

80

90

100

100959080706050403020100

Correct Diagnosis

Misdiagnosis

Percentage of Misbehavior (of misbehaving node)

Per

cent

age

Duke

Persistent Misbehavior- throughput

0

100

200

300

400

500

600

700

800

900

100959080706050403020100

802.11

Proposed Scheme

Percentage of Misbehavior

Thr

ough

put

(Kbp

s)

Avg. with proposed scheme

Avg. with 802.11

Duke

Click to edit company slogan .

duke selfish mac layer misbehavior in wireless networks author: pradeep kyasanur and nitin h. vaidya...

Documents

cw slide

company logo conclusion

backoff b

cw rts b slide

dcf slide

random backoff counter

assigned backoff counter

small backoff counter