mac protocols and security in ad hoc and sensor networks

MAC Protocols and Security in Ad hoc and Sensor Networks

– A power control MAC A power control MAC protocol allows nodes to vary transmit power level on a protocol allows nodes to vary transmit power level on a

per-packet basisper-packet basis

– Earlier work has used different power levels for RTS-CTS and DATA-ACK, Earlier work has used different power levels for RTS-CTS and DATA-ACK,

specifically, maximum transmit power is used for RTS-CTS and minimum specifically, maximum transmit power is used for RTS-CTS and minimum

required transmit power is used for DATA-ACK transmissionsrequired transmit power is used for DATA-ACK transmissions

– These protocols may increase collisions, degrade network throughput and result These protocols may increase collisions, degrade network throughput and result

in higher energy consumption than when using IEEE 802.11 without power in higher energy consumption than when using IEEE 802.11 without power

controlcontrol

– Power saving mechanismsPower saving mechanisms allow nodes to enter a allow nodes to enter a doze statedoze state by powering off its by powering off its

wireless network interface whenever possiblewireless network interface whenever possible

– Power control schemesPower control schemes vary transmit power to reduce energy consumption vary transmit power to reduce energy consumption

A Power Control MAC (PCM) Protocol for Ad hoc Networks[Jung+ 2002]

IEEE 802.11 MAC ProtocolIEEE 802.11 MAC Protocol

– Specifies two MAC protocols:Specifies two MAC protocols:

Point Coordination Function (PCF) Point Coordination Function (PCF) centralized centralized

Distributed Coordination Function (DCF) Distributed Coordination Function (DCF) distributeddistributed

Transmission range:Transmission range:

When a node is in transmission range of a sender node, it can receive andWhen a node is in transmission range of a sender node, it can receive andcorrectly decode packets from sender node.correctly decode packets from sender node.

Carrier Sensing Range:Carrier Sensing Range:

Nodes in carrier sensing range can sense the sender’s transmission. It is generally Nodes in carrier sensing range can sense the sender’s transmission. It is generally

larger than transmission range. Both carrier sensing range and transmission rangelarger than transmission range. Both carrier sensing range and transmission range

Depends on the transmit power level.Depends on the transmit power level.

Power Control MAC (PCM)


Carrier Sensing Zone:Carrier Sensing Zone:

Nodes can sense the signal, but cannot decode it correctly. The carrier sensing zone Nodes can sense the signal, but cannot decode it correctly. The carrier sensing zone

does not include transmission rangedoes not include transmission range


[Figure adapted from Jung+ 2002]


– DCF in IEEE 802.11 is based on CSMA/CS (Carrier Sense Multiple Access with DCF in IEEE 802.11 is based on CSMA/CS (Carrier Sense Multiple Access with

Collision Avoidance)Collision Avoidance)

– Each node in IEEE 802.11 maintains a NAV (Network Allocation Vector) that Each node in IEEE 802.11 maintains a NAV (Network Allocation Vector) that

indicates the remaining time of the on-going transmission sessionsindicates the remaining time of the on-going transmission sessions

– Carrier sensing is performed using physical carrier sensing (by air interface) and Carrier sensing is performed using physical carrier sensing (by air interface) and

virtual carrier sensing (uses the duration of the packet transmission that is virtual carrier sensing (uses the duration of the packet transmission that is

included in the header of RTS, CTS and DATA frames)included in the header of RTS, CTS and DATA frames)

– Using the duration information in RTS, CTS and DATA packets, nodes update Using the duration information in RTS, CTS and DATA packets, nodes update

their NAVs whenever they receive a packettheir NAVs whenever they receive a packet

– The channel is considered busy if either physical or virtual carrier sensing The channel is considered busy if either physical or virtual carrier sensing

indicates that channel is busyindicates that channel is busy

– Figure 2 shows how nodes in transmission range and the carrier sensing zone Figure 2 shows how nodes in transmission range and the carrier sensing zone

adjust their NAVs during RTS-CTS-DATA-ACK transmission adjust their NAVs during RTS-CTS-DATA-ACK transmission



– IFS is the time interval between frames and IEEE 802.11 defines four IFSs which IFS is the time interval between frames and IEEE 802.11 defines four IFSs which

provide priority levels for accessing the channel provide priority levels for accessing the channel

SIFS (short interframe space)SIFS (short interframe space)

PIFS (Point Coordination Function interframe space)PIFS (Point Coordination Function interframe space)

DIFS (Distributed Coordination Function interframe space)DIFS (Distributed Coordination Function interframe space)

EIFS (extended interframe space)EIFS (extended interframe space)

– SIFS is the shortest and is used after RTS, CTS, and DATA frames to give the SIFS is the shortest and is used after RTS, CTS, and DATA frames to give the

highest priority to CTS, DATA and ACK respectivelyhighest priority to CTS, DATA and ACK respectively

– In DCF, when the channel is idle, a node waits for DIFS duration before transmittingIn DCF, when the channel is idle, a node waits for DIFS duration before transmitting

– Nodes in the transmission range correctly set their NAVs when receiving RTS/CTSNodes in the transmission range correctly set their NAVs when receiving RTS/CTS

– Since nodes in carrier sensing zone cannot decode the packet, they do not know Since nodes in carrier sensing zone cannot decode the packet, they do not know

the duration of the packet transmission. So, they set their NAVs for the EIFS the duration of the packet transmission. So, they set their NAVs for the EIFS

duration to avoid collision with the ACK reception at the source nodeduration to avoid collision with the ACK reception at the source node



– The intuition behind EIFS is to provide enough time for a source node to receive the The intuition behind EIFS is to provide enough time for a source node to receive the

ACK frame, meaning that duration of EIFS is longer than that of ACK transmissionACK frame, meaning that duration of EIFS is longer than that of ACK transmission

– In PCM, nodes in the carrier sensing zone use EIFS whenever they can sense the In PCM, nodes in the carrier sensing zone use EIFS whenever they can sense the

signal but cannot decode itsignal but cannot decode it

– IEEE 802.11 does not completely prevent collisions due to the IEEE 802.11 does not completely prevent collisions due to the hidden terminalhidden terminal

problem (nodes in the receiver’s carrier sensing zone, but not in the sender’s carrier problem (nodes in the receiver’s carrier sensing zone, but not in the sender’s carrier

sensing zone or transmission range, can cause a collision with the reception of a sensing zone or transmission range, can cause a collision with the reception of a

DATA packet at the receiverDATA packet at the receiver

– In Figure 3, suppose node C transmits packet to node DIn Figure 3, suppose node C transmits packet to node D

– When C and D transmit an RTS and CTS respectively, A and F set their NAVs for When C and D transmit an RTS and CTS respectively, A and F set their NAVs for

EIFS durationEIFS duration

– During C’s data transmission, A defers its transmission due to sensing C’s During C’s data transmission, A defers its transmission due to sensing C’s

transmission. However, since node F does not sense any signal during C’s transmission. However, since node F does not sense any signal during C’s

transmission, it considers channel to be idle (F is in D’s carrier sensing zone, but not transmission, it considers channel to be idle (F is in D’s carrier sensing zone, but not

in D’s)in D’s)





D’s carrier sensing rangeC’s carrier sensing range


– When F starts a new transmission, it can cause a collision with the reception of When F starts a new transmission, it can cause a collision with the reception of

DATA at DDATA at D

– Since F is outside of D’s transmission range, D may be outside of F’s transmission Since F is outside of D’s transmission range, D may be outside of F’s transmission

range; however, since F is in D’s carrier sensing zone, F can provide interference at range; however, since F is in D’s carrier sensing zone, F can provide interference at

node D to cause collision with DATA being received at Dnode D to cause collision with DATA being received at D


BASIC Power Control ProtocolBASIC Power Control Protocol

– Power control can reduce energy consumptionPower control can reduce energy consumption

– Power control may bring different transmit power levels at different hosts, creating Power control may bring different transmit power levels at different hosts, creating

an asymmetric scenarios where a node A can reach node B, but node B cannot an asymmetric scenarios where a node A can reach node B, but node B cannot

reach node A and collisions may also increase a resultreach node A and collisions may also increase a result

– In Figure 4, suppose nodes A and B use lower power level than nodes C and DIn Figure 4, suppose nodes A and B use lower power level than nodes C and D

– When A is transmitting to B, C and D may not sense the transmissionWhen A is transmitting to B, C and D may not sense the transmission

– When C and D transmit to each other using higher power, their transmission may When C and D transmit to each other using higher power, their transmission may

collide with the on-going transmission from A to Bcollide with the on-going transmission from A to B




– As a solution to this problem, RTS-CTS are transmitted at the highest possible As a solution to this problem, RTS-CTS are transmitted at the highest possible

power level but DATA and ACK at the minimum power level necessary to power level but DATA and ACK at the minimum power level necessary to

communicatecommunicate

– In Figure 5, nodes A and B send RTS and CTS respectively with highest power In Figure 5, nodes A and B send RTS and CTS respectively with highest power

level such that node C receives the CTS and defers its transmissionlevel such that node C receives the CTS and defers its transmission

– By using a lower power level for DATA and ACK packets, nodes can save energyBy using a lower power level for DATA and ACK packets, nodes can save energy




– In the BASIC scheme, RTS-CTS handshake is used to decide the transmission In the BASIC scheme, RTS-CTS handshake is used to decide the transmission

power for subsequent DATA and ACK packets which can be achieved in two power for subsequent DATA and ACK packets which can be achieved in two

different waysdifferent ways

Suppose node A wants to send a packet to node B. Node A transmit RTS at Suppose node A wants to send a packet to node B. Node A transmit RTS at

power level power level ppmaxmax (maximum possible). When B receives the RTS from A with (maximum possible). When B receives the RTS from A with

signal level signal level ppr,r, B calculates the minimum necessary transmission power level, B calculates the minimum necessary transmission power level,

ppdesireddesired. For the DATA packet based on received power level, . For the DATA packet based on received power level, pprr, transmitted , transmitted

power level, power level, ppmaxmax, and noise level at the receiver B. Node B specifies , and noise level at the receiver B. Node B specifies ppdesired desired in in

its CTS to node A. After receiving CTS, node A sends DATA using power level its CTS to node A. After receiving CTS, node A sends DATA using power level

ppdesired.desired.

When a destination node receives an RTS, it responds by sending a CTS (at When a destination node receives an RTS, it responds by sending a CTS (at

power level power level ppmaxmax). When source node receives CTS, it calculates ). When source node receives CTS, it calculates ppdesireddesired based based

on received power level, on received power level, pprr, and transmitted power level (, and transmitted power level (ppmaxmax) as) as

PPdesired desired = = (p(pmaxmax / / pprr) x Rx) x Rxthreshthresh x c x c

where where RxRxthreshthresh is minimum necessary received signal strength and c is constant is minimum necessary received signal strength and c is constant



– The second alternative makes two assumptions:The second alternative makes two assumptions:

Signal attenuation between source and destination nodes is assumed to be the Signal attenuation between source and destination nodes is assumed to be the

same in both directionssame in both directions

Noise level at the receiver is assumed to be below some predefined threshold Noise level at the receiver is assumed to be below some predefined threshold

Deficiency of the BASIC ProtocolDeficiency of the BASIC Protocol

– In Figure 6, suppose node D wants to transmit to node EIn Figure 6, suppose node D wants to transmit to node E

– When nodes D and E transmits RTS and CTS respectively, B and C receives RTS When nodes D and E transmits RTS and CTS respectively, B and C receives RTS

and F and G receives CTS, therefore, these nodes defer their transmissionsand F and G receives CTS, therefore, these nodes defer their transmissions

– Since node A is in carrier sensing zone of node D, it sets its NAV for EIFS durationSince node A is in carrier sensing zone of node D, it sets its NAV for EIFS duration

– Similarly node H sets its NAV for EIFS duration when it senses transmission from ESimilarly node H sets its NAV for EIFS duration when it senses transmission from E

– When source and destination decide to reduce the transmit power for DATA-ACK, When source and destination decide to reduce the transmit power for DATA-ACK,

not only transmission range for DATA-ACK but also carrier sensing zone is also not only transmission range for DATA-ACK but also carrier sensing zone is also

smaller than RTS-CTS smaller than RTS-CTS


Deficiency of the BASIC ProtocolDeficiency of the BASIC Protocol

– Thus, only C and F correctly Thus, only C and F correctly

receives DATA and ACK packetsreceives DATA and ACK packets

– Since nodes A and H cannot Since nodes A and H cannot

sense the transmissions, they sense the transmissions, they

consider channel is idle and start consider channel is idle and start

transmitting at high power level transmitting at high power level

which will cause collision with the which will cause collision with the

ACK packet at D and DATA packet ACK packet at D and DATA packet

at Eat E

– This results in throughput This results in throughput

degradation and higher energy degradation and higher energy

consumption (due to consumption (due to

retransmissions)retransmissions)



Proposed Power Control MAC ProtocolProposed Power Control MAC Protocol

– Proposed Power Control MAC (PCM) is similar to BASIC scheme such that it uses Proposed Power Control MAC (PCM) is similar to BASIC scheme such that it uses

power level, power level, ppmaxmax, for RTS-CTS and the minimum necessary transmit power for , for RTS-CTS and the minimum necessary transmit power for

DATA-ACK transmissionsDATA-ACK transmissions

– Procedure of PCM is as follows:Procedure of PCM is as follows:

1.1. Source and destination nodes transmit the RTS and CTS using Source and destination nodes transmit the RTS and CTS using ppmax.max. Nodes in Nodes in

the carrier sensing zone set their NAVs for EIFS durationthe carrier sensing zone set their NAVs for EIFS duration

2.2. The source may transmit DATA using a lower power level The source may transmit DATA using a lower power level

3.3. Source transmits DATA at level of Source transmits DATA at level of ppmaxmax, periodically, for enough time so that , periodically, for enough time so that

nodes in the carrier sensing zone can sense it and this would avoid collision nodes in the carrier sensing zone can sense it and this would avoid collision

with the ACK packetswith the ACK packets

4.4. The destination node transmits an ACK using the minimum required power to The destination node transmits an ACK using the minimum required power to

reach the source nodereach the source node

– Figure 7 presents how the transmit power level changes during the sequence of Figure 7 presents how the transmit power level changes during the sequence of

RTS-CTS-DATA-ACK transmission RTS-CTS-DATA-ACK transmission



Proposed Power Control MAC ProtocolProposed Power Control MAC Protocol

– The difference between PCM and BASIC scheme is that PCM periodically increases The difference between PCM and BASIC scheme is that PCM periodically increases

the transmit power to the transmit power to ppmaxmax during the DATA packet transmission. Nodes that can during the DATA packet transmission. Nodes that can

interfere with the reception of ACK at the sender will periodically sense the channel interfere with the reception of ACK at the sender will periodically sense the channel

is busy and defer their own transmission. Since nodes reside in the carrier sensing is busy and defer their own transmission. Since nodes reside in the carrier sensing

zone defer for EIFS duration, the transmit power for DATA is increased once every zone defer for EIFS duration, the transmit power for DATA is increased once every

EIFS durationEIFS duration

– PCM solves the problem posed with BASIC scheme and can achieve throughput PCM solves the problem posed with BASIC scheme and can achieve throughput

comparable to 802.11 by using less energycomparable to 802.11 by using less energy

– PCM, like 802.11, does not prevent collisions completelyPCM, like 802.11, does not prevent collisions completely


– S- MAC S- MAC protocol designed specifically for sensor networks to reduce energy protocol designed specifically for sensor networks to reduce energy

consumption while achieving good scalability and collision avoidance by utilizing consumption while achieving good scalability and collision avoidance by utilizing

a combined scheduling and contention schemea combined scheduling and contention scheme

– The major sources of energy waste are:The major sources of energy waste are:

1.1. collisioncollision

2.2. overhearingoverhearing

3.3. control packet overheadcontrol packet overhead

4.4. idle listeningidle listening

– S-MAC reduce the waste of energy from all the sources mentioned in exchange S-MAC reduce the waste of energy from all the sources mentioned in exchange

of some reduction in both per-hop fairness and latencyof some reduction in both per-hop fairness and latency

An Energy-Efficient MAC Protocol for Wireless Sensor Networks (S-MAC)[Ye+ 2002]

– S- MAC S- MAC protocol consist of three major components:protocol consist of three major components:

1.1. periodic listen and sleepperiodic listen and sleep

2.2. collision and overhearing avoidancecollision and overhearing avoidance

3.3. Message passingMessage passing

– Contributions of S-MAC are:Contributions of S-MAC are:

The scheme of periodic listen and sleep helps in reducing energy The scheme of periodic listen and sleep helps in reducing energy

consumption by avoiding idle listening. The use of synchronization to consumption by avoiding idle listening. The use of synchronization to

form virtual clusters of nodes on the same sleep scheduleform virtual clusters of nodes on the same sleep schedule

In-channel signaling puts each node to sleep when its neighbor is In-channel signaling puts each node to sleep when its neighbor is

transmitting to another node (solves the overhearing problem and transmitting to another node (solves the overhearing problem and

does not require additional channel)does not require additional channel)

Message passing technique to reduce application-perceived latency Message passing technique to reduce application-perceived latency

and control overhead (per-node fragment level fairness is reduced)and control overhead (per-node fragment level fairness is reduced)

Evaluating an implementation of S-MAC over sensor-net specific Evaluating an implementation of S-MAC over sensor-net specific

hardwarehardware

S-MAC

– Security in wireless ad hoc networks is difficult for many reasons:Security in wireless ad hoc networks is difficult for many reasons:

Vulnerability of channelsVulnerability of channels

Vulnerability of nodesVulnerability of nodes

Absence of infrastructureAbsence of infrastructure

Dynamically changing topologyDynamically changing topology

– The problem is broad and there is no general solutionThe problem is broad and there is no general solution

– Different applications will have different security requirementsDifferent applications will have different security requirements

– Security aspects can be categorized into four groups:Security aspects can be categorized into four groups:

1.1. Trust and key managementTrust and key management

2.2. Secure routing and intrusion detectionSecure routing and intrusion detection

3.3. AvailabilityAvailability

4.4. Cryptographic protocolsCryptographic protocols

Security in Wireless Ad hoc Networks[Buttyan+ 2002]

References [Jung+ 2002] E.-S. Jung and N.H. Vaidya, A Power Control MAC Protocol for Ad hoc Networks,

Proceedings of ACM MOBICOM 2002, Atlanta, Georgia, September 23-28, 2002.

[Ye+ 2002] W. Yei, J. Heidemann and D. Estrin, Energy-Efficient MAC Protocol for Wireless Sensor Networks, Proceedings of the Twenty First International Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM 2002), New York, NY, USA, June 23-27 2002.

[Buttyan+ 2002] L. Buttyan and J.-P. Hubaux, Report on a Working Session on Security in Wireless Ad Hoc Networks, Mobile Computing and Communications Review, Volume 6, Number 4.

mac protocols and security in ad hoc and sensor networks

Documents

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power control mac protocol

power control mac pcm

physical carrier sensing

virtual carrier sensing

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packet transmission