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S-MAC Sensor Medium Access Control Protocol An Energy Efficient MAC protocol for Wireless Sensor...
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Transcript of S-MAC Sensor Medium Access Control Protocol An Energy Efficient MAC protocol for Wireless Sensor...
S-MAC S-MAC Sensor Medium Access Sensor Medium Access
Control ProtocolControl Protocol
An Energy Efficient MAC protocol An Energy Efficient MAC protocol for Wireless Sensor Networksfor Wireless Sensor Networks
OutlineOutline
IntroductionIntroductionDesign ConsiderationsDesign ConsiderationsMain sources of energy inefficiencyMain sources of energy inefficiencyCurrent MAC designCurrent MAC designS-MACS-MACProtocol implementation in a test-bedProtocol implementation in a test-bedDiscussionDiscussionConclusion and future workConclusion and future work
Wireless Sensor NetworksWireless Sensor Networks
Application specific wireless networks for Application specific wireless networks for monitoring, smart spaces, medical monitoring, smart spaces, medical systems and robotic exploration systems and robotic exploration
Battery operated and power limited sensor Battery operated and power limited sensor devicesdevices
Large number of distributed nodes Large number of distributed nodes deployed in an ad-hoc fashiondeployed in an ad-hoc fashion
Design ConsiderationsDesign Considerations
Primary attributes:Primary attributes:Energy EfficiencyEnergy Efficiency
often difficult to recharge or replace batteriesoften difficult to recharge or replace batteries
prolonging the network lifetime is importantprolonging the network lifetime is important
ScalabilityScalability Some nodes may die or new nodes may joinSome nodes may die or new nodes may join
Secondary attributes:Secondary attributes:Fairness, latency, throughput and bandwidthFairness, latency, throughput and bandwidth
Sources of Energy InefficiencySources of Energy Inefficiency
CollisionCollision
OverhearingOverhearing
Control packet overheadControl packet overhead
Idle listeningIdle listening
Existing MAC DesignExisting MAC Design
Contention-based protocolsContention-based protocols• IEEE 802.11 – Idle listeningIEEE 802.11 – Idle listening• PAMAS – heavy duty cycle of the radio, PAMAS – heavy duty cycle of the radio,
avoids overhearing, idle listening avoids overhearing, idle listening
TDMA based protocolsTDMA based protocols
Advantages - Reduced energy consumptionAdvantages - Reduced energy consumption
Problems – requires real clusters, Problems – requires real clusters,
and does not support scalability and does not support scalability
Design goal of S-MACDesign goal of S-MAC
Reduce energy consumptionReduce energy consumption
Support good scalability Support good scalability
Self-configurableSelf-configurable
S-MACS-MAC
Tries to reduce wastage of energy from all Tries to reduce wastage of energy from all four sources of energy inefficiencyfour sources of energy inefficiency
Collision – by using RTS and CTSCollision – by using RTS and CTS Overhearing – by switching the radio off Overhearing – by switching the radio off
when transmission is not meant for that when transmission is not meant for that nodenode
Control Overhead – by message passingControl Overhead – by message passing Idle listening – by periodic listen and sleepIdle listening – by periodic listen and sleep
Is the improvement free of cost?Is the improvement free of cost?
NoNo
In exchange there is some reduction in In exchange there is some reduction in per-hop fairness and latencyper-hop fairness and latency
But does not reduce end-to-end fairness But does not reduce end-to-end fairness and latencyand latency
Is it important for sensor networks?Is it important for sensor networks?
Network AssumptionsNetwork Assumptions
Composed of many small nodes deployed Composed of many small nodes deployed in ad hoc fashionin ad hoc fashion
Most communication will be between Most communication will be between nodes as peers, rather than a single base nodes as peers, rather than a single base stationstation
Nodes must self-configureNodes must self-configure
Application AssumptionsApplication Assumptions
Dedicated to a single applicationDedicated to a single applicationor a few collaborative applicationor a few collaborative application
Involves in-network processing to reduce Involves in-network processing to reduce traffic and increase life timetraffic and increase life time
Applications will have long idle periods Applications will have long idle periods and can tolerate some latencyand can tolerate some latency
Components of S-MACComponents of S-MAC
Periodic listen and sleepPeriodic listen and sleep
Collision and Overhearing avoidanceCollision and Overhearing avoidance
Message passingMessage passing
Periodic Listen and SleepPeriodic Listen and Sleep
Each node goes into periodic sleep mode Each node goes into periodic sleep mode during which it switches the radio off and during which it switches the radio off and sets a timer to awake latersets a timer to awake later
When the timer expires, it wakes up When the timer expires, it wakes up
Selection of sleep and listen duration is Selection of sleep and listen duration is based on the application scenariosbased on the application scenarios
Neighboring nodes are synchronized Neighboring nodes are synchronized togethertogether
Contd….Contd….
Nodes exchange schedules by broadcastNodes exchange schedules by broadcast
Multiple neighbors contend for the mediumMultiple neighbors contend for the medium
Once transmission starts, it does not stop Once transmission starts, it does not stop until completeduntil completed
A B C D
Choosing and Maintaining Choosing and Maintaining SchedulesSchedules
Each node maintains a schedule tableEach node maintains a schedule table
Initial schedule is establishedInitial schedule is established SynchronizerSynchronizer FollowerFollower
Rules for joining a new nodeRules for joining a new node
Maintaining SynchronizationMaintaining Synchronization
Needed to prevent clock driftNeeded to prevent clock driftPeriodic updating using a SYNC packetPeriodic updating using a SYNC packet
Receivers adjust their timer countersReceivers adjust their timer countersListen interval divided into two partsListen interval divided into two parts
Each part further divided into time slots Each part further divided into time slots
Sender Node ID Next-Sleep Time
SYNC Packet
Timing Relationship Timing Relationship
Collision AvoidanceCollision Avoidance
Similar to IEEE 802.11 using RTS/CTS Similar to IEEE 802.11 using RTS/CTS mechanismmechanism
Perform virtual and physical carrier sense Perform virtual and physical carrier sense before transmissionbefore transmission
• RTS/CTS addresses the hidden terminal RTS/CTS addresses the hidden terminal problemproblem
• NAV –indicates how long the remaining NAV –indicates how long the remaining transmission will be.transmission will be.
Overhearing AvoidanceOverhearing Avoidance
Interfering nodes go to sleep after they hear Interfering nodes go to sleep after they hear the RTS or CTS packetthe RTS or CTS packet
The medium is busy when the NAV value is The medium is busy when the NAV value is not zero not zero
All immediate neighbors of sender and All immediate neighbors of sender and receiver should go to sleepreceiver should go to sleep
Message PassingMessage Passing
What is a message?What is a message?
Transmitting a message as a long packetTransmitting a message as a long packet
High retransmission costHigh retransmission cost
Fragmentation into small packetsFragmentation into small packets
High control overheadHigh control overhead Solution Solution DisadvantageDisadvantage
Protocol ImplementationProtocol Implementation
Test bedTest bed• Rene motes developed at UCBRene motes developed at UCB• They run TinyOS, an event–driven operating They run TinyOS, an event–driven operating
systemsystem Two types of packetsTwo types of packets• Fixed size data packets with header(6B), Fixed size data packets with header(6B),
payload(30B) and CRC(2B)payload(30B) and CRC(2B)• Control packets (RTS and CTS), header(6B)Control packets (RTS and CTS), header(6B)
(2B) CRC(2B) CRC
MAC modules implementedMAC modules implemented
Simplified IEEE 802.11 DCF – physical Simplified IEEE 802.11 DCF – physical and virtual carrier sense, backoff and retry, and virtual carrier sense, backoff and retry, RTS/CTS/DATA/ACK packet exchange RTS/CTS/DATA/ACK packet exchange and fragmentation supportand fragmentation support
Message passing with overhearing Message passing with overhearing avoidanceavoidance
The complete S-MAC – all the features are The complete S-MAC – all the features are implementedimplemented
Conclusions and Future workConclusions and Future work
S-MAC has good energy conserving S-MAC has good energy conserving properties comparing to IEEE 802.11properties comparing to IEEE 802.11
Future workFuture work
Analytical study on the energy Analytical study on the energy consumption and latencyconsumption and latency
Analyze the effect of topology changesAnalyze the effect of topology changes
Our ProjectOur Project
Implementing S-MAC on TinyOS 1.0Implementing S-MAC on TinyOS 1.0
Incorporating multicasting with S-MACIncorporating multicasting with S-MAC
Directed Diffusion and S-MACDirected Diffusion and S-MAC
S-MAC can be incorporated into the S-MAC can be incorporated into the directed diffusion paradigmdirected diffusion paradigm