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Efficient MAC Protocols for Wireless Sensor Networks. Mahendra Kumar. Properties of a Well Defined MAC Protocol . Energy Efficient Scalability Adaptability to changes in network topology Latency, throughput, bandwidth Fairness –not so important. Reason of Energy Waste. Collision

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properties of a well defined mac protocol
Properties of a Well Defined MAC Protocol
  • Energy Efficient
  • Scalability
  • Adaptability to changes in network topology
  • Latency, throughput, bandwidth
  • Fairness –not so important
reason of energy waste
Reason of Energy Waste
  • Collision
  • Overhearing
  • Control Packet overhead
  • Idle Listening
  • Overremitting
existing mac protocols
Existing MAC Protocols
  • Sensor-MAC (S-MAC) : Listen-sleep
  • Timeout-MAC (T-MAC) : Activation event
  • WiseMAC : Preamble Sampling
s mac
  • Main goal –reduce power consumption
  • Three major components:
    • Periodic sleep-listen
    • Collision and overhearing avoidance
    • Message passing
periodic sleep listen
Periodic Sleep-Listen
  • Each node goes to sleep for some time,

and then wakes up and listens to see if any other node wants to talk to it.

  • During Sleep it turn off its radio.
collision and overhearing avoidance
Collision and Overhearing Avoidance
  • Interfering nodes go to sleep after they hear an RTS or CTS packet.
  • Duration field in each transmitted packet indicates how long the remaining transmission will be.
maintaining synchronization
Maintaining Synchronization
  • The listen/sleep scheme requires synchronization among neighboring nodes.
  • Updating schedules is accomplished by sending a SYNC packet.
advantages disadvantages
  • Energy waste caused by idle listening is reduced by sleep schedules.
  • Sleep and listen periods are predefined and constant which decreases the efficiency of the algorithm under variable traffic load.
timeout mac t mac
Timeout-MAC (T-MAC)
  • Proposed to enhance the poor results of S-MAC protocol under variable traffic load.
  • Listen period ends when no activation event has occurred for a time threshold TA.
  • Reduce idle listening by transmitting all messages in bursts of variable length, and sleeping between bursts.
  • times out on hearing nothing.
advantages disadvantages13
  • Gives better result under variable load.
  • Suffers from early sleeping problem –node goes to sleep when a neighbor still has messages for it.
  • All nodes defined to have two communication channels.
  • Data channel uses TDMA
  • Control channel uses CSMA
  • Preamble sampling used to decrease idle listening time.
  • Nodes sample the medium periodically to see if any data is going to arrive.
advantages disadvantages16
  • Dynamic preamble length adjustment results in better performance.
  • Conflict when one node starts to send the preamble to a node that is already receiving another node’s transmission where the preamble sender is not within range. Hidden terminal problem
other mac protocols
Other MAC Protocols
  • SIFT :Event Driven
  • TRAMA : Traffic Adaptive MAC, TDMA Based