WSN NETWORKING CONCEPTS AND PROTOCOLS MAC Protocols for Wireless Sensor Networks, Low Duty Cycle Protocols And Wakeup Concepts – S-MAC,

1. Dr.Arun Chokkalingam
Professor
Department of Electronics and Communication
RMK College of Engineering and Technology
Chennai.
UNIT III
WSN NETWORK MAC PROTOCOLS
Low Duty Cycle Protocols And Wakeup Concepts –
S-MAC

2. Content
WSN NETWORKING CONCEPTS AND PROTOCOLS
 MAC Protocols for Wireless Sensor Networks,
 Low Duty Cycle Protocols And Wakeup Concepts –
 S-MAC,

3. Medium Access Control (MAC) protocols

4. Importance of MAC Protocols
Medium access control (MAC) protocols:
They coordinate the times where a number of nodes
access a shared communication medium.

5. Objectives of this Unit
 The single most important requirement is energy efficiency
 There are different MAC-specific sources of energy waste to consider:
1. Overhearing,
2. Collisions,
3. Overhead,
4. Idle listening.
 We discuss protocols addressing one or more of these issues.
 One important approach is to switch the wireless transceiver into a
sleep mode.

6. MAC Protocols for Wireless Sensor Networks
 Specific requirements and design considerations for MAC protocols in
wireless sensor networks.
 Balance of requirements
 Energy problems on the MAC layer or Major Sources of Energy Waste
1. Collisions,
2. Overhearing,
3. Overhead,
4. Idle listening.

7. Cont.
 Balance of requirements
 The importance of energy efficiency for the design of MAC protocols is
relatively new and many of the “classical” protocols like ALOHA and
CSMA contain no provisions toward this goal.
 Other typical performance figures like fairness, throughput, or delay
tend to play a minor role in sensor networks.
 Important requirements for mac protocols are scalability and
robustness against frequent topology changes

8. Energy problems on the MAC layer
 A nodes transceiver consumes a significant share of energy.
 Transceiver can be in one of the four main states : transmitting,
receiving, idle and sleeping.
 sleeping can be significantly cheaper than Idle state.

9. Major Sources of Energy Waste
1. Collisions,
2. Overhearing,
3. Overhead,
4. Idle listening.

10. Cont.

11. Cont.

12. Cont.
c) Ideal listening
 Nodes listen to channel for possible traffic. If nothing is sensed then
most of the time nodes is ideal.
 Ideal listening consume 50-100% energy required to receive packets.
d) Protocol overhead
 Protocol overhead is induced by MAC-related control frames like, RTS and CTS
packets or request packets in demand assignment protocols, and furthermore
by per-packet overhead like packet headers and trailers.

13. Types of MAC Protocols
 Low Duty Cycle Protocols And Wakeup Concepts –
 S-MAC,
 The Mediation Device Protocol
 Contention based protocols – PAMAS,
 Schedule based protocols – LEACH,
 IEEE 802.15.4 MAC protocol,

14. Low duty cycle protocols and wakeup concepts
 Low duty cycle protocols try to avoid spending (much) time in the
idle state and to reduce the communication activities of a sensor node
to a minimum.
 wakeup radio-the sleep state is left only when a node is about to
transmit or receive packets.

15. periodic wakeup scheme
 The cycled receiver approach, nodes spend most of their time in the sleep
mode and wake up periodically to receive packets from other nodes.
 A node a listens onto the channel during its listen period and goes back into
sleep mode when no other node takes the opportunity to direct a packet to a.
 A potential transmitter B must acquire knowledge about a’s listen periods to
send its packet at the right time
 A whole cycle consisting of sleep period and listen period is also called a
wakeup period.
 The ratio of the listen period length to the wakeup period length is also
called the node’s duty cycle.

16. Cont.
• By choosing a small duty cycle, the transceiver is in sleep mode
most of the time, avoiding idle listening and conserving energy.
• In heavy load situations significant competition can occur.
• Choosing a long sleep period induces a significant per-hop
latency,.
• In the multihop case, the per-hop latencies add up and create
significant end-to-end latencies.
• Sleep phases should not be too short in case the start-up costs
outweigh the benefits.

17. S-MAC (Sensor- Medium Access Control)
1. Periodic listen and sleep
2. Collision and overhearing avoidance
3. Message passing
Periodic listen and sleep
 Every node sleep for some time and then walkup to see any other node
wants to talk to him
 During sleep time node turn off its radio to save Energy

18. Schedule maintenance

19. Maintaining Synchronization
 Collision avoidance?
 Schedules are periodically broadcasted to neighbour
 Schedules are sent in SYNC packet.
 Listen time is divided into two potions one for SYNC and another for
Data.

20. SYNC or data sending

21. data sending

22. Overhearing Avoidance

23. Message passing
RTS and CTS mechanism is used to send data

25. Reference
 https://www.youtube.com/watch?v=Q9nez9IMC3M
 https://www.youtube.com/watch?v=FmE1b7ETVd0