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WSN NETWORK -MAC PROTOCOLS - 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
- 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
- 23. Message passing RTS and CTS mechanism is used to send data