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Comparison of XMAC and BMAC Protocols

Comparison of XMAC and BMAC Protocols. Performance Evaluation of Computer Systems and Networks (CS681) Course Project. Vijay Gabale (07305004) Ashutosh Dhekne (07305016). Outline. Motivation X-MAC, B-MAC protocols Implementation Architecture Simulation Metrics Experiments and results

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Comparison of XMAC and BMAC Protocols

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  1. Comparison of XMAC and BMAC Protocols Performance Evaluation of Computer Systems and Networks (CS681) Course Project Vijay Gabale (07305004) Ashutosh Dhekne (07305016)

  2. Outline • Motivation • X-MAC, B-MAC protocols • Implementation • Architecture • Simulation • Metrics • Experiments and results • Conclusion Performance Evaluation Project Presentation, CSE, IIT Bombay

  3. Motivation • Comparison of the two protocols • Experimenting with multi hop routes • Investigate energy savings and latency deficits • Interesting Questions • What are the load conditions under which X-MAC outperforms B-MAC (or vice versa) • What is the upper bound on end-to-end latency? • Given a lifetime of the network, what should be the sleep period? Performance Evaluation Project Presentation, CSE, IIT Bombay

  4. The Protocols • Both are asynchronous protocols for wireless sensor networks • Data transfer across duty cycled nodes is the primary objective • Constraints on energy available at the node • Sampling frequency is usually very low, possibly once in few minutes • Use of preamble to inform neighbor about impending data transfer Performance Evaluation Project Presentation, CSE, IIT Bombay

  5. Difference in preamble mechanism • BMAC sends a long continuous preamble • XMAC sends short strobes • Target ID is encoded in the XMAC strobe Performance Evaluation Project Presentation, CSE, IIT Bombay

  6. Implementation • CSMA/CA protocol • Lossless wireless medium – global buffers • Grid network as well as linear topology • Simulated individual node – use thread! • Scheduling unpredictability – use locks! • Per node measurement – thread-specific clock! • Randomness inherent to scheduling of threads Performance Evaluation Project Presentation, CSE, IIT Bombay

  7. Architecture Channel Busy? No Yes 1 2 3 4 5 6 7 8 Wait till timeout / Free Channels Timeout? No Yes 3 Lock channel Do Processing Unlock Channel Sleep Performance Evaluation Project Presentation, CSE, IIT Bombay

  8. B MAC Data Send and Receive 1 2 3 1 3 Preamble 2 Data Ack Transmitter Conditioned Wait Receiver Condition Wait Transmitter Lock Receiver Lock Transmitter Unlock Receiver Unlock Performance Evaluation Project Presentation, CSE, IIT Bombay

  9. X MAC Data Send and Receive • Receiver woke up in between a strobe wasBusy Ack Data Ack Transmitter Conditioned Wait Receiver Conditioned Wait Transmitter Lock Receiver Lock Transmitter Unlock Receiver Unlock Performance Evaluation Project Presentation, CSE, IIT Bombay

  10. X MAC Data Send and Receive • Receiver woke up when channel was free wasFree Ack Data Ack Transmitter Conditioned Wait Receiver Conditioned Wait Transmitter Lock Receiver Lock Transmitter Unlock Receiver Unlock Performance Evaluation Project Presentation, CSE, IIT Bombay

  11. System parameters and Metrics • System parameters • Sleep time • Number of nodes • Number of transmitters • Strobe interval • Metrics • Energy • Latency • Duty cycle Performance Evaluation Project Presentation, CSE, IIT Bombay

  12. How protocols behave for different sleep times? • Set up • Nodes: 9 (Grid) • Sleep time: 10ms to 50ms • Measure • Energy B-MAC requires more energy than X-MAC at any sleep time. Moreover, energy required increases with increased sleep time. It is so due to the overhead of listening to the long preamble in B-MAC Performance Evaluation Project Presentation, CSE, IIT Bombay

  13. How protocols behave for different sleep times? • Set up • Nodes: 9 (Grid) • Sleep time: 10ms to 50ms • Measure • Latency B-MAC requires more time to transfer packets from the source to the destination. This is because the entire preamble has to be always sent, even though the receiver was already awake. X-MAC saves this time. Performance Evaluation Project Presentation, CSE, IIT Bombay

  14. How protocols behave with respect to duty cycling? • Set up • Nodes: 10 • Sleep time: 10ms • Measure • Duty Cycle X-MAC not only completes a transfer faster, it also allows lower duty cycling. Performance Evaluation Project Presentation, CSE, IIT Bombay

  15. How protocols behave for different number of nodes? • Set up • Nodes: 4 to 10 • Sleep time: 10ms • Measure • Energy Energy required to transfer data obviously increases with number of intermediate hops. However, for B-MAC, it increases faster than that for X-MAC. This is a benefit of using strobe preamble. Performance Evaluation Project Presentation, CSE, IIT Bombay

  16. How protocols behave for different number of nodes? • Set up • Nodes: 4 to 10 • Sleep time: 10ms • Measure • Latency B-MAC almost always requires more time to transfer packets end to end. With increasing nodes, this time does not increase as fast as we would have expected. Performance Evaluation Project Presentation, CSE, IIT Bombay

  17. How protocols behave for different number of transmitters (data originators)? • Set up • Nodes: 12 (Grid) • Sleep time: 10ms • Transmitters: 1 to 3 • Measure • Total Energy We expect the total energy required to increase. However, we confined ourselves to only 3 experiments. Performance Evaluation Project Presentation, CSE, IIT Bombay

  18. How protocols behave for different strobe intervals? • Set up • Nodes: 9 • Sleep time: 10ms • Strobe Interval 500 to 3500 • Measure • Latency With increased strobe interval, the X-MAC comes closer to B-MAC. The reason why the graph shows a downward trend after 2500 is yet under investigation. We suspect there exists some relation with the sleep time. Performance Evaluation Project Presentation, CSE, IIT Bombay

  19. How much energy will be required? • Set up • Nodes: 9 • Sleep time: 10ms to 50ms • Measure • Energy Given a certain energy constraint on the network, we can choose the appropriate sleep time. This directly translates to the expected lifetime of the network. Energy (J) = Power (W) * Time (sec) Performance Evaluation Project Presentation, CSE, IIT Bombay

  20. How much latency to expect? • Set up • Nodes: 9 • Sleep time: 10ms to 50ms • Measure • Latency Increasing the sleep time does not help B-MAC. Both energy as well as latency worsen. With X-MAC, the energy slightly dips at an optimal sleep period. Latency almost monotonically increases with sleep period. Performance Evaluation Project Presentation, CSE, IIT Bombay

  21. Conclusion • X-MAC outperforms B-MAC in both energy consumed and the latency of end to end packet transfer • X-MAC offers better duty cycling opportunities—nodes sleep for more time • Nevertheless, the “Sleep time” system parameter must be judiciously chosen for optimal performance Performance Evaluation Project Presentation, CSE, IIT Bombay

  22. References • Michael Buettner, Gary V. Yee, Eric Anderson, Richard Han. X-MAC: A Short Preamble MAC Protocol for Duty-Cycled Wireless Sensor Networks. Sensys ’06. • J. Polastre, J. Hill, and D. Culler. Versatile low power media access for wireless sensor networks. In The Second ACM Conference on Embedded Networked Sensor Systems (SenSys), pages 95–107, November 2004. • Confidence Interval calculation in http://www.cse.usf.edu/~christen/tools/toolpage.html • Confidence interval general information from http://en.wikipedia.org/wiki/Confidence_interval and http://en.wikipedia.org/wiki/Student%27s_t-distribution Performance Evaluation Project Presentation, CSE, IIT Bombay

  23. Thank you

  24. Confidence Interval Calculations • 90% confidence interval • Calculated using the formula: Sqrt(Variance) Number of samples Mean Table Lookup Performance Evaluation Project Presentation, CSE, IIT Bombay

  25. Division of work • B-MAC, X-MAC frame formats • Sensor network design • Threading architecture • Measurements • Shell, Python scripting • One is alone, two is company, three is crowd! Performance Evaluation Project Presentation, CSE, IIT Bombay

  26. Software requirements • The simulation program is created in C • Uses shell script, python script and gnuplot for producing results • We require the pthread library and the math library to be installed. (–lpthread –lrt –lm libraries required) • GNUPlot 4.2 for the histogram graphs. Performance Evaluation Project Presentation, CSE, IIT Bombay

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