Sensys2010

1. PIP: A Connection-Oriented, Multi-Hop, Multi-Channel TDMA-based MAC for High Throughput Bulk Transfer Sensys2010

2. Outline • Introduction • Design of PIP • Performance evaluation • Conclusion

3. Introduction • Goal: high throughput bulk data transfer • Interference • Intra-path interference • Inter-path interference • External interference • Feature • Multi-hop connection oriented • TDMA-based • Multi-channel • Centralized relay sink source

4. Introduction • Flush • distributed • Single-channel • CSMA

5. Design of PIP • EOF • (End-of-File) • SNACK • (Selective Negative Acknowledgement)

6. PIP MAC Protocol • 3 modes of operation • U1C (unsynchronized, single-channel) • UMC (unsynchronized, multi-channel) • SMC (synchronized, multi-channel) • Reserve one channel for U1C mode • SMC is used during data transfer

7. Connection Setup • Assign every node in the path a designated receiving channel for UMC and SMC modes • Schedule, with spatial reuse • After forwarding ConnReq, a node changes from U1C to UMC mode 16 15 14 13 12

8. Time Synchronization • Time stamp is piggy-backed in data packet • On reception of first Data, a node changes from UMC to SMC mode • No transmission in UMC mode • Data source is the clock source of the path

9. EOF, SNACK exchange • Have packet only on one direction at a time • Data sink send SNACK packets only when triggered by an EOF from the source

10. Connection Tear-down • After forwarding TearDown, a node changes from SMC to U1C mode • Send by source to avoid TearDown loss • Hop-by-hop ACKs

11. Example

12. State Diagram

13. PIP Prototype Implementation • Pipeline radio and SPI (Serial Peripheral Interface )

14. PIP Prototype Implementation • Time slot schedule 4 3 2 1 0

15. PIP Prototype Implementation • Time synchronization requirement • Multi-channel, sync neighbors

16. PIP Throughput Optimality • Single flow • Sink is busy only half of the time (receiving only) • Close to 50% of optimal throughput • Two flow can achieve optimal throughput • All node time sync to sink, not source • Avoid inter-path interference

17. PIP Performance Evaluation • Markov analysis • Model buffer occupancy at each node as discrete time Markov chain • Input/output: throughput • Simulation-based evaluation • Prototype implementation • 10-node, 9-hop • Given forwarding table • Emulate wireless channel loss: drop packets probabilistically (error rate) • 1000 packets, 124 bytes, 32KHz clock, 1tick = 30.5us

18. Duration and Queue Size • Frame duration is 430 ticks (13ms) • Slot: 200 ticks, guard time: 15 ticks • Queue size • 10

19. Comparison of analysis, simulation, and implementation

20. Throughput as a function of error rate

21. External interference and channel hopping

22. Comparison to others

23. Comparison to others (simulation)

24. Non-requirement of flow-control

25. Conclusion • Throughput degrades only slightly with increasing number of hops • Robust to variable wireless error rates • Performs well even without any flowcontrol • Requires only small queue sizes to operate well