1. SEEDEX: A MAC protocol for ad hoc networks R. Rozovsky and P. R. Kumar ACM ACM MobiHoc 2001 speaker: Chien-Wen

2. Outline INTRODUCTION THE IEEE 802.11 PROTOCOL THE SEEDEX MAC PROTOCOL SIMULATION CONCLUSION

3. INTRODUCTION to avoid collisions without making explicit reservation to employ a random schedule pseudo-random number generator exchanging the seeds within a two- hop neighborhood

4. THE IEEE 802.11 PROTOCOL

5. the wasteful scenarios –two neighborhoods are silenced –four way handshake –Backoff scheme

6. SEEDEX: CHOOSING A RANDOM SCHEDULE preface –all nodes could publish their schedules –two states L: listening PT: possibly sending

7. choosing a slot as follows –Node T is in state PT –Node R is in state L –All of node R's neighbors are in state L SEEDEX: CHOOSING A RANDOM SCHEDULE

8. use an i.i.d. Bernoulli sequence With probability p to be PT state using random schedule SEEDEX: CHOOSING A RANDOM SCHEDULE

9. THE CENTRAL IDEA OF SEEDEX the i.i.d. Bernoulli schedule –the use of a pseudo-random number generator –initial value is called the “ seed ” publishing random schedules by exchanging seeds

10. THE CENTRAL IDEA OF SEEDEX exchanging seeds –two-hop neighborhood –fan-in and fan-out fan-out –broadcasts the seeds to all its neighbors fan-in –hearing a similar broadcast from each of its neighbors

12. SEEDEX: CHOOSING A RANDOM SCHEDULE

13. WHEN DOES A NODE TRANSMIT A PACKET? Waiting for a slot –Sender is in PT state –Receiver is in L state –if Other neighbors of Rx are in L state then transmit Else Min{α/n+1, 1} //n is the num. of others which are in PT state

14. WHEN DOES A NODE TRANSMIT A PACKET? The use of α –a Possibly Transmit state –in light traffic α ≒ 2.5 –in heavy traffic α ≒ 1.5

16. WHAT IS A GOOD CHOICE OF P? node T is in PT state

17. WHAT IS A GOOD CHOICE OF P? node R is in L state

18. WHAT IS A GOOD CHOICE OF P? j other neighbors are in PT state, and the remaining neighbors are in L state

19. WHAT IS A GOOD CHOICE OF P? Only node T decides to trans.

20. WHAT IS A GOOD CHOICE OF P? When N=6, p =0.246

21. WHAT IS A GOOD CHOICE OF P? Optimal p =0.21

22. SIMULATION RESULT ： SOME PERFORMANCE NUMBERS Conducted on NS 100 nodes chooses a random neighboring recipient for each packet

23. SIMULATION RESULT ： SOME PERFORMANCE NUMBERS

24. USING SEEDEX FOR RTS RESERVATIONS using SEEDEX only on the RTS packet

25. SIMULATION RESULT ： PERFORMANCE COMPARISON OF SEEDEX-R WITH IEEE 802.11

28. CONCLUSION Avoid making reservations Does not employ backoff scheme Does not require silencing both neighbors of Tx and Rx

29. Futher Investigation Fan-in procedure The adaption of α Impact of topology

30. Disscusion T R PT L L L L L T R L L L L α /n+1 Hidden Probability ！！

31. Disscusion T R PT L L L L T R L L L L Exposed transmitt ！！

32. Disscusion T R PT L L L L T R L L L Collision?? PT α /2

33. Disscusion T R PT L L L L T R L L L Probability ！！ PT α /2