1. Slow Start Backoff Algorithm for Wireless Ad Hoc Networks Der-Jiunn Deng Department of Computer Science and Information Engineering National Changhua University of Education

3. Ad Hoc Networks Ad hoc network: mobile stations can dynamically form network without AP Applications: –“laptop” meeting in conference room, car –interconnection of “personal” devices –battlefield IETF MANET (Mobile Ad hoc Networks) working group

4. CSMA/CA CSMA: sender - if sense channel idle for DISF sec. then transmit entire frame (no collision detection) -if sense channel busy then binary backoff CSMA receiver: if received OK return ACK after SIFS

5. CSMA: others NAV: Network Allocation Vector 802.11 frame has transmission time field others (hearing sata) defer access for NAV time unitsCSMA/CA

6. Destination Data ACK Basic Access Method (CSMA/CA) Basic Access Method (CSMA/CA) Source Other DIFS Busy Medium DIFS Free access when medium is free longer than DIFS CW SIFSDIFS Busy Medium DIFS Busy Medium CW DIFS NAV DIFS Busy Medium DIFS Busy Medium DIFS Busy Medium Defer access Select a CW size and decrement backoff as long as medium is idle

7. Binary Exponential Backoff (BEB) Data DIFS Busy Medium DIFS CW DIFS Busy Medium SIFS 31 0 63 127 255 511 1023 initial attempt first retransmission second retransmission third retransmission forth retransmission CW minCW max time slot ACK

8. r The usage of backoff algorithm avoids long access delays when the load is light because it selects an initial (small) parameter value of contention window (CW) by assuming a low level of congestion in the system. r This strategy might allocate initial size of CW, only to find out later that it is not enough when the load increased, but each increase of the CW parameter value is obtained paying the cost of a collision (bandwidth wastage) r After a successful transmission, the size of CW is set again to the minimum value without maintaining any knowledge of the current channel status. Congested Scenario

9. LILD

10. EIED

11. Slow Start Backoff Alg.

12. SSB

13. SSB

14. Impact of Different Threshold

16. Slow-Start Backoff Alg. 1111 111 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

17. 012xmm-1 Saturation Throughput Analysis

18. Let Saturation Throughput Analysis

20. XXXXX 1st2nd3rdxnd 1-p p XXX Geometric Distribution Consider a sequence of Bernoulli trails with the probability of success on being P. Let r.v. X denote the number of trials up to and including the first success

21. Geometric Distribution Consider a sequence of Bernoulli trails with the probability of success on being P. Let r.v. X denote the number of trials up to and including the first success

22. ACK P-Persistent CSMA/CA Data DIFS Busy Medium DIFS CW DIFS Busy Medium SIFS Data defer accessdecrement backoff as long as medium is idle

23. Saturation Throughput Analysis

25. Optimal CW size

26. Simulation Results

29. IEICE (Jan. 1999)

30. IEEE JSAC (Jun. 2005)

31. IEEE TWC (Dec. 2008)

32. IEICE (Jan. 1999)

33. IEEE JSAC and IEEE TWC

34. Based on the history –Telephone network (PSTN) –Computer network and mobile phone network Internet and the G stuff (GSM/GPRS/3G) –Wireless networks (WLANs) PSTN G stuff Internet 80‘s90’s00‘s now WLANs 10‘s Forward Looking

35. PSTN G stuff Internet 80‘s90’s00‘s now WLANs 10‘s

36. PSTN G stuff Internet 80‘s90’s00‘s now WLANs 10‘s

37. PSTN G stuff Internet 80‘s90’s00‘s now WLANs 10‘s