1. A QoS MAC Protocol for Differentiated Service in Mobile Ad Hoc Networks Chi-Hsiang Yeh, Tiantong You Queen’s University ICPP 2003’

2. Outline Introduction PICK PIC Negative/Implicit ACK Performance Conclusion

3. Introduction 802.11 and 802.11e are design for WLANs, rather then ad hoc networks. 802.11e are base on Persistent factors(PFs) for backoff Arbitrary interframe space(AIFS) for the idle detection time These mechanisms will work well in single-hop WLANs

4. Introduction 802.11e can’t provide small and bounded delay to high-priority packet in a multihop environment Block by nearby transmissions/receptions of low priority packets RTS/CTS messages collision (30%) Data packets collision (10%) The delay can’t be bounded due to Repeated RTS/CTS dialogues Data packet retransmissions

5. Introduction Periodical reservation-based MAC protocols are not collision-free due to the mobility of ad hoc networks

6. PICK Priority ID Countdown with negative/implicit ACK Goals Priority Short/long-term fairness Low collision rate Smaller control channel overhead Distributed MAC protocol

7. Priority ID Countdown(PIC) Wireless stations (WS) select an competition number to join a new round of binary countdown competition Wireless station with the biggest competition number is winner that can transmit its RTS, CTS or other control messages

8. Priority ID Countdown(PIC) An example of competition number (CN) 10011001 Device a Binary countdown slot

9. The Competition The binary countdown competition The frame formation for the control channel of PICK 1.Synchronization 2.Start competition with the same bit-slot

10. The Competition If bit-slot i is 1 then transmits a “pulse signal” to all the WSs with in a distance of 2R 10011001 Device a a R 2R R: Transmission range Pulse Signal

11. The Competition If bit-slot i is 0 then keeps silent and senses whether there is any pulse signal 10011001 Device a a R 2R R: Transmission range Sensing…

12. The Competition If WS’s bit-slot i is 0 and senses pulse signal, then this WS is kicked out the competition Such surviving WS per bit slot whose CN=1 CN=0 but don’t sense any Pulse Signal Final Survivor is the winner that can transmit its RTS, CTS or other control messages

13. The Competition Example

14. Competition Number Generation CN with unique ID CN compose of priority number,random number and unique ID Must be only one winner 100% Collision-Free Control channel overhead 10011001 Device a Priority Number Random NumberUnique ID

15. Competition Number Generation CN without unique ID CN compose of priority number and random number Lower control overhead Low control message rate collision 0% data packet collision 10011001 Device a Priority Number Random Number

16. Competition Number Generation 11The Highest Priority 10High Priority 01Medium Priority 00Low Priority Priority Level

17. Negative/Implicit ACK NI-ACK If receiver fails to receive the scheduled data packet, it will reply a negative ACK, otherwise it remain silent(implicit ACK). When transmitter receives a NAK, it will send an RTS to schedule for a retransmission. Transmitter Receiver R T Succeeded Silent R T failedNAK RTS

18. Negative/Implicit ACK Reason Smaller overhead in control channel Less ACK will compete for the control channel of PICK under heavy traffic load No expose terminal problem ABCD

19. Performance 80 WSs in 400X400-unit grid area Transmission Radius R=100 grid unit Mobility Model 1 unit/s moving speed 4 seconds pause time Exponential distribution

25. PICK with packet arrival rate is 80 MT/s Dual-channel 802.11e with packet arrival rate is 80 MT/s

26. Conclusion Collision-free in date channel and low collision rate in control channel does not rely on busy tone and additional transceiver Support prioritization and DiffServ in multihop ad hoc network Short/long-term fairness

27. Thank you…