1. Courtesy Piggybacking: Supporting Differentiated Services in Multihop Mobile Ad Hoc Networks Wei LiuXiang Chen Yuguang Fang WING Dept. of ECE University of Florida

2. Outline Introduction and motivation of CP Design issues –Packet-length-based channel model –Harvesting of unused bandwidth –Courtesy Piggybacking (CP) scheme Performance Evaluation Conclusions

3. Problems Support of heterogeneous traffic in multihop ad hoc networks –Special features of ad hoc networks time-varying and error-prone wireless links. dynamic and limited bandwidth. time-varying traffic pattern and user location. limited energy. –Solution reliable mobile communications: routing, MAC, etc. QoS provisioning: service differentiation mechanism, scheduling mechanisms. –Problem Conflict between throughput and fairness, starvation. Utilize channel dynamics and traffic dynamics

4. Motivation A tunnel scenario ( the Whittier Tunnel in Alaska) Piggybacking can relieve the conflict between different transportation. Piggybacking policy (How Many-Which problem)

5. Questions Where does the free space (unused BW) come from? How can we utilize this free space? What criteria should we use when piggybacking ? Can we apply this piggybacking idea to solve the networking problem: solving conflict between throughput and fairness when supporting heterogeneous traffic in multihop ad hoc networks? Yes

6. Design Issues Packet-length-based channel model Where is the free space : Channel Dynamics and Traffic Dynamics How to utilize the free space: Courtesy Piggybacking

7. Packet-length-based Channel Model Varying channel quality leads to varying optimal packet length (physical layer) –SNR  vs. optimal packet length where h is the overhead length Packet-length-based FSMC Channel Model

8. Packet-length-based Channel Model

9. Where is Free Space? Different channel state should have different fragmentation threshold FT (MAC layer) Maximum packet size at network layer –Overhead for transmitting c Mbit data

10. Where is Free Space?

11. How to Use the Free Space? Multiplicative relationship between the fragmentation threshold (FT) and FT m, i.e., the frame length for state i satisfies FT i =g i  FT m, where g i is a positive integer, i> m. b-MSDUs (basic MSDUs, the basic unit) whose length agrees with the FT m. Piggybacking rules. Share the same next hop.

12. How to Use the Free Space?

13. Piggybacking Rules Rule 1: favors the high priority packet –Piggyback the packets from the highest priority queue with non-empty buffer Rule 2: favors the low priority packet –Piggyback the packets from the lowest priority queue with non-empty buffer Other rules are possible

14. Remarks Comparison with rate adaptation (RA) –Fairness issue can only addressed at packet level while CP may be addressed in MAC segmentation level –RA may need to contend while CP may reduce contention overhead –CP does not affect QoS of the current priority queue which gives the courtesy while helping others

15. Analytical results A queue model for piggybacking N priority levels: P 0 P 1 …P N-1, where P 0 is the lowest priority Poisson arrival process λ k FSMC channel with FT i =g i  FT m, where g i is a positive integer, i> m. PK max =FT m Consider piggybacking only at one node with all the data destined to the same next hop

16. Analytical results Multiple server queue system with non- preemptive priority and FIFO discipline SR 0 operates in all states with service time Service rate is channel dependent SR 1 operates in states i(>m) with service time No-CP probability:

17. Analytical results Simple case: two channel states FT 1 = 2*FT 2. M/D/2 non-preemptive priority queue system –SR 0 operates in all states with service time –SR 1 operates in state S 1 with service time –Non-CP probability: π 0 Average waiting time Upper bound: –no piggybacking, only SR 0 works, unaware of the channel state, then M/D/1 priority queue system gives

18. Analytical results Lower bound: –Piggybacking is used with rule favoring high priority packets –Channel state is always S 1 ; both SR 0 and SR 1 work. – M/D/2 priority queue system gives Simulation results for = 0.01s with three different channel settings –π 0 =0.75, π 1 =0.25; –π 0 =0.5, π 1 =0.5; –π 0 =0.25, π 1 =0.75

19. Analytical results Average waiting time of P 0 Average waiting time of P 1

20. Performance Evaluation Simulation setup –OPNET –FT 1 =2  FT 0, t 01 =t 10 =0.002, –50 nodes, 1500*300m 2, TR=250m, modified random waypoint mobility model. –Poisson arrival process. –2 priority levels with equal probabilities, P 0 (low) and P 1 (high)

21. Performance Evaluation –Four different cases Case 1: unaware of channel states Case 2: aware of channel state with dynamic transmission rate (rate adaptation) Case 3: piggybacking with rule1 Case 4: piggybacking with rule2 –Two metrics End-to-end delay Packet delivery ratio.

22. Performance Evaluation Simulation Results –Impact of traffic load

23. Performance Evaluation Impact of node mobility

24. Performance Evaluation

25. Conclusions CP is capable of alleviating the conflict between throughput and fairness. –Utilizes the time-varying channel quality and changing traffic conditions. –Shortens the end-to-end delay and improves packet delivery ratio for all service priorities. –flexibly allocates the bandwidth among different types of traffic. Easy to be implemented in a distributed fashion. Applicable in networks using either reservation- based or contention-based MAC protocols.

26. Acknowledgement U.S. Office of Naval Research U.S. National Science Foundation

27. Question