Courtesy Piggybacking: Supporting Differentiated Services in Multihop Mobile Ad Hoc Networks

1. Courtesy Piggybacking: Supporting Differentiated Services in Multihop Mobile Ad Hoc Networks Wei Liu Xiang 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 trafficdynamics

4. Motivation • Piggybacking can relieve the conflict between different transportation. • A tunnel scenario ( the Whittier Tunnel in Alaska) • 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:solvingconflict 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 FTm, i.e., the frame length for state i satisfies FTi=giFTm, where gi is a positive integer, i> m. • b-MSDUs (basic MSDUs, the basic unit) whose length agrees with the FTm . • 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: P0 P1…PN-1, where P0 is thelowest priority • Poisson arrival process λk • FSMC channel with FTi=giFTm, where gi is a positive integer, i> m. • PKmax=FTm • 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 • Service rate is channel dependent • SR0 operates in all states with service time • SR1 operates in states i(>m) with service time • No-CP probability:

17. Analytical results • Simple case: two channel states FT1= 2*FT2. • M/D/2 non-preemptive priority queue system • SR0 operates in all states with service time • SR1 operates in state S1 with service time • Non-CP probability: π0 • Average waiting time • Upper bound: • no piggybacking, only SR0 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 S1; both SR0 and SR1 work. • M/D/2 priority queue system gives • Simulation results for = 0.01s with three different channel settings • π0=0.75, π1=0.25; • π0=0.5, π1=0.5; • π0=0.25, π1=0.75

19. Analytical results Average waiting time of P0 Average waiting time of P1

20. Performance Evaluation • Simulation setup • OPNET • FT1=2FT0 , t01=t10=0.002, • 50 nodes, 1500*300m2, TR=250m, modified random waypoint mobility model. • Poisson arrival process. • 2 priority levels with equal probabilities, P0(low) and P1(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