1. Improving QoS Support in Mobile Ad Hoc Networks Agenda Motivations Proposed Framework Packet-level FEC Multipath Routing Simulation Results Conclusions

2. Motivations Challenges for improving QoS in MANET Network congestion, buffer overflow Same as we met in wired networks, but bandwidth is much lower Radio channel characteristics Multipath propagation, path loss, interference … Frequent topology reconfigurations Constant rerouting & packet dropping due to link/path failures

3. Motivations QoS provisioning in MANET requires QoS-based routing protocol, Medium Access Control (MAC) protocol, and resource reservation protocol to work together. This work focuses on improving QoS performance at the network layer, addressing packet losses due to link and path failures resulting from node mobility. Improve packet delivery ratio Improve end-to-end delay and jitter Maintain low control overhead Reduce bursty packet losses

4. Proposed Framework Multi-path routing protocol (MPR) Spatial reutilization of wireless channel Improve packet delivery ratio, end-to-end delay and jitter, routing overhead Reduce burstiness of packet losses Packet-level Forward Error Correction scheme Reduce average packet loss rate Avoid retransmission

5. Observations Packet-level FEC can reduce packet loss, avoid retransmission and associated delay. But, no significant gains can be attained by adopting packet-level FEC over single path routing in MANET. Packet loss tends to be bursty due to frequent path failures A packet interleaving scheme is needed. Delay -- packets need to be buffered for interleaving before being sent out. Memory requirements. Multi-path routing can also act as a packet interleaver.

6. Correlated Packet Loss in MANET

7. A 3x4 Packet Interleaver Input sequence: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] Output sequence: [1, 4, 7, 10, 2, 5, 8, 11, 3, 6, 9, 12] No impact on packet loss rate, but effectively reduces the average burst length, converting bursty losses to random losses.

8. Multi-path Illustration

9. Reed-Solomon Erasure Coding

10. Multipath Routing Scheme Dynamic Source Routing (DSR) is chosen as the basis protocol for MPR implementation. Major difference between MPR and DSR: Route Discovery: Target node replies indiscriminately to all incoming route requests carrying node-disjoint routes. Intermediate nodes no longer reply to route requests. Route Maintenance: New route discovery initiated only after all active routes broke. Packet Distribution: Round robin packet distribution over multiple routes. Up to 3 node-disjoint paths are concurrently in use.

11. Simulation Model All modifications were integrated directly into Qualnet. Random waypoint mobility model. 50 mobile nodes randomly placed in a terrain of dimension (1500, 1500). CBR traffic, 5 sessions, from 10, 11, 12, 13, 14 to 25, 26, 27, 28, 29, respectively. Each with 500 data packets of size 512 bytes. IEEE 802.11 MAC with RTS/CTS. Metrics: Packet delivery ratio, end-to-end delay and jitter, average routing overhead, burst length of packet loss.

12. Simulation Results: Comparison among MPR, SPR, MPR-FEC and SPR-FEC

16. Correlated Packet Loss Histogram (1)

17. Correlated Packet Loss Histogram (2)

18. Correlated Packet Loss Histogram (3)

19. Effects of Various FEC Redundancy Levels

21. Effects of Various FEC Block Sizes

23. Conclusions MPR significantly outperforms SPR in all criteria. SPR-FEC performs worse than SPR, due to inherent packet loss correlation in MANET. MPR reduces most consecutive packet losses to single packet losses, desirable by real-time video/audio applications. MPR-FEC further improves packet delivery ratio, but at the cost of higher delay, jitter and control overhead (compared to MPR). Higher FEC redundancy may not always be good.

24. Questions? Thanks! The End