1. Routing Performance in the Presence of Unidirectional Links in Multihop Wireless Networks Mahesh K. Marina and Samir R. DasACM MOBIHOC’02

2. Outline • Introduction • Benefit of unidirectional links for routing • Technical of handling unidirectional links in AODV • Performance evaluation • Conclusions

3. Introduction(1) • 3 reason cause unidirectional link • Difference in radio transceiver capabilities • Use of transmission range control • Difference in wireless channel interference experienced by different nodes

4. Introduction(2) • 2 conceivable advantages over using only bidirectional links • Improvement of the network connectivity • Better and shorter paths are provided

5. B communicates C directly C requires 2 hops to communicate with B Without unidirectional link, the graph will separate into two parts Introduction(3)

6. Introduction(4) • Many common link-layer protocols for medium access and address resolution • Assume bidirectional link • Depend on two-way handshakes and acknowledges • Ex: IEEE 802.11 DCF • RTS-CTS-DATA-ACK

7. Benefit of Unidirectional Links for Route(1) • 3 models for evaluation of unidirectional links • Two Power • Random Power • Rodoplu and Meng (R&M)

8. Benefit of Unidirectional Links for Route(2)

9. Benefit of Unidirectional Links for Route(3)

10. Benefit of Unidirectional Links for Route(4)

11. Benefit of Unidirectional Links for Route(5)

12. Forgoing Observation • Unidirectional links • Provide only incremental benefit • Do not improve connectivity in most cases • Improve shortest path cost in general • Provide small benefit with per-hop acknowledge under certain densities and radio ranges

13. RREQ RREP RREQ RREQ RREQ DISCARD RREP RREQ Technical of handling unidirectional links in AODV(1)

14. Technical of handling unidirectional links in AODV(2) • 3 techniques to handle unidirectional links in AODV • Black Listing • Hello • Reverse path Search

15. RREQ RREQ RREQ RREP RREQ RREQ RREQ RREQ RREP RREP RREQ RREP RREP RREQ RREQ RREP BRREP BRREP Technical of handling unidirectional links in AODV(3)

16. Performance Evaluation(1)

17. Performance Evaluation(2)

18. Performance Evaluation(3)

19. Conclusions • Reverse Path Search technique performs the best • IEEE 802.11 MAC performance degrades in the presence of unidirectional links • A new efficient MAC protocol to handle unidirectional links is needed