1. Logical Topology Design and Interface Assignment for Multi- Channel Wireless Mesh Networks A. Hamed Mohsenian Rad Vincent W.S. Wong The University of British Columbia, Vancouver, Canada Globecom 2006

2. Outline Introduction Proposed algorithm (TiMesh) Performance comparison Conclusion

3. Introduction Multi-channel wireless mesh network  Each mesh router is equipped with multiple network interface cards (NICs)  Each interface operates on a distinct frequency channel in the 802.11 a/b/g bands

4. Introduction Three important issues need to be addressed in MC-WMNs  Logical Topology Design  Interface Assignment  Channel Allocation

5. TiMesh Problem Formulation Bidirectional Constraint Channel Dependent Constraint Ripple Effect Constraint Total Flow on a Logical Link Flow Conservation at Each Node Hop Count Constraint Effective Capacity and Link Utilization Objective Function

6. Problem Formulation Logical Topology Physical Topology G(N,E) Each router has I network interface mn If I =3

7. Bidirectional Constraint 1 denote an I x 1 vector Assume the logical links are bidirectional The linear term is equal to 1 if node m assigns one interface to communicate with node n, and is equal to 0 otherwise There is a logical link between nodes m and n if both terms are equal to one mn 1 1 Logical Link

8. Channel Dependent Constraint n m k s r Upper bound Determines the number of additional logical Link share an interface with link (m,n) The lager the value of the summation, the smaller the proportion of time that each logical link can access the shared NIS

9. Ripple Effect Constraint

10. nm s r Ch 6

11. Total Flow on a logical link denote the average packet arrival rate

12. Flow Conservation at each node Hop count constraint Flow conservation at each node Hop count constraint Denote the minimum hop count between the source and destination in the physical topology

13. Effective capacity and Link utilization Capacity of the logical link Utilization of the logical link When the utilization is close to 1, the queuing delay tends to be lager

14. Objective Function

15. Performance Comparison Using NS-2 simulator Network field is 1000m * 800m 30 wireless mesh router 4 of them also serve as gateways (locate at corner) Each router is equipped with 3 NICs Communication and sensing/interference range are 250m and 450m 10 random physical topologies 40 data flows: half of them are internal flows and the others are external flows

16. Performance Comparison Compare with Hyacinth mechanism  Aggregated goodput  Average round-trip time  Packet delivery ratio  Average end-to-end delay

17. Aggregated goodput Total number of correctly received packets at the destinations

18. Average round-trip time Average time delay between sending a TCP segment and receiving its ack

19. Packet delivery ratio Total number of packets received by all destination to the total number of Packets transmitted by all sources

20. Average end-to-end delay The average time it takes for a packet to traverse the network from a source to a destination

21. Conclusions TiMesh MC-WMN architecture  The algorithm prevents ripple effect among channel dependent wireless logical links  The algorithm guarantees network connectivity, supports both internal traffic among the wireless routers and external to the Internet