1. 1 Minimum Interference Algorithm for Integrated Topology Control and Routing in Wireless Optical Backbone Networks Fangting Sun Mark Shayman University of Maryland, College Park {ftsun, shayman}@glue.umd.edu

2. 2 Introduction Advantages of free space optics Topology control The number of the transceivers is an important constraint in point-to-point wireless network In low mobility optical wireless backbone network, it is reasonable to setup bandwidth guaranteed paths

3. 3 System Assumptions Each node is either stationary or has low mobility Each node is equipped with a limited number point- to-point wireless interfaces A unidirectional wireless communication can be setup between a node and its potential neighbor No interference between transmissions Either –All network information is known to all nodes and routing path of an arriving request is computed at its source, or –Routes are computed at a centralized route server

4. 4 System Model Node Transformation: modeling interfaces Simple Example: modeling potential links

5. 5 Modeling Actual Links Request 1  2 with demand r is routed on the network or Another request 1  4 with demand q Forming new link consumes interfaces; routing through existing link consumes BW.

6. 6 Minimum Interference Routing References –K. Kar, M. Kodialam and T. Lakshman, JSAC, 2000. –I. Iliadis and D. Bauer, Networking 2002, LNCS 2345. Network with fixed topology Requests for BW guaranteed paths arrive randomly with no information about future requests Request is routed so as to minimize interference it may cause for routing of future requests –Links are weighted according to their potential importance for future requests –Minimum weight path is chosen to route current request Our main contribution: Extend to integrated topology control and routing by introducing notion of interface interference

7. 7 K-WSP under bottleneck and interface elimination Select a WSP between pair (s, d) – L p sd 1 is the set of links constituting this WSP btl sd 1 is the corresponding bandwidth – L b sd 1 is the subset of links whose residual bandwidth is btl sd 1 – I b sd 1 is the subset of interface links in L p sd 1 Select second WSP for (s, d) after L b sd 1 and I b sd 1 are removed Repeat this procedure until either K WSPs are found or no more WSP is available

8. 8 Critical link and critical interface Once used, the chance that some future requests can be satisfied decreases dramatically Compute the critical weight for each link and interface using K-WSP under bottleneck and interface elimination procedure –i th WSP is more important than the (i+1) th WSP –A link with less residual bandwidth is more critical, r(l) is the residual bandwidth of link l –A free interface on a node with fewer free interfaces is more critical, o(l) is the number of free interfaces of l’s owner node –Basic weight for general links and the interface links is different, w B is the basic weight for general links and w I is for interface links –Different ingress-egress pair has different importance, a sd is used to reflect the relative importance

9. 9 Critical link and critical interface, cont. Weight function –General links –Interface links (1) (2) Novel feature: putting weights on interfaces to model the interference that setting up a link causes for future links that may be needed.

10. 10 Integrated Algorithm Input: –Transformed network graph G( N, E ); –Set B indicating the residual bandwidth for each link; –Set I indicating the interface usage situation; –Set P of ingress-egress pairs; –A setup request (s k, d k, b k ) Output –Path between s k and d k with b k units or none. Procedure –Assign weight w(l) for each link according to equation (1) and (2) using previous procedure –Eliminate the links whose residual bandwidth is smaller than b k –Use Dijkstra’s algorithm to compute min-weighted path R –If R exists, reserve bandwidth and update sets E, B and I

11. 11 Simulation Setup Node number: 100 Moving range: 1000 x 1000 Interface constraint: 4 transmitters and 4 receivers per node Transmission range: 150 (network 1) and 175 (network 2) Ingress-egress pair number per set: 50 Bandwidth demand per request: uniform(1, 3) Initial bandwidth: 1000 (static case) and 20 (dynamic case) Dynamic case –Requests arrival process between each ingress-egress pair: Poisson –Requests holding time: exponentially distributed

12. 12 Performance Studies Static Case: Once a request is routed, it never leaves the network Percentage of rejected request over 10 rounds SMIRA_ISMIRAWSPSP Network 1 3.425.945.246.46 Network 2 2.728.934.675.42 For each network, 10 rounds of simulations are performed. Each round uses different ingress-egress pairs set, and to each pairs set 10 different request sequences (5000 requests per sequence for net 1 and 10000 requests per sequence for net 2) are computed to get average.

13. 13 Performance Studies, cont. Dynamic Case: A routed request will leave the network after some holding time Percentage of rejected requests over 10 rounds SMIRA_ISMIRAWSPSP Network 1 31.933.635.134.7 Network 2 9.914.613.613.8 For each network, 10 rounds of simulations are performed. Each round uses different ingress-egress pairs set, and to each pairs set 10 different request sequences (10000 requests per sequence) are computed to get average.

14. 14 Conclusion An algorithm for integrated topology control and routing in wireless optical backbone networks is developed The performance of proposed algorithm is superior to existing alternatives