1. A Dynamically Adaptive Hybrid Algorithm for Scheduling Lightpaths in Lambda-Grids Neena R. Kaushik and Silvia M. Figueira Santa Clara University Presented by Yang-suk Kee

2. Outline Background Lightpath Scheduling Experiments Conclusion

3. Background Advance reservation Guarantees that resources will be available at a pre- determined time to participate in the execution of a Grid application Lambda Grid Lightpath A wavelength data channel liking multiple optical segments A single wavelength through the path Different wavelength with wavelength conversion Data-intensive grid application Multiple paths

4. Problem Definition Advance reservation of multiple lightpaths How to schedule multiple lightpaths requested by advance reservation over optical network with no converter? B D C A Source Destination

5. Lightpath Scheduling Skeleton Step1: determines edge-disjoint paths Step2: determines wavelengths for paths Edge-disjoint path nth edge-disjoint path A path that does not share any of its edges with the previous n-1 edge-disjoint paths 1 st edge-disjoint path is the shortest path Algorithm Repeat Dijkstra’s shortest path algorithm by removing the edges that were part of the shortest paths.

6. Lightpath Scheduling Schemes Spreading Balances the wavelength assignment throughout the available edge-disjoint paths Packing Concentrates the wavelength assignment in the shortest path first followed by the alternate edge-disjoint paths SpreadingPacking B D C A B D C A A->C (4)

7. Wavelength-Balancing Algorithm Begin For i = 1 to number of wavelengths For j = 1 to number of edge-disjoint paths If wavelength[i] is available for all segments in edge-disjoint path[j] Allocate wavelength[i] for all segments in edge-disjoint path[j] If all requests of user are satisfied Print success Else Print the number of requests satisfied and number denied End

8. Wavelength-Concentrating Algorithm Begin For i = 1 to number of edge-disjoint paths For j = 1 to number of wavelengths If wavelength[j] is available for all segments in edge-disjoint path[i] Allocate wavelength[j] for all segments in edge-disjoint path[i] If all requests of user are satisfied Print success Else Print the number of requests satisfied and number denied End

9. Scheduling Comparison BalancingConcentrating B D C A A->C (4), B->D (4), A->B (1), B->D (2) Four wavelengths per link B D C A (x)

10. Blocking Probability Requests for 1-hop lightpaths in a 32-node ring: uniform requests Requests for 8-hop lightpaths in a 32-node ring with chords: cons tant requests.

11. Lessons From the experiments using simple topologies Partial mesh/ring/ring with spike/ring with chord Balancing algorithm has similar or better blocking probability than concentrating one in most cases Concentrating algorithm is better With short hop (1-hop) Shorter time slots provide lower blocking probability => Hybrid algorithm of balancing and concentrating

12. Hybrid Algorithm of Balancing and Concentrating begin firstpass = 1; while (firstpass is not equal to 3) for i = 1 to number of wavelengths for j = 1 to number of edge-disjoint paths if first pass is equal to 1 and edge-disjoint path has more than x-hops Continue … check if it satisfies balance algorithm end (for edge-disjoint paths loop) end (for number of wavelengths loop) Increment firstpass by 1 end (while loop) return the number of requests satisfied end

13. Experimental Setup Metric of quality Blocking probability (denial rate) Simulation-based FONTS (Flexible Optical Network Traffic Simulator) Generates on-demand and advance reservation requests Uses Stochastic models LRSS (Lightpath Request Scheduling Simulator) Simulates scheduling algorithms Takes as input the network topology and a trace of requests for ligthpaths (from FONTS)

14. FONTS (Flexible Optical Network Traffic Simulator) Request arrival time Poisson distribution Source node/Destination node Constant/uniform/arbitrary probability Size of data to transfer (Tera bytes) Constant/uniform/arbitrary probability/heavy-tailed Number of lightpaths requested Constant/uniform/heavy-tailed Advance reservation start time Poisson distribution Number of time slots Constant/variable

15. Simple Topology Requests for 1-hop lightpaths in a 32-node ring: uniform requests All schemes except balancing are identical Requests for 8-hop lightpaths in a 32-node ring with chords: cons tant requests. 161718 2024

16. National Lambda Rail National Lambda Rail: Constant R equests

17. Conclusion & Discussion Conclusion Provides simulation tools for lightpath scheduling Quality of scheduling algorithms depends on traffic characteristics Hybrid scheduling achieved lower blocking probability Discussion Blocking probability represents network utilization properly? This hybrid algorithm is close to balancing algorithm except the case of ring topology. Need more study about the degree of nodes, length of hops, and network utilization