1. Virtual-Topology Adaptation for WDM Mesh Networks Under Dynamic Traffic

2. Outline Introduction General approach to the virtual-topology reconfiguration problem Formulation of Local Optimization (MILP formulation) Heuristic Adaptation Algorithm Performance of Heuristic Adaptation Algorithm Future Direction

3. Introduction Why and How to reconfigure the virtual- topology under dynamic traffic ? –A virtual-topology is a set of static lightpaths established to provide all optical connectivity between nodes for a given traffic demand –Hard to form a fully-connected virtual- topology

4. Example of Traffic Measurement

5. General approach to the virtual- topology reconfiguration problem

6. Two-phase operation First phase : virtual-topology design for the new traffic conditions –Future traffic demand is assumed to be known, but the traffic changes predicted may be inaccurate Second phase : transition period from the old virtual-topology to the newly designed one –During the transition period, the involved lightpaths can ’ t be used

7. Formulation of Local Optimization (MILP formulation)

8. MILP (mixed-integer linear program) Three actions –Addition of a lightpath –Deletion of a lightpath –No change to the virtual-topology

13. MILP (mixed-integer linear program) Since the time complexity of the MILP limits its use for large networks, we turn to heuristic method

14. Heuristic Adaptation Algorithm

15. Key Ideas As traffic fluctuates over time, it will be monitored systematically No other assumption will be made on future traffic pattern Small adjustments instead of waiting changing the topology entirely Only one lightpath change is allowed at the end of each observation period A center manager will collect the virtual-link usage information Use shortest-path routing and first-fit scheme One-phase reconfiguration algorithm

16. Quasi-balanced Topology The lightpath have the maximum load We choose to add a lightpath through, so the load will decrease to

17. Heuristic Adaptation Algorithm

20. Performance of Heuristic Adaptation Algorithm

21. Physical Topology 19 nodes 31 bidirectional links 16 wavelengths per fiber 8 transmitters and 8 receivers each node

25. Effect of Observation Period

27. Future Direction

28. How high and low watermarks can be changed dynamically ? Not only change one lightpath each step