1 Dynamic RWA Connection requests arrive sequentially. Setup a lightpath when a connection request arrives and teardown the lightpath when a connection departs Goal is to minimize connection blocking Solve the routing subproblem and the wavelength assignment subproblem separately

2 Routing Fixed routing Fixed-alternate routing Adaptive routing

3 Fixed Routing Always choose the same fixed route (calculated offline) for a given source- destination pair –E.g. shortest-path routing Advantage: simple Disadvantages: –High connection blocking –Unable to handle faults

4 Fixed-Alternate Routing Each node maintains an ordered list of a fixed set of routes to each destination node –E.g., k shortest-path routes Primary route: the first route in the list Alternate route: a route that does not share any links with the first route –Useful for fault tolerance

5 Fixed-Alternate Routing When a connection request arrives, the source node tries each of the routes in the list in sequence until a route with a valid wavelength assignment is found Advantages –Simple –Fault tolerance –Significantly reduce the connection blocking probability compared to fixed routing

6 Adaptive Routing Route is chosen based on the current network state Two approaches –Adaptive shortest-cost-path routing –Least-congested-path routing

7 Adaptive Shortest-Cost-Path Routing Use layered graph Link costs –1 for unused link –  for used link –c for wavelength conversion link When a connection request arrives, compute the shortest-cost path between source and destination Advantage: low blocking Disadvantage: nodes need update network state whenever a connection is setup/teardown

8 Least-Congested-Path (LCP) Routing For each s-d pair, a set of routes is predetermined When a connection request arrives, the least- congested path is chosen –Congestion on a link = # wavelengths available on the link Fewer available wavelength  more congested –Congestion on a path = congestion on the most congested link in the path Use shortest-path routing to break ties An alternative: give priority to shortest paths, use LCP to break ties

9 Wavelength Assignment Heuristics Assume fixed number of wavelengths Minimize overall blocking probability for all connection requests –Single-fiber networks: R, FF, LU, MU –Multi-fiber networks: MP, LL, M , RCL Protect multihop connections to achieve greater degree of fairness –Rsv, Thr

10 Wavelength Assignment Heuristics: Single-Fiber Case Random Wavelength Assignment (R): –Find all wavelengths available on the required route –Randomly choose one available wavelength First-Fit (FF) –Wavelengths are numbered –Choose the first available wavelength –Computation cost lower than R –Perform well in terms of blocking probability and fairness Both R and FF require no global knowledge

11 Wavelength Assignment Heuristics: Single-Fiber Case Least-Used (LU)/SPREAD –Choose the least used wavelength –Attempt to balance the load among all wavelengths –Favor short paths, not fair for long paths –Perform worse than random Most-Used (MU)/PACK –Choose the most used wavelength –Pack connections into fewer wavelengths –Slightly outperform FF Both LU and MU require global knowledge

12 Wavelength Assignment Heuristics: Multi-Fiber Case Min-Product (MP) –Goal: minimize # fibers by packing wavelengths into fibers –First compute for each wavelength j that is available on p –Choose the lowest numbered wavelength in the set of wavelengths that minimize the above value –Become FF in single-fiber networks –Perform worse than the multi-fiber version of FF (both fibers and wavelengths are ordered)

13 Wavelength Assignment Heuristics: Multi-Fiber Case Least-Loaded (LL) –Select the wavelength that has the largest residue capacity on the most loaded link along route p –Choose the minimum indexed wavelength j in S p that achieves –Become FF in single-fiber networks –Outperform MU and FF

14 Wavelength Assignment Heuristics: Multi-Fiber Case MAX-SUM (M  ) –Assume the set of possible connection requests is known in advance and the route for each connection is pre-selected –Attempt to maximize the remaining path capacities after lightpath establishment

15 Wavelength Assignment Heuristics: Multi-Fiber Case MAX-SUM (M  ) –  : a network state that specifies the routes and wavelength assignments of existing lightpaths –Link capacity r( , l, j) on link l and wavelength j in state  : # fibers on which wavelength j is unused on link l –Path capacity r( , p, j) on path p and wavelength j: # fibers on which wavelength j is available on the most congested link along path p –Path capacity of path p in state , R( , p): sum of path capacities on all wavelengths

16 Wavelength Assignment Heuristics: Multi-Fiber Case MAX-SUM (M  ) –  ’(j): the next state of the network if j is assigned to the connection –P: set of all potential paths for connection requests in the current state –Choose the wavelength j that maximizes –Equivalently, choose wavelength j that minimizes the total capacity loss on this wavelength, which is

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19 Wavelength Assignment Heuristics: Multi-Fiber Case Relative Capacity Loss (RCL) –Improve on M  by taking into consideration # available alternate wavelengths for each potential future connection –RCL chooses wavelength j that minimizes the sum of the relative capacity loss on all the paths

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21 Heuristics for Protecting Multihop Paths Longer lightpaths have a higher probability of getting blocked than shorter paths  want protect longer paths Proposed schemes: Rsv and Thr –Only specify whether the connection request can be assigned a wavelength under the current wavelength- usage conditions  must be combined with other wavelength assignment schemes –Achieve a greater degree of fairness

22 Heuristics for Protecting Multihop Paths Wavelength Reservation (Rsv) –A given wavelength on a specified link is reserved for a multihop traffic stream –Reduce blocking for multihop traffic while increasing the blocking for single-hop traffic Protecting Threshold (Thr) –A single-hop connection is assigned a wavelength only if the number of idle wavelengths on the link is at or above a given threshold.