Tham khảo tài liệu 'routing and wavelength assignment in optical wdm networks phần 2', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | If a request for a lightpath cannot be accepted because of lack of resources it is blocked. Because of the real-time nature of the problem RWA algorithms in a dynamic traffic environment must be very simple. Since combined routing and wavelength assignment is a hard problem a typical approach to designing efficient algorithms is to decouple the problem into two separate subproblems the routing problem and the wavelength assignment problem. Consequently most dynamic RWA algorithms for wavelength routed networks consist of the following general steps 1. Compute a number of candidate physical paths for each source-destination edge node pair and arrange them in a path list. 2. Order all wavelengths in a wavelength list. 3. Starting with the path and wavelength at the top of the corresponding list search for a feasible path and wavelength for the requested lightpath. The specffic nature of a dynamic RWA algorithm is determined by the number of candidate paths and how they are computed the order in which paths and wavelengths are listed and the order in which the path and wavelength lists are accessed. Let us Erst discuss the routing subproblem. If a static algorithm is used the paths are computed and ordered independently of the network state. With an adaptive algorithm on the other hand the paths computed and their order may vary according to the current state of the network. A static algorithm is executed off-line and the computed paths are stored for later use resulting in low latency during lightpath establishment. Adaptive algorithms are executed at the time a lightpath request arrives and require network nodes to exchange information regarding the network state. Lightpath set up delay may also increase but in general adaptive algorithms improve network performance. The number of path choices for establishing an optical connection is another important parameter. A fixed routing algorithm is a static algorithm in which every source-destination edge node pair is .
