“For the dynamic problem, instead of attempting to minimize the number of wavelengths as in the static case, we assume that the number of wavelengths is fixed (this is the practical situation), and we attempt to minimize connection blocking.”
Random Wavelength Assignment (R). First, all wavelengths are analyzed for availability in the total route. Among the available wavelength on the required route, one is assigned randomly.
First-Fit (FF). All wavelengths are numbered, a lower number wavelength is analyzed for availability in the given route. Smaller computation cost than the previous model. No global knowledge is required.
Least-Used (LU)/SPREAD. The wavelength that is the least used in the network is selected. The aim is to balance the load among wavelengths. Global information and therefore this model results in additional storage, communication overhead and computation cost.
Most-Used (MU)/PACK. The wavelength that is the most used in the network is selected. Similar storage, communication overhead and computation cost as LU. Outperforms FF and LU as optimized the use of wavelengths.
Min-Product (MP). Is used in multi-fiber networks. The goal of MP is to pack wavelengths into fibers, thereby minimizing the number of fibers in the network.
Least-Loaded (LL). Is used in multi-fiber networks. Select the wavelength with the largest residual capacity in the most-loaded link along route p. Outperforms MU and FF in terms of blocking probability.
By taking the network state into consideration, maxsum(MS) and relative capacity loss (RCL) try to establish the new call on a wavelength which has the least influence on the whole network. Although RCL is better in performance the knowledge of the updated topology makes it expensive and complex to implement.
MAX-SUM (MΣ). May be used in multi or single fiber networks. It assumes all connection requests are known in advance and route for each connection is pre-selected (global information: traffic matrix and the network state and topology are required). A wavelength is selected in the most congested link
Before lightpath establishment, the route is pre-selected; After lightpath establishment, it attemps to maximize the remaining path capacity.From all the possible paths MΣ considers all possible paths (lightpaths with their preselected routes) in the network and attempts to maximize the remaining path capacities after lightpath establishment.
Relative Capacity Loss (RCL). RCL calculates the Relative Capacity Loss for each path on each available wavelength and thcn chooses the wavelength that minimizes the sum of the relative capacity loss on all the paths. Similar to MΣ. can also be viewed as an approach that chooses the wavelength j that minimizes the capacity loss on all lightpaths.
Considering that longer light-paths have a higher probability of getting blocked than shorter paths, the wavelength reservation (Rsv) and protecting threshold (Thr) schemes attempt to protect longer paths. They can not work alone and must be combined with other wavelength-assignment schemes.
Wavelength Reservation (Rsv). A wavelength on a specified link is reserved for a traffic stream between 2 nodes, usually a multi-hop stream. Another connection request for that link cannot be assigned to the reserved wavelength even if it is idle. Reduces the blocking for multi-hop traffic, while increasing the blocking for single-hop traffic.
Protecting Threshold (Thr). A wavelength is assigned to a single-hop connection only if the number of idle wavelengths on the link is at or above a given threshold. One issue when applying these heuristics to the static problem is how to order the light-paths when assigning wavelengths.
Zang, H.; Jue, J. & Mukherjee, B. (2000), 'A review of routing and wavelength assignment approaches for wavelength-routed optical WDM networks', Optical Networks Magazine 1(1), 47—60.
R. A. Barry and S. Subramaniam, “The MAX-SUM wavelength assignment algorithm for WDM ring networks,” in Digest of Optical Fiber Communications Conference, Vol. 6 of 1997 Technical Digest Series (Optical Society of America, 1997), pp. 121–122.
X. Zhang and C. Qiao, “Wavelength assignment for dynamic traffic in multi-fiber WDM networks,” in Proceedings of the Seventh International Conference on Computer Communications and Networks, Vol. 1 (IEEE, 1998), pp. 479–485.
