Trading network management complexity for blocking probability when placing optical regenerators

Optical signal regenerators (3R) are required to overcome the adverse effect of fiber and other transmission impairments. 3R units may be placed either at every node (full placement) or at some selected nodes (sparse placement) of the optical network. It has been argued [1] that while the latter placement strategy may not be optimal in terms of the total number of 3R units required to support a given set of static traffic demands, it offers a number of practical advantages over the former, e.g., a contained complexity of network management in terms of signaling overhead. In this paper the full and sparse placement strategies are compared in a dynamic optical network, whereby lightpaths are set up and torn down to best fit the offered changing demands. The study shows that the blocking probability due to the lack of available 3R units achieved by the sparse placement strategy may be comparable to the one achieved by the full placement strategy. Surprisingly, it may even be lower in some cases, thus providing an additional motivation in favor of the sparse placement strategy. The study also shows that the algorithm used to choose the nodes where to place the 3R units must be designed carefully. Two placement algorithms are compared, reporting differences in signaling overhead level as high as 6 times (when achieving a desired level of lightpath connectivity) and differences in blocking probabilities as high as two orders of magnitude (when using the same level of signaling overhead).