Processing high-speed traffic in the electrical domain requires very high speed electrical interfaces and very high speed processors, which are expensive and consume a lot of energy. Researchers have long ago pointed out that a substantial part of the traffic that crosses internal nodes in core networks can be optically switched without requiring any kind of electrical processing in order to soften the burden of the electrical part of the nodes. The introduction of colorless (any add/drop port can serve any wavelength) and non-directional (any add/drop port can be routed to any direction) reconfigurable optical add-drop multiplexers (ROADM) allow to bypass optically the through-traffic in intermediate nodes, reducing the bits that have to be electronically processed in each node. However, optical signal degradation accumulates with the propagation distance and eventually the optical signal must be electrically regenerated in order to reach its destination with an acceptable signal quality. This requires the use of expensive optical regenerators. Finding ways to place these regenerators wisely has been a difficult problem to address due to the size of optical transport networks and the traffic dynamics. Most operators have been placing these regenerators on-demand, i.e. installing a regenerator only when a circuit needs it. However, this practice requires technician intervention in the field, in order to setup circuits that require regeneration, leading to longer service deployment and restoration. In addition, in the long run this approach tends to overprovision the network with regenerators increasing the overall cost.
In this paper the authors address the problem of finding the optimum places to pre-deploy regenerators. They formulate the problem and show that it is a NP-hard problem. However, they develop an efficient heuristic that takes into account both the cost of individual circuits (regenerator cost and transmission line system cost) and the number of regenerator sites. By applying this heuristic to a set of real networks they show through simulation that the developed heuristic leads to near-optimal results under most studied scenarios and cost models. They also extend the heuristic in order to consider the probability demand for each circuit. The developed algorithm is quite generic allowing various objective functions. The authors present a detailed description of the algorithm and analyze the various parameters involved. The algorithm is validated for a small network with an Integer Linear Programming (ILP) formulation.
In summary, the authors have developed a novel heuristic to pre-deployment of regenerators in practical networks. Unlike most of previous research work on regenerator placement, the authors pursue a holistic approach of minimizing overall network cost. The authors also show that with a small additional number of regenerator sites it is possible to allow survivable connections between most node-pairs in practical optical transport networks.
11/27/2013 3:10 AM
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