RWA and p-Cycles

While there has been many studies on the efficient design of p-cycles focusing on optimizing their spare capacity efficiency, few of them consider such a design under the wavelength continuity assumption, i.e., no wavelength converter at any node. Consequently, few authors look at the routing and wavelength assignment in the context of p-cycles, where p-cycles have to be assigned the same wavelength as the paths of which they protect at least one link. In this paper, we propose to investigate thoroughly the issue of wavelength conversion vs. wavelength continuity for p-cycles, with large scale optimization tools (decomposition techniques) in order to get an exact estimate of the consequences of the wavelength continuity assumption on the spare capacity requirements and on the provisioning cost. The recourse to decomposition techniques allows the design of exact efficient scalable models contrarily to heuristics which ensure scalability but no accuracy guarantee. In particular, it allows an on-line generation of improving p-cycles, one after the other with respect to the objective, instead of a costly computing time off-line generation of p-cycles as in previous studies, a key issue for a scalable solution. Numerical results show that the difference between the capacity requirement under wavelength conversion vs. under wavelength continuity is meaningless. Consequently, in view of the reduced provisioning cost (saving at least on the converters), we advocate the design of p-cycles under a wavelength continuity assumption.