We propose a two-step method to enhance the dual-failure restorability in p-cycle protected mesh networks that are optimally designed to withstand only single failures. Our two-step method relies on finding alternate routes to repair the non functional p-cycles upon the first failure and protect the exposed spans. We then compare our proposed method with the cycle reconfiguration method proposed in [9] in which the spare capacity is reconfigured dynamically (either incrementally or completely) after the first failure. We find out the additional spare capacity required for dual failure restorability as compared to single failure restorability for our proposed method as well as the incremental and complete cycle reconfiguration methods. We conclude our findings based on our results and discuss the advantages and disadvantages of each of these methods.

We study the unavailability of end-to-end traffic in p-cycle based mesh networks, which are designed to protect against single link failures. It has been shown earlier by Grover and Clouqueur that the p-cycle length as well as its topology play a vital role in determining the availability of span(s) which are protected by the p-cycle. Similarly, we derive the relationship between the unavailability of a span(s) and the topology of the p-cycles) which is allocated for the restoration of the span(s). Based on these insights and on the fact that the end-to-end unavailability of a working path depends not only on the length of the restoration path but also on the number of spans along the working path, we try to design a method for allocating p-cycles such that the end-to-end unavailability is bounded by an upper limit and the upper limit can be varied as desired. As expected, results show that more capacity is required to guarantee a lower end-to-end unavailability. Our results also show that shorter service paths tend to use longer p-cycles than longer service paths, to obtain the same level of availability; this is expected since the path length, apart from the p-cycle length, also plays a role in determining the availability of the service path. We compare this formulation with a formulation which rather limits the hop count of candidate p-cycles to provide a lower end-to-end unavailability. We notice that directly limiting the end-to-end unavailability, as proposed by this paper, gives better results in terms of spare capacity redundancy than limiting the hop count of p-cycles. That is because the former allows shorter working paths to use p-cycles with higher hop count and therefore a better utilization of the allocated spare capacity