Threshold based selective link restoration for optical WDM mesh networks

This paper studies the problem of providing failure recovery in optical wavelength division multiplexed (WDM) networks. One of the mechanisms widely studied is reactive link restoration, where recovery is provided by determining paths around a failed link after the failure occurrence. This is characterized by efficient resource utilization (since recovery capacity need not be reserved ahead of time), fast failure signaling rate and scalability. However, one of its main drawbacks is the inability to provide any guarantee of restoration. The restoration efficiency also reduces as the overall network load increases due to a reduced probability of finding a restoration route as a result of limited available spare capacity. In contrast, proactive protection mechanisms reserve backup capacity during connection setup. Here, resources may go unused if failures are not frequent thus leading to lower resource utilization. This paper proposes a hybrid protection-restoration mechanism, called threshold-based selective link restoration, that attempts to improve the overall restoration efficiency provided by link restoration. The proposed mechanism pro-actively reserves bandwidth similar to pre-planned protection, but only for a subset of the network links and at times of need as determined by a predefined policy. This paper considers two policies using which the threshold is determined: (i) per-link load and (ii) per-link reliability. The paper presents a detailed performance comparison of the proposed restoration mechanism with dynamic restoration and presents a study of the trade-off between network provisioning and restoration efficiency. The simulation results indicate that under high loads, the proposed mechanism maintains a consistent restoration efficiency of at least 10% or higher when compared to dynamic restoration.