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Network survivability endeavors to ensure the uninterrupted provisioning of services by the network operators in case of a disaster event. Studies and news reports show that network failures caused by physical attacks and natural disasters have significant impacts on the optical networks. Such network failures may lead to a section of a network to cease to function, resulting in non-availability of services and may increase the congestion within the rest of the network. Therefore, fault tolerant and disaster-resilient optical networks have grasped the attention of the research community and have been a critical concern in network studies during the last decade. Several studies on protection and restoration techniques have been conducted to address the network component failures. This study reviews related previous research studies to critically discuss the issues regarding protection, restoration, cascading failures, disaster-based failures, and congestion-aware routing. We have also focused on the problem of simultaneous cascading failures (which may disturb the data traffic within a layer or disrupt the services at upper layers) along with their mitigating techniques, and disaster-aware network survivability. Since traffic floods and network congestion are pertinent problems, they have therefore been discussed in a separate section. In the end, we have highlighted some open issues in the disaster-resilient network survivability for research challenges and discussed them along with their possible solutions.

There has been a surge in ozone gas relevance in agriculture, environment and in the industry. This has resulted in increased research activities in areas involving ozone gas generation, application, safety and sensing. In this manuscript we present reviews of selected recent works (2011–2015) on ozone gas sensors based on absorption spectroscopy. Issues addressed include sensors applications versus requirements; sensors performance versus limitations and cost of sensors. Outstanding research issues are also outlined. While the review is mainly biased towards sensing of ozone using conventional absorption spectroscopy, other methods such as photo acoustic, photo reductive, photo stimulated, metal oxides, electrochemical, chemical, solid state and resistive ozone sensors were also considered in light of their performance criteria. Generally, it was observed that new applications of ozone gas lead to new sensing research challenges. Several sensing parameters were repeatedly investigated and improved upon over the years. Some of these parameters include: selectivity, sensitivity, speed of response, cost of sensor, lower detection limit and portability.