# Instantaneous Networking Service Availability for Disaster Recovery
###### Abstract  
Networking services may be broken down in a disaster situation while people in the disaster area(s) strongly demand networking services for both communication and information sharing among users. This requires the fast restoration of networking services to fulfil the demand-supply gap. Although there are a number of studies on restoring communication and networking in disasters, few studies have explicitly examined the service availability during the temporary and partial recovery process of network restoration. From the perspective of users in the disaster area, it is important to be able to communicate or share information with people whenever they want/need to do so. Therefore, partial and local recovery of the networking services also plays an important role for improving service availability in the disaster situations. To assess the restoration effectiveness of networking services with a measure of user satisfaction level, we propose to use instant networking service availability (I-NSA), a novel metric, and we examine the effectiveness of networking service restoration solutions using the metric. I-NSA allows us to clearly express the instant availability of networking services that drastically changes with the elapsed time from the disaster occurrence in disaster areas. This paper examines the effective improvement of I-NSA when Local-and-Instant Clouds (LI-Clouds) are applied to the disaster situation. LI-Cloud has been designed and practically developed to provide deployable networking services to users. We verify that LI-Cloud enables significant improvement on the I-NSA performance in the fast restoration of networking services. network restoration; service availability; resilience; Local-and-Instant Clouds +
Footnote †: journal: Applied  
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network system performance in emergencies. Mean time between failures (MTBF) and mean time to repair (MTTR) are major methods used to assess the availability [9]. For example, the availability can be evaluated as \(A=MTBF/(MTBF+MTTR)\). People in the disaster region strongly demand the prompt restoration of networking services, such as information sharing and communication support, due to the time limitation for the rescue. In the real disaster situation, however, some time is needed for network restoration because of its complex process. The disaster region usually consists of multiple service areas that need multiple local networks. The distance between areas may be long. Considering real recovery cases, time is needed for the deployment of the infrastructure of local networks and construction of links to the global network. Consequently, the restoration procedure of the user networking service is a time-dependent and multiphase procedure. The studies on network restoration have paid little attention to the restoration process from the time of deploying local communication service to the time of recovery of the whole communication service, including the global network connection. The restoration should be measured by the user-centric availability of networking service and the speed of the restoration procedure of user services. Conventional measurement of availability focuses on one system object--either the whole system or its components. On the other hand, the user-centric availability of networking service is a measure that involves the integrated availability of a set of network infrastructure nodes and links in the local areas. The network restoration system being examined in this study is Local-and-Instant Clouds (LI-Clouds), which enable prompt and conventional networking service restoration in the disaster environment even when there is no Internet connectivity [10].