# Instantaneous Networking Service Availability for Disaster Recovery
## 2 Related Work
### Study of Statistical Communication Features, System Availability, and Reliability  
[PERSON] et al. [11] investigated the statistical properties of communication networks that support phone calls and text messages. Based on the introduction of geographical home location, the study shows that the probability that two customers communicate with each other over the network decreases with the distance between the customers, following a gravity model [23].  
It is observed that residents in the disaster situation tend to gather at the designated places such as shelters or evacuation centers [12]. [PERSON] et al. [13] examined the relationship between evacuation population size, emergency shelter capacity, and evacuation time. The proposed model was considered to facilitate decision-making on the position of emergency shelters and the allocation of evacuees to the shelters.  
The availability of a communication system can be generally measured by mean time between failures (MTBF) and mean time to repair (MTTR). The availability can be computed as \(A=MTBF/(MTBF+MTTR)\). [PERSON] et al. [9] studied the reliability of the data center. For a large system such as a data center, an entity or component instead of the whole system may have failures. The MTBF- and MTTR-based availability measurement can apply to measure the availability of a component or entirety of a system.  
[PERSON] et al. [8] introduced the reliability of communication pairs in IEEE 802.16-based mesh networks. It is shown that selecting a reliable path by avoiding poor links is important for the network to achieve higher data rate and low bit error rate (BER).  
[PERSON] et al. [24] introduced a resource allocation scheme in order to ensure the good communication quality in terms of latency and packet delivery ratio. The network resources include data mules and communication towers. The basic idea involves that each shelter is served by at least one network resource and involves trying to minimize the end-to-end network latency between the volunteer and control station. The proposed scheme increases the packet delivery ratio and reduces the communication latency compared with the resource-unplanned system.  
[PERSON] [25] showed the results that the fixed telephone system did not have a good performance in terms of service connectivity under a large earthquake situation. However, social networking service (SNS) communication via mobile phone had high connectivity performance, since the control for packet communication was independent with that of voice communication.  
In summary, a number of studies have addressed the communication systems and information sharing systems that support the capability of disaster resilience. However, few of the previous studies explicitly addressed the effectiveness of prompt and partial recovery of networking services and the speed of network restoration in the disaster situation according the communication features and population distribution. Moreover, it is difficult to utilize the conventional metrics on system availability and reliability to assess the effectiveness of temporary and partial recovery of networking services. Considering communication and population distribution in a disaster situation, local and partial recovery of networking services should also facilitate communication among users. This paper explicitly addresses the effectiveness of user service restoration procedure before the network is fully recovered, and examines the instant availability of networking service in a disaster situation. We evaluate the instant availability of networking service based on a local cloud system that enables the joint provision of communication support and information support for users in the disaster situation.