## 1 Introduction  
In recent years, there is a growing concern in society about the possibilities of earthquakes whose epicenters are directly below a major city. In the event of such a disaster, mobile terminals can be an effective means of communication but mobile communication networks are likely to be damaged. In fact, in the aftermath of the Great East Japan Earthquake, base stations were destroyed or damaged, and it took about one month before they were fully restored [1, 2]  
A type of network that is being studied to secure a communication infrastructure in the event of a disaster is a delay/disruption tolerant networks (DTN) [3]. Based on near-field communication and store-and-carry data transfer, the DTN makes data transfer possible, even in inferior communication conditions, such as frequent disruptions or disconnections of communications and large transmission delays. However, the DTN still has many issues to be solved, such as how to improve the delivery rate (rate at which messages reach their destinations) and how to reduce battery consumption of mobile terminals. Representative protocols used in DTN are _Epidemic Routing_ and _Spray and Wait_. In _Epidemic Routing_, which is also known as infectious routing, a terminal that has data sends its copy to all the terminals to which it is connected. Advantages of this routing are that the delivery rate is relatively high and that the delay time is short. However, it has a problem of generating large traffic loads and consuming battery charge greatly. _Spray and Wait_ allows a trade-off between data transfer delay and storage usage in relay nodes by adjusting the upper bound on the number of copies that can be made per message. However, a problem with _Spray and Wait_ is that it is difficult to determine the appropriate upper bound in the aftermath of a disaster.  
Our study focuses on using DTN to collect information about the safety of victims in a disaster area while mobile communication services are disrupted. The DTN consists of mobile terminals of victims and mobile terminals of information carriers, and shelter terminals. We propose using a bundle layer protocol that is based on a receiver-triggered handshake protocol. This protocol is intended to avoid network congestion, and reduce battery consumption and storage usage of mobile terminals by limiting the number of bundles that are generated. It has been implemented on a network simulator to build an evaluation environment. The disaster area has been modeled on an area around Shinjuku Station in Tokyo. Victims are randomly distributed in the disaster area. We have compared the proposed protocol with _Epidemic Routing_ and _Spray and Wait_ in terms of the delivery rate, and delivery time (the length of time taken for messages to reach their destinations). We have found that the delivery rate of the three methods are, more or less, the same, but that the proposed method is superior to the other two methods in terms of storage usage and battery consumption of terminals, and the number of bundles generated in the network. Section 2 summarizes related studies. Section 3 discusses the structure of DTN that will be formed after a disaster, implementation issues, and our performance objective for the DTN. Section 4 proposes a bundle layer protocol that is based on a receiver-triggered handshake protocol. Section 5 presents the simulation environment we have built to evaluate the proposed protocol as well as evaluation conditions. Section 6 discusses the evaluation results. Section 7 gives conclusions and future issues.