## 1 Introduction  
The traditional sensor network is composed of a large number of densely deployed sensor nodes with short range radio and several sink nodes, and sensors in the network collaborate together to collect the target data and transmit them to the sink nodes. This approach, however, may not work effectively in scenarios with extremely low and/or intermittent connectivity due to sparse network density, obstacles, sensor node mobility or sensor energy exhaustion and so on. For example, in wild animal studies, researchers often install static sensors at some watering places and drive vehicles as mobile nodes to visit these disjoint sensors for data collection as a cost-efficient solution. Accordingly, the delay tolerant sensor network (DTSN) has been recently proposed. DTSNs belong to the general category of Delay Tolerant Networks (DTNs) [1], that is, networks will incur delays that can be very large and unpredictable. A DTSN is characterized by sensor nodes' intermittent connectivity. That is, it is difficult to form a well connected end-to-end path for all the sensor nodes to transmit data in the network.  
The publish/subscribe system is used to connect the distributed information providers and consumers in an asynchronous way, where there are subscribers, publishers and brokers [2]. The subscribers show their interest in certain events by submitting predefined subscriptions; the publishers issue newly detected events to the system; the brokers, which are generally custom servers, collect those subscriptions and events, match them and notify the subscribers of the matched events. In this way, the system supports loosely coupled interactions, such as activity monitoring systems.  
Much research has been done in the context of designing Pub/Sub systems in wireless networks [3, 4], where the authors all assume that the backbone network is still wired and connective. However, since a DTSN is quite different from the traditional wireless sensor network due to the particular sensor node characteristics, i.e., intermittent connectivity and limited energy, those previous Pub/Sub communication solutions are not suitable for DTSNs, and how to extend Pub/Sub systems in DTSNs is a challenge.  
In this paper, we propose a community-based event delivery protocol (CED) that adapts Pub/Sub systems to DTSNs. In our design, event delivery is based on several unchanged communities, which are formed by sensors in the network according to their connectivity. CED consists of two components for event delivery and queue management. In event delivery, events in a community are delivered to mobile subscribers once a subscriber comes into the community, for improving the data delivery ratio. The queue management employs both the event successful delivery time and the event survival time to decide whether the event should be transmitted or dropped for minimizing the transmission overhead. We evaluate the performance of the proposed approach by doing simulation and comparing it with the direct gathering protocol (DG). Simulation results show that our approach achieves a higher data delivery ratio with the lower transmission overhead and delivery delay than DG. To our best knowledge, our design is the first solution for DTSN, in the sense that it is the first attempt to apply communities in Pub/Sub systems for DTSN and use subscriber mobility prediction to support continuous event delivery in Pub/Sub systems.  
Our design addresses the following questions: (1) how to divide the network into several communities? (2) How to implement event delivery based on the constructed communities? (3) Why and how to design the event queue management scheme?The rest of the paper is organized as follows. Section 2 provides an overview of related work, while Section 3 presents the mobility model and basic assumptions. In Section 4, we introduce CED step by step. Section 5 shows the effectiveness of CED via simulation. Finally, Section 6 concludes the paper.