## 1 Introduction  
Traditionally, the internet is formed primarily by connectivity homogeneous devices (i.e., computers). But, nowadays, there are several paradigms in networking such as mobile, grid and cloud computing, which enable a purposeful connectivity between various devices such as computers, smart-phones, tablets, cameras, etc. As a new paradigm for this vision, the Internet of Things (IoT) is introduced in the area of wireless communications and networking [1]. IoT refers to the emerging trend of expanding hand-held devices and physical objects with sensing, computing and communication capabilities, connecting them to form a network. The IoT research covers a wide range of areas, including object identification and tracking, object networking, sensing data visualization, privacy control, and so on. With the advent of IoT, the underlying networks play a more significant role for data transmission in IoT applications. However, many IoT applications just suffer from problems such as unreliable wireless, poor trust model and weak mobile networks. An IoT system in an urban environment is often characterized by a lack of connectivity, dynamic mobility and long links interruptions. These unstructured networks can be considered as a type of delay/disruption tolerant networks (DTN) [2; 3]. In some specific circumstances like InterPlaNetary internets, military ad-hoc networks, pocket switched networks, vehicular ad-hoc networks, mobile social networks and so forth, DTN has shown its high reliability since it owns the ability of data storage and transmission at each node. In DTN, the end-to-end connectivity between source nodes and destination nodes rarely exists. Due to this disruption connectivity, messages should be forwarded to intermediate participating nodes by using the \"store-carry-forward\" mechanism, if the source node intends to deliver messages to the destination node. Moreover, time is limited for intermediate participating nodes to transfer messages. That is why traditional routing protocols cannot work well in the \"store-carry-forward\" mechanism. Therefore, it raises a serious challenge in designing efficient routing protocols for DTN in many IoT applications. An efficient routing protocol in DTN has a direct contextual relevance to the data transmission in many IoT applications. In recent years, numerous protocols were proposed to maximize delivery success, such as First Contact [4], Epidemic [5], Spray and Wait [6], Probabilistic Routing Protocol using History of Encounters and Transitivity (PROPHET), [7] etc. Among them, PROPHET is a typical routing protocol based on historical data. However, there are some drawbacks in PROPHET [7]:  
* The delivered messages may be damaged by malicious intermediate nodes on the way from source to destination. * Messages are more likely to be aborted as there are too many intermediate nodes and hops on connected paths. * Due to TTL (Time to Live) and buffer congestion, some messages may be dropped on the way. In classic PROPHET, when two nodes encounter frequently, the delivery predictability will increase rapidly. However, if two nodes have no chance to encounter due to network failures in some time slots, the delivery predictability will decrease quickly. Furthermore, messages may be broken, dropped or aborted, due to the drawbacks of the management and transmission. In order to address the issues above and improve the PROPHET protocol, we propose a new routing protocol called Scheduling-PROPHET in this study, which can support more efficient routing performance in DTN for IoT applications. The main superiority of Scheduling-PROPHET is to improve the efficiency of transmission with low message lost and high delivery rate. The remainder of the study is organized as follows. Section 2 gives an overview of related work and presents the motivation for doing the research. In Section 3, we propose a new protocol in order to improve the PROPHET routing and illustrate our methods in detail. Section 4 presents the simulation results as well as the discussion.