# Energy Efficient Policies for Data Transmission in Disruption Tolerant Heterogeneous IoT Networks
## 2 Related Work  
Although it has been clear for many years that a major challenge for the IoT is its ability to cope with the high network dynamism, it is only recently that DTNs have been identified as potential enablers for the IoT. For example in [10] the authors develop a Bundle Protocol (BP) convergence layer for IEEE 802.15.4-based networks and evaluate it through a use case that involves an elevator carrying a sensor. Another example is [11] where a basic implementation of a BP binding for Constrained Application Protocol (CoAP) is proposed, as a means to enable delay tolerant IoT, and some first experimentation results are presented that validate the feasibility of the approach.  
There are numerous other works where IoT, Wireless Sensor Networks and DTNs coexist. In [12] the authors present opportunistic IoT, which addresses information dissemination and sharing within and among opportunistic communities which are formed by the movement and opportunistic contact among humans bearing smart devices. In [13] the authors discuss the notion of a Challenged IoT and propose Direct Interaction with Smart Challenged Objects, a technique that enables objects to convey their interface directly to other mobile users. In [14] the authors present a novel buffer management algorithm for DTNs, called SmartGap, that estimates the value of each packet by means of its contribution to the reconstruction of the original signal to be transmitted. More recently, in [15] the authors present a collection of survey papers related to DTN routing as well as most of the aforementioned works that utilize DTNs in order to tackle IoT related problems.  
A work that is more closely related to ours, in terms of the network architecture considered, is [7] where the authors consider a DTN with intermittent connection between mobile nodes that are equipped with two radio interfaces. The first one is a long-distance radio which is used for neighbor discovery while the second one is a 802.11 interface used for data transmission. Furthermore, the authors consider using battery powered stationary nodes, called \"Throwboxes\" in order to increase the number and frequency of contact opportunities for the mobile nodes. The authors tackle the problem of reducing the energy consumed in neighbor discovery and, more specifically, their objective is to maximize the number of packets being forwarded by Throwboxes under an average power constraint by utilizing mobility prediction. Similar to [7] the authors in [16] consider solar powered mobile nodes in a DTN that again have two wireless interfaces. The first one is a 802.15.4 interface which is used by a power management module that is responsible for negotiating complex wakeup rules whenever a potential contact with another mobile node is feasible, while the second one is a 802.11a used for data transmission. The focus of this study is again to minimize energy consumption related to the discovery of communication opportunities. Unlike the previous two works we utilize both the long and short range interface for data transmission while we do not consider the problem of neighbor discovery.  
Finally, in [17] the authors provide a comprehensive survey of DTN related works that consider the use of throwboxes as performance enhancers. The works surveyed [17] consider a wide range of problems related to the use of throwboxes such as their cardinality, placement criteria, buffer management, network topology, mobility characteristics of nodes, application requirements, and cooperation of throwboxes among themselves and with other nodes. However, none of these works works addresses the same problem or considers a system model that is similar to the one we consider.  
To our knowledge our work is the first one to address the problem of finding an energy efficient packet transmission policy for a mobile node that participates in a DTN IoT network where mobile nodes are equipped with two wireless interfaces for data transmission.