# An Improved Opportunistic Routing Protocol Based on Context Information of Mobile Nodes
## 1 Introduction
The forwarding probability has similar characteristics with delivery predictability in PRoPHET protocol, i.e., increase for each contact, decay after contact, and transitivity. In [22], the authors propose a novel encounter based fuzzy logic routing, where the transfer opportunism of a node is computed while using fuzzy logic using the encounter and non-encounter duration, and messages are forwarded based on the transfer opportunism. In [23], the authors propose an encounter-based routing based on the observation that the future rate of node encounters can be roughly predicted by past encounters. In the encounter-based routing, the total copies of a message are limited and forwarding is decided based on the rates of encounters. In [24], the authors basically consider the spray and wait protocol, and propose a new metric called multi-probability, where a message can be forwarded to a node if any of its previously contact nodes has higher delivery predictability, even though the node does not have higher delivery predictability currently. Works on using mobility characteristics of mobile nodes for DTN have been carried out significantly [25; 26; 27; 28; 29]. In [25], mobility traces taken from UMass DieselNet, which consist of buses with WiFi interfaces that travel their routes, are used to forward messages, and the performance of the DieselNet routing is analyzed. They show the periodic behavior of inter-contact times aggregated at the router level. In [26], mobility traces from real public transport systems are characterized and used to improve the routing performance of DTN. Then, large scale mobility traces are produced using micro-mobility simulator and the performance of various DTN routing protocols are compared with the proposed algorithm. In [27], the authors propose a journey predictor for DTN based on mobility traces of public transportation system, where the journey predictor is based on a graph of predicted journeys and the best journey is selected to a specific destination. Artificial neural networks are used to predict a journey. In [28], a multi-copy routing scheme for a DTN based on an urban bus transportations system is presented and contact history of nodes is used to improve the routing of DTN. They propose a journey predictor based on artificial neural networks to select the best journey to a destination. In [29], nanosatellite communications link is used to cover a terrestrial sensor network that is based on DTN routing. The authors propose an optimal proactive fragmentation of DTN bundles, due to short contact duration between a nanosatellite and a sensor node, and show the performance enhancement over the reactive fragmentation approach. In related works, movement trajectory [10], movement direction, speed, estimated direction change, location [11; 12], movement pattern [13], contact period [14], last contact duration, last contact time, current contact time [15], contact count, contact duration, the amount of exchanged messages [16], contact history [17], node type [20], historical throughput, historical contact time [21], encounter duration, non-encounter duration [22], rate of encounters [23], and delivery predictability of previously contact nodes [24] are used to decide a message forwarding. Most of the mentioned context information, however, reflect individual characteristics of contact nodes or node itself, and collective characteristics of nodes have not been considered well to deliver a message to a destination node. In this paper, we propose an improved opportunistic routing protocol, where the context information of average distance travelled and average time elapsed from the reception of a message to the delivery of the message to the destination node is used. The context information such as average distance travelled and average time elapsed considered in this paper reflects the collective characteristics of a node to destination nodes, and we estimate that the collective characteristics are effective to decide a message forwarding in the DTN environment.