I. Introduction
Delay Tolerant Networks (DTN) [8] are an emerging class of networks wherein the underlying network between the communicating devices is not fully connected. Consequently, it is very rare that an explicit end-to-end path is available between the source and destination. Rather the topology is made up of intermittently and partially connected node clusters. DTN rely on the inherent mobility of the participating nodes to store-carry-and forward [4] the messages for delivery to the destination. DTN are particularly attractive for use in areas where there is no communication infrastructure due to harsh environments (battlefields, forests, space) or economic conditions (rural and remote areas, developing countries). Of course, such networks are suitable for running applications, which can tolerate large delays such as transferring files and non-interactive messaging. Two particularly attractive instances of DTN include (i) Pocket Switched Networks [10], wherein personal communication devices carried by humans self-organise to form an intermittently connected network, enabling a new class of social networking applications (e.g.: PeopleNet [16]) and (ii) Vehicular DTN, which can leverage the large data storage and energy capabilities offered by vehicles to create a large-scale powerful DTN. Examples include the use of vehicle-based DTN to provide low cost digital communication to remote villages [17] and vehicular sensing platforms such as CarTel [7] for urban monitoring.