Sometimes end to end connectivity may not exist between the nodes, sometimes it is too expensive to connect all the networks and sometimes due to some catastrophic effect, exchanging of messaging are difficult, so it can cause delays from hours to days, hence networking of this type of situation is called as Delay Tolerant Network. As no end to end connectivity between the nodes so it require buffer at each node to store incoming messages. The network uses a store-carry-forward mechanism, while sending a message from one node to another node. Messages which are stored at each node carry along with him until it reaches to the next node and then forward. Here two scheduling policies are named as PRIORITY+ algorithm and FACTOR algorithm. PRIORITY+ algorithm considers a priority of message with different routing algorithm. FACTOR algorithm considers the TTL value with priority of that particular message. Algorithms can achieve better delivery ratios with less overhead and latency ratio.

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A vehicular delay tolerant network (VDTN) is a special type of delay tolerant network (DTN), where messages are carried by vehicles from one end to another end. End-to-end connectivity in a VDTN is episodic because an end-to-end path between different source nodes and destination nodes does not exist and therefore the possibility of delivering messages to the destination node reduces drastically. Underlying routing protocols of Mobile Ad-hoc Network (MANET) fail when applied to a VDTN because of the non-existence of an end-to-end path that is used to carry packets to the destination. Thus, routing becomes the challenging task in a VDTN. Different types of routing algorithms are proposed for a DTN in the literature but very few algorithms have been proposed that take into account the past history of nodes. In this paper, we propose a contact history based routing algorithm explicitly designed for a VDTN that exploits the history of a node to find the best candidate relay to take a decision to forward a message to the destination. This contact history contains every node's past encounters with relay nodes that had come in contact with this node in the past. We show that, our algorithm outperforms existing history based approaches as well as few non-history based approaches in terms of message delivery ratio, overhead ratio and average delivery latency.