Research On Unicast Routing In Delay Tolerant Networks

Delay tolerant networks (DTNs) characterize the networks that have the featuresof high transfer delay, high error rate and intermittent connection, etc.It was initiallyproposed for Inter Planetary Network (IPN) by United States Department of Defensein the last century. In2003, Kevin Fall formally proposed the structure of delaytolerant network at an international conference, and then attracted increasing interestof more and more researchers. The routing is a hotspot of research on DTN.In DTN model, the nodes are assumed to be mobile. So there is no end-to-endpath between a source and a destination. The communication of different nodesmainly relies on links that come up due to the mobility of nodes. That is the messagecan be sent to the node that its owner meets, and it will be got buffered and carried bythe second node until the next link comes up. That is the store-carry-forward methodapplied by most DTN networks. Using such kind method, researchers have proposedmany routing protocols.These protocols often send more than one copy of the same message to thenetwork. These copies are transmitted independently in order to enhance robustness.This brings the problem of redundant copy. That is when one copy of a messagereaches its destination, the other copies will still exist in the network, occupy bufferspace and may continue to be forwarded, wasting bandwidth, resulting in a decline innetwork performance.The message copies in delay-tolerant network leave the network mainly relyingon TTL and congestion control. The redundant copies are to be deleted due to them.But the two strategies are passive and may accidentally delete those copies ofmessages that haven’t reached destination. To eliminate the redundant copies moreeffectively, this paper proposes a redundancy elimination strategy based onacknowledge mechanism. In this strategy, we add an acknowledge field whichincludes the ID of the messages that have reached the destination in the packet header. The node received the messages will delete the redundant copies in its own bufferspace according to the acknowledge field. The intermediate node can update theacknowledge field when forwards the message to better redundancy elimination. Thereferences of update process are the arrival time and acknowledgement times ofmessage.In order to verify the proposed strategy, we use ONE to simulate it. We firstexpanded the platform, and then implemented the strategy on Epidemic and Spray andWait. Meanwhile, we did the simulations without acknowledge mechanism. Thesimulation results show that our strategy can effectively eliminate redundant copy andbe able to improve the network performance, such as delivery ratio and overheadratio.The main contributions of the paper are as follows:(1) on the basis of deepresearch and analysis of routing protocols of delay tolerant networks, we point out theredundant copy in multiple-copy routing protocols, and then propose a redundancyelimination strategy via acknowledge mechanism.(2) We use ONE to simulate theproposed strategy and verify its role of eliminating redundant copies and improvingnetwork performance.