Study On Routing Technologies In Delay And Disrupution-Tolerant Mobile Ad Hoc Networks

Delay and Disruption Tolerant Mobile Ad Hoc Network (DTN) is a new approach to wireless networks that may lack continuous network connectivity. The key distinguishing feature of a DTN from a Mobile Ad Hoc Network (MANET) is that there may never be a complete end-to-end path, or such a path is highly unstable and may change or break soon after it has been discovered. Since no end-to-end routing pathes exists most of the time in DTN, conventional MANET routing protocols (synchronous routing) would fail in this context. Therefore, it is necessary to study and improve the performance of asynchronous routing protocols that forward messages by the store-carry-and-forward pattern.As an original asynchronous routing protocol, the Epidemic routing protocol can effectively guarantee the delivery ratio at the cost of high overhead in terms of message replications. This would results in poor performance of Epidemic routing especially in buffer size constraint networks. In this dissertation, we proposed a new routing protocol, called Adaptive Randomized Epidemic Routing (ARER). ARER dynamically adjusts the forwarding probability for each message according to the replication density. The theoretical analysis and simulation results show that our proposed protocol can effectively improve the performance of Epidemic routing.To reduce the overhead of routing protocols in DTN, we introduced the Directional Forward scheme into asynchronous routing and proposed Asynchronous Directional Forward Routing (ADFR) protocol. Using ADFR, a node caches the position information that it ever meets, and selects the appropriate relays according to the directional angles formed by the Neighbor Vector and Destination Vector. Furthermore, ADFR limits the numbers of forwarding messages in one contact by estimating the contact duration. The simulation results show that ADFR outperforms Epidemic, Spray-and-Wai and ARER in all scenarios in terms of delivery ratio and delivery delay.Most of asynchronous routing protocols ignore the existence of partial multi-hop paths in DNT. Thus, they adopt hop-by-hop forwarding pattern and usually miss some appropriate delivery opportunities. Based on the study of ADFR, we proposed a new hybrid routing protocol, called Hybrid Directional Forward Routing (HDFR). HDFR combines the positive aspects of DSR and ADFR. The simulation results show that HDFR can improve the message delivery ratio by discovering and utilizing the partial multi-hop paths in networks.Since the performance of asynchronous routing protocols is affected by contact duration and buffer size of nodes, the priority of message forwarding and dropping should be arranged. In this dissertation, we proposed a Weighted Schedule Mechanism (WSM) based on the Multiple Attribute Decision Making theory. With this new method, the delivery ratio of asynchronous routing protocols can be improved.