Research Of The Routing Algorithms In Delay Tolerant Networks

With the rapid development of wireless communication technology, wireless network is applied more and more widely. The traditional network protocols often require a stable end-to-end path exists between the source node and the destination node. However, due to poor communication environment in deep space communications, aerospace and information network, disaster relief network environment, the link frequent interruption leading to end-to-end path does not necessarily exist, and the traditional routing protocols cannot work effectively. In this context, the concept of delay tolerant network (DTN, Delay Tolerant Network) came into being. Since DTN has a strong adaptability for the frequent interruptions, high error rate and large delay of link, it is very suitable for the restricted network. Currently, domestic and foreign researchers have made a lot researches about DTN, among these researches routing technology play a pivotal role and gradually become the focus of researches. Depending on the number of copies of the packets in the network, the existing routing algorithms are classified into Single-copy routing and Multiple-copy routing. Single-copy routing delivers message through multiple forwarding, having poor delivery rate and reliability, while the Multiple-copy routing copy and forward message through multiple paths, having higher delivery rate. Therefore, research on Multiple-copy routing has much more practical significance.Although the Multiple-copy routing has high delivery ratio and low transmission delay, but it has much larger network overhead since the plenty of packets producing in the network. Then, this article would optimize the existing multi-copy of the route from two aspects-the network coding and copy control, the main findings are as follows: (1) In DTN’s scenarios of Multi-type Data stream, traditional Network Coding Based Epidemic Routing(NCER) will increase the length of coding vector and the time of waiting for decoding in destination code, since it cannot encodes packet of different type separately. In view of NCER’s disadvantage, this article proposes an improved Network Coding based routing-BNCER (Business based Network Coding in Epidemic Routing) routing algorithm based on NCER routing. The BNCER could reduce the encoding vector length of the encoded information and the recovery time of each business stream decoding effectively by coding different business streams separately, and make the business flow could be transported independently, to improve the efficiency of data transmission. The simulation results show that compared with NCER, BNCER plays better performance in the average transmission delay and packet delivery ratio, transmission delay decreased by about40%, packet delivery rate increased by about12%.(2) In view of that the distribution of copies is blind in the original Spray and Wait routing, this article proposes a routing algorithm based the node Delivery Utility dissemination wait DU-SW (Delivery Utility Based Spray and Wait). DU-SW algorithm takes full advantage of the historical encounter information between nodes to count the frequency of node encounter, and to define the node Delivery Utility index. The proportion of the quota allocation of a copy of message is determined by the delivery effectiveness ratio between nodes. On the basis of this algorithm, the node with a higher algorithm gets more quota. In DU-SW algorithm, without increasing the network overhead, the delivery probability is improved through distributing the limited copies quota rationally. In the simulations, DU-SW algorithm is better than the SW algorithm in packet delivery ratio, average transmission delay and network overhead rates, packet delivery rate increase of about8%, and average transmission delay is reduced by about15%, reduced network overhead about20%.