中文摘要：

为了应对DTN网络的动态连通特性,现有路由策略常常利用“携带-转发”消息传输技术,通过推测未来相遇机会选择消息中继路径.但这种机会数据传输方式的效果具有偶然性.对中继选择策略的性能进行实证性研究,以获得关于中继效率不确定性特征的基本认识.首先,介绍一种基于剩余延迟比较的机会中继选择策略,该策略以移动节点对之间的历史联系记录和最近相遇以来的经历时间为基础,估计消息的直接转发剩余延迟,通过比较剩余延迟选择合适的中继节点;由于仅使用本地信息,该策略的运算和通信开销小,并且易于实现;其次,在基于大规模实际车辆移动轨迹的车载DTN环境中,对机会传输的中继效率进行经验性研究.主要关注的问题是：基于推测所选择的中继能够使得端到端传输延迟降低的概率是多少？恰当选择的中继节点可以降低的延迟比例是多少？这种实证性的研究对于未来机会车载网络中的协议设计和应用推广有着重要的实际价值.

英文摘要：

To accommodate the dynamic connectivity and networking condition in DTN, most existing routing schemes require inferring future contact opportunities to select message relays. However, such relay only has an incidental effect on helping opportunistic data delivery. In order to again a further understanding of the intrinsic uncertainty of relay efficiency, this paper engages in an empirical investigation on the relay selection schemes. Firstly, it introduces a more effective opportunistic relay selection strategy based on the estimation of residual message delay, which utilizes pairwise contact records and the elapsed time from last contact. Next, based on the underlying opportunistic vehicular network extracted from large-scale realistic vehicle traces collected from urban areas, it investigates the efficiency of relay selection with an empirical view. The questions this study focuses on are： What is the probability that a selected relay can make the end-to-and delay reduced？ How much the latency can be saved by a properly selected relay？ Such empirical study is signficant for the protocol design and application deployments in the future opportunities vehicular networks.