Abstract: In order to forward multimedia messages completely and quickly in a limited time, nodes divide messages into several fragments and send fragments separately in opportunistic networks. The influence of fragments size on the performance of multimedia messages forwarding is mainly studied, then a method of determining the reasonable scope of the fragments size and an experience value are put forward. DeLay and message deliver ratio are analyzed under the random walk model of four classic routing in ONE environment. The results show that with the increase of the fragment size, the delay of destination node received the complete message presents a trend of first decline and then increases; and within a limited time, message delivery ratio tends to increase first and then decline.

Key words: opportunistic networks, multimedia messages, fragments, expected communication time, expected number of communications

摘要： 在机会网络中，为了在限定时间内快速且成功地转发多媒体消息，通常将消息划分成数据块进行转发。重点研究了数据块大小对多媒体消息转发性能的影响规律，提出一种确定分块大小合理范围的方法并给出了一个经验值。在ONE仿真环境下，对随机游走模型下四种经典路由的延迟和递交率进行了统计分析以验证此思想。实验结果表明随着分块大小增大，目的节点接收到完整的多媒体消息耗费的延迟呈先下降后上升的规律；在限定的时间内，消息的递交率呈先上升后下降的规律。

关键词: 机会网络, 多媒体消息, 数据分块, 期望通信时间, 期望通信次数