中文摘要：

虚拟网络广泛采用隧道技术来实现链路虚拟化。为快速检测虚链路的状态，设计和实现了一种轻量级的检测协议。该协议综合利用了主动和被动两种检测机制：主动检测机制周期性地发送控制报文对链路状态进行探测，被动检测机制通过监控数据流量来确定链路状态。在VegaNet虚拟网络实验平台进行了实验，实验结果表明：该协议的检测延迟约为90～130ms，故障持续时间的检测误差趋于0；当虚链路存在数据流量时，该协议没有引入任何探测报文开销。该虚链路状态检测协议可以适用于任何形式的隧道虚链路，对于构建真实感和可控的虚拟网络具有重要的应用价值。

英文摘要：

IP tunnels are widely used for link virtualization in virtual networks. This paper presents a lightweight link detection protocol called the virtual link state detection protocol （VLSDP） to detect the state of the links in virtual networks. VLSDP leverages both active and passive detection mechanisms. Active detection periodically sends probing packets between the ends of a virtual link, while passive detection monitors data traffic in the virtual link to infer link states. VLSDP was deployed in the VegaNet testbed to show that the detection delay is between 90 and 130 ms and the failure duration deviation is about 0. Moreover, the results show that VLSDP does not generate any probing traffic in the presence of data traffic over virtual links. The VLSDP is applicable to different types of tunnel based virtual links, and the concepts can be used in realistic and controllable virtual networks.