软件定义网络中延迟满足的路由选择与实时调度更新

由于数据流的动态性和流量负载转移，软件定义网络（software defined networking，简称SDN）需要频繁更新数据平面以优化网络性能.大多数已有路由更新策略首先根据网络当前流量状态确定目标路由配置，然后更新数据流的路由.然而，由于交换机基于TCAM（ternary content addressable memory）进行流表更新的速度较慢，导致路由更新的延迟通常较大.当网络规模大或网络拓扑结构经常变化时，路由更新的延迟可能更大.研究发现，大多数数据流的持续时间很短且整个网络的流量强度在一段时间后会发生变化.如果路由更新延迟过长，更新后的路由配置可能不再有效.为此，研究了SDN的实时路由更新问题，提出了延迟满足的路由选择和调度更新策略（delay satisfied route selection and updating scheme，简称DSRSU）.与大多数现有研究不同，DSRSU同时从控制平面路径选择和数据平面的更新调度两方面来联合优化，降低路由更新的延迟.路径选择阶段只选择部分数据流进行路由更新；更新调度阶段通过建立更新关系图挖掘数据流的更新先后顺序，进一步加快路由更新速度.仿真分析结果表明，与现有几种路由更新策略相比，DSRSU能够在大幅度降低路由更新延迟的同时，达到与现有策略相似的网络性能.

Delay Satisfied Route Selection and Real-time Update Scheduling in Software Defined Networking

Software defined networking may need to frequently update their data planes to optimize network performance due to flow dynamics or traffic load transfer. Most existing strategies first determine a target route configuration based on the current network flow status. Then, flows in the network are updated to the target route configuration. However, since the low operation speed of ternary content addressable memory (TCAM) for flow tables update, route updates usually gets long delay. Moreover, route updates delay will get longer in a large or topology frequently changed network. According to recent works, most flows have short durations and the total flows intensity may vary after a certain time period. Hence, the new route configuration may be inefficient if the route update delay takes too long. In this study, the real time route update for SDN is addressed and a delay satisfied route selection and updating scheme (DSRSU) is proposed. Different from most existing studies, DSRSU jointly considers the flow route selection in the control plane and route update scheduling in the date plane to reduce the route update delay. More specially, only a subset of flows is chosen for route updates in route selection. To further improve the update speed, an update dependency graph is established to explore the scheduling order of the flows during update scheduling. Simulation results demonstrate DSRSU can largely reduce the route update delay compared with previous route update strategies while maintaining a similar route performance.