SDRS:集中与分布控制相结合的弹性多路径路由机制

SDRS:Elastic Multi-Path Routing Mechanism with Integration of Centralization Control and Distribution Control

传统的单播路由协议根据单一路由策略(如最小跳步数、最低代价等)计算出到达目的网络的最短路径.受限于局部视图的不完整性、局部策略的自私性,路由计算结果往往为非最优;同时,数据流传输完全依赖于单条路径,容易产生网络拥塞和由单点故障引起的通信中断.以软件定义网络(SDN)为代表的集中控制架构,通过感知网络状态,从全局视图进行路由计算并下发策略,促使网络路由趋近最优目标.文中提出了软件定义路由系统概念(Software Defined Routing System,SDRS),在分布式路由协议计算的分布路径基础上,将集中控制机理引入到路由控制系统,集中管理器通过最大多路径覆盖树算法计算出无环的集中路径集,并根据编排的策略选择性地把集中路径部署在网络中,从而实现分布与集中路径同时并行传输数据流,达到二者的有机耦合,既保留了原来分布式路由协议的柔性抗毁、快速自愈的能力,又吸收了集中控制的全局优化能力.最后,实现了SDRS原型系统.实验结果表明,在网络拥塞或单点故障时SDRS性能明显优于单播路由协议的性能,分布式路由协议的丢包率为20%时,SDRS系统的丢包率仅为2.94%.

Traditional unicast routing protocols deployed in the Internet just calculate shortest forwarding path for the same destination network by using single routing metric,such as least hops,lowest cost.Even unicast routing protocols can use equal cost multiple protocol(ECMP)to calculate several forwarding paths for one pair of end-to-end communication,they just work well under specific situations with proper network topology and proper metric.Due to incomplete information caused by partial-view of network status and selfishness of local strategy calculated by unicast routing protocols,the routing strategies usually are not optimal.Meanwhile,data-flow transmission completely relies on single forwarding path,leading to network congest and communication interrupt by a single failure(e.g.failure of link,failure of node,etc.).Software defined network(SDN),as the representative of centralized control mechanism,can obtain the global network status,perform routing calculation from global-view,and install routing strategies,hence to promote network toward optimal target.Unfortunately,centralized control architecture generally has bad system robustness and long delay of network status synchronization,thus it hardly has ability of flexible survivability and fast self-healing.Drawing further on this,this paper puts forwards Software Defined Routing System(SDRS),by introducing centralized control mechanism into existing routing system on basis of distributed paths generated by distributed routing protocol.SDRS establishes a closed-loop control system by integrating distributed routing protocol with centralized controller.On one hand,real-time link-status topology from distributed routing system is as the input for centralized controller.On the other hand,routing strategies of centralized paths calculated by centralized controller in return make influence on distributed routing protocol.Besides,centralized controller can calculate centralized path set without routing loops based on Maximum Multi-path Overlay Tree Algorithm,and selectively deploy centralized paths into network according to orchestration strategy.Thus,distributed path and centralized path can simultaneously transmit data-flow in parallel by coupling these two control mechanisms.These two aren’t in conflict with each other,because centralized paths generated by centralized controller include distributed paths.SDRS not only preserves the properties of flexible survivability and fast self-healing in distributed routing protocol,but also keeps global optimal ability of centralized controller.Finally,we implement SDRS prototype system,and our experimental results reveal that the SDRS can significantly promote the network performance especially in case of network congest or failure,e.g.,when distributed routing protocol has 20%packet-loss-ratio,SDRS just has 2.94%packet-loss-ratio.