基于流量特征的OpenFlow南向接口开销优化技术

Reducing the Southbound Interface Overhead for OpenFlow Based on the Flow Volume Characteristics

软件定义网络(software defined networking,SDN)分离的数据平面和控制平面,给网络管理带来了开放性和灵活性.但同时控制器与交换机之间的接口(控制器南向接口)需要更频繁的交互各种消息以实现对网络的控制.一方面,数据平面触发Table-Miss的数据包需要通过Packet-In消息往返于交换机与控制器之间,时延增大的同时也给控制器南向接口带来繁重的通信开销,数据平面和控制平面之间的交互容易成为网络性能的瓶颈.另一方面,控制器在下发新的流表项时,由于缺乏新表项对应的数据流特征信息,易出现已有的大流表项被下发的小流表项替换的情况,造成冗余的Flow-Mod消息(流表更新消息)和Packet-In消息,进一步加重了南向接口的通信开销,降低了网络的整体性能.提出一种基于流量特征的OpenFlow南向接口开销优化技术uFlow,在控制器上通过对Packet-In消息中数据流量特征的识别以及对小流的直接转发,达到消除南向接口冗余开销的目的.对uFlow的原型系统进行了实现,并通过真实网络中的流量对uFlow优化效果进行了验证.实验结果显示:与传统的OpenFlow网络处理方式相比,uFlow消除了冗余的交换机流表项更新,显著地降低了OpenFlow南向接口的交互开销:在不同的网络负载和流表容量的情况下,uFlow平均能减少70%以上的Flow-Mod消息.

Software defined networking(SDN)decouples the control plane from the switch in the data plane,which forms the SDN controller.This paradigm introduces many benefits,e.g.,openness,management simplicity,etc.Nevertheless,the separation of the SDN switch and the controller also leads to great communication overhead between them due to controlling the network(the number of the control message and Table-Miss packets),and the overhead becomes the major bottleneck of SDN.On the one hand,each Table-Miss event can produce multiple Flow-Mod messages which add extra bandwidth overhead as well as delay to the southbound interface.On the other hand,controller has no awareness of flow characteristic information behind the Flow-Mod messages which make the overhead worse.This paper proposes a new architecture uFlow(split up Flow)to mitigate the overhead at the controller side based on the flow volume characteristics.We implemented the prototype of uFlow system both in software-based platform mininet and hardware-based platform ONetSwitch.Experimental results driven by the real traffic show that uFlow can significantly reduce the communication overhead between control plane and data plane,the number of the control message has a decrease of 70%off on average,eliminate redundant update of flow entries in switch and reduce the transmission delay of packets.