OpenSnap: Collection of Globally Consistent Statistics in Software Defined Networks

Capturing and monitoring the global state of the network in a software defined network (SDN) is crucial for efficient routing, performance monitoring, Quality of Service (QoS) assurance, etc. The two major existing approaches for statistics collection in SDN are polling-based and event-based. Due to the asynchronous nature of the network, statistics collected through polling have inconsistencies and are not suitable for capturing the consistent global state of the network. On the other hand, event-based monitoring schemes may give sparse information about the network. Globally consistent state detection is well studied for asynchronous systems. However, current SDN standards such as OpenFlow do not support any functionality to collect globally consistent statistics. In this paper, we propose “OpenSnap”, an algorithm to determine the globally consistent state of the system. To support OpenSnap, we extend the OpenFlow protocol by adding a new action. The experimental results show that the statistics collected at the SDN controller using the proposed OpenSnap algorithm are always consistent.