Taming SDN Controllers in Heterogeneous Hardware Environments

The ability to deploy applications which control network resources using a global view is a major benefit of the SDN paradigm. The SDN dataplane is comprised of a topology of forwarding elements programmed by a centralized controller over a common, well-defined interface. We believe that the heterogeneity of forwarding devices is an inherent property of software defined networks rather than a side effect. Therefore it is vital to design SDN frameworks in manner which explicitly takes variable hardware capabilities into account. In this work we argue that the concurrent operation of switches with diverse capacities for control message processing leads to unpredictable delays in SDN applications. To address this issue, we use a queuing model to characterize the service of a switch's control interface. Furthermore, we outline a measurement based-approach to derive the corresponding parameters. We propose a simple interface extension for controller frameworks which enables operators to configure delay bounds for transmitted control messages. As a result, developers can create SDN applications which exhibit consistent and predicable behavior.