Devolve-Redeem
Rinku Shah, Mythili Vutukuru, Purushottam Kulkarni · 2017
Towards improving SDN control plane scalability, past work has proposed SDN controller frameworks that offload computation which depends on local state to controllers residing on the switches. Our work identifies another type of computation that can be offloaded to local controllers: that which depends on state that is generated globally but can be used within local controllers with loose synchronization. Because using such state locally incurs a synchronization cost, such offload makes sense only when the benefits of the offload out-weigh the synchronization cost. We present the design and implementation of Devolve-Redeem, an SDN controller framework that can offload computation to local controllers depending on the mix of various control messages in the incoming traffic. The offload decision in our framework is made by computing a cost metric that captures the relative costs of processing every control message at the central and local controllers, taking into account synchronization costs. The SDN application developer using our framework writes a single application that runs at both the central and local controllers, using our state management API to access offloadable state. Our framework migrates between various offload modes using the computed cost metric, by manipulating the rules in the SDN switches that forward control messages to the controllers. Our framework also transparently handles state synchronization between central and local controllers in a manner that is consistent with the offload mode. We have implemented the SDN-based LTE EPC application in our framework, and experiments with our prototype demonstrate the effectiveness of our adaptive offload framework.