TUS: A Transactional Update Service for SDN Applications

In this paper, we design a network update service for SDN applications to transactionally update the network. We name our system TUS, which is a layer sitting between the SDN controller and SDN applications. SDN applications can call TUS's interfaces to achieve atomicity, consistency, isolation, and durability guarantee for network updates, which eases the application's programming. TUS provides APIs for consistent update, uses logs for atomic update, applies optimistic concurrency control (OCC) for inter-update isolation, and checks each asynchronous rule update for durability. These design choices are decided by network unique characteristics and challenges - OCC can isolate network updates from volatile network states and checking asynchronous rule update is also used in implementing consistency guarantee in multi-phase network update. We prototype TUS, validate it consistency guarantee and failure recovery effectiveness, and also measure the overhead introduced by TUS logs.