—This paper presents the CONTRACT framework to address a fundamental deficiency of the IP network control plane, namely the lack of coordination between an IGP and other control functions involved in achieving a high level objective. For example, an IGP’s default automatic reaction to a network failure may result in an SLA violation, even if the IGP link weights have been carefully chosen. This is because an IGP blindly routes traffic along the shortest paths based on link weights, and it is completely oblivious to the interactions between SLA compliance, load balancing and traffic policing objectives in a network. The CONTRACT framework makes it possible to coordinate these objectives. Under this framework, routers continue to operate autonomously, but they also coordinate their actions with a centralized network controller, which evaluates the impact of routing changes, decides whether the changes are SLA compliant, and performs load rebalancing and/or packet filter reconfig...
Zheng Cai, Florin Dinu, Jie Zheng, Alan L. Cox, T.