Walk the line: consistent network updates with bandwidth guarantees

New advances in technologies for high-speed and seamless migration of VMs turns VM migration into a promising and efficient means for load balancing, configuration, power saving, attaining a better resource utilization by reallocating VMs, cost management, etc. in data centers. Despite these numerous benefits, VM migration is still a challenging task for providers, since moving VMs requires update of network state, which consequently could lead to inconsistencies, outages, creation of loops and violations of service level (SLA) agreement requirements. Many applications today like financial services, social networking, recommendation systems, and web search cannot tolerate such problems or degradation of service [5, 12]. On the positive side, the emerging trend of Software Defined Networking (SDN) provides a powerful tool for tackling these challenging problems. In SDN, management applications are run by a logically-centralized controller that directly controls the packet handling functionality of the underlying switches. For example, OpenFlow, a recently proposed mechanism for SDN, provides an API that allows the controller to install rules in switches, process data packets, learn the topology changes, and query traffic counters [13]. The ability to run algorithms in a logically centralized location, and precisely manipulate the forwarding layer of switches creates a new opportunity for transitioning the network between two states. In particular this paper studies the question: given a start-