A path computation element (PCE) is briefly defined as a control plane functional component (physical or logical) that is able to perform constrained path computation on a graph representing (a subset of) a network. A stateful PCE is a PCE that is able to consider the set of active connections, and its development is motivated by the fact that such knowledge enables the deployment of improved, more efficient algorithms. Additionally, a stateful PCE is said to be active if it is also able to affect (modify or suggest the modification of) the state of such connections. A stateful active PCE is thus able not only to use the knowledge of the active connections as available information during the computation, but also to reroute existing ones, resulting in a more efficient use of resources and the ability to dynamically arrange and reoptimize the network. An OpenFlow controller is a logically centralized entity that implements a control plane and configures the forwarding plane of the underlying network devices using the OpenFlow protocol. From a control plane perspective, an OpenFlow controller and the aforementioned stateful PCE have several functions in common, for example, in what concerns network topology or connection management. That said, both entities also complement each other, since a PCE is responsible mainly for path computation accessible via an open, standard, and flexible protocol, and the OpenFlow controller assumes the task of the actual data plane forwarding provisioning. In other words, the stateful PCE becomes active by virtue of relying on an OpenFlow controller for the establishment of connections. In this framework, the integration of both entities presents an opportunity allowing a return on investment, reduction of operational expenses, and reduction of time to market, resulting in an efficient approach to operate transport networks. In this paper, we detail the design, implementation, and experimental evaluation of a centralized control plane based on a stateful PCE, acting as an OpenFlow controller, targeting the control and management of optical networks. We detail the extensions to both the OpenFlow and the PCE communication protocol (PCEP), addressing the requirements of elastic optical networks as well as the system performance, obtained when deployed in a laboratory trial.
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