Flex-grid prevents network traffic jams

A flexible-grid system that controls connections in optical networks can also redirect traffic to other networks, avoiding gridlock.

Similar to how services like Google Maps use algorithms to determine the fastest route from point A to point B, researchers from Spain and Japan have achieved this kind of traffic control for the connections in optical networks using a new dynamic network management system – and it goes one step beyond Google Maps. If necessary, the flexible-grid system can also redirect traffic by re-arranging one or more existing connections, preventing network traffic jams from occurring when a new single connection is made.

This system design, from Catalonia Technological Center of Telecommunications (CTTC) and KDDI R&D Labs in Japan, combines two elements: an OpenFlow controller and a so-called “stateful” path computation element (PCE).

The Catalonia Technological Center of Telecommunications (CTTC) Adrenaline test bed shows an MPLS-TP access and aggregation network over a four-node wavelength-switched optical transport network. The multilayer network can be controlled by either a distributed GMPLS control plane or an integrated stateful path computation element (PCE)/OpenFlow centralized control plane. MPLS-TP = multiprotocol label switching-transport profile; GMPLS = generalized multiprotocol label switching. Courtesy of CTTC Optical Networking Area, Spain.

An OpenFlow controller uses a protocol that allows the behavior of a network device – regardless of its manufacturer – to be remotely configured and, “by extension, provides a way to operate a network using a logically centralized element that can see the network as a whole,” said CTTC research associate Ramon Casellas. This enables packets of data to navigate the path of switches on a network much more efficiently than with traditional routing protocols, as if there were multiple, but coordinated, remote traffic controllers helping to guide the network.

A PCE is a dedicated computer that finds network routes between end points, similar to Google Maps or GPS navigation systems, Casellas said. A stateful PCE, however, is smarter because it keeps track of and considers current connections to improve and dynamically correct the path computations for all of the connections in the network, he said. Because the existing connections are stored in an internal database, advanced algorithms can use information about them to enhance network speed and efficiency. They do this by improving the optimization of the active connections as a whole instead of individually.

“The underlying idea,” Casellas said, “is that having extra information is helpful to improve the performance of the path computation, and thus the network. An active, stateful PCE also can affect the status of the active connections. For example, an active, stateful PCE is able to rearrange active connections to allocate new ones.”

Essentially, the system knows every connection on a network and what it is doing at any given time, with the ability to re-route those connections midstream based on new connections coming into the network.

The investigators tested the system by using it to dynamically control the optical spectrum in the fibers in a flexi-grid optical network. In these networks, the intrinsic constraints of the optical technology justify PCE deployment, Casellas said.

“Combining a stateful PCE with OpenFlow provides an efficient solution for operating transport networks,” he said. “An OpenFlow controller and a stateful PCE have several functions in common but also complement each other, and it makes sense to integrate them. This allows a return on investment and reduces operational expenses and time to market.”

The research, titled “An Integrated Stateful PCE/OpenFlow controller for the Control and Management of Flexi-Grid Optical Networks,” was presented at OFC/NFOEC 2013 in Anaheim, Calif.