ENP Newswire -
Release date- 06062014 -
A cluster-based distributed controller runs on multiple physical controllers as a single logical controller to control multiple network switches. Compared to conventional centralized controllers, cluster-based distributed controllers offer better scalability and improved failure tolerance. Until now, however, the problem was that they had difficulty handling sudden load fluctuations and coordinated control when there was a controller failure.
By deploying an SDN with these technologies to a wide-area network, infrastructure can recover quickly from disasters or other network failures while maintaining steady network operations.
These technologies are being presented at
Existing SDNs such as OpenFlow are designed for centralized control, which means that operating wide-area networks, configured with switches transferring large volumes of communication packets, as SDNs results in highly concentrated loads in the controller when the number of users increases. This will be an obstacle to the smooth provision of service, and if the controller itself fails, the switch that it had been managing can no longer be controlled.
This technology consists of a module for control applications that is an add-on to existing controller applications, and a distributed controller module that connects multiple distributed controllers as components of an OpenFlow controller so that, depending on loads, application and controller components can be added along with server resources.
Cluster-based distributed controllers are different from centralized controllers in that multiple distributed controller modules need to be run in a coordinated way so that they do not compete with each other. Another challenge is ensuring continuity of control. Processes need to keep running even if a module fails, but difficulties are encountered with automatic switchovers when some controller components are heavily loaded or fail, and processing by the switches managing the controllers slows down or control becomes unsustainable.
About the Technology
If load rebalancing is judged to be needed according to the load-balancing logic, which switches to be reassigned are decided based on switch-reassignment logic, to balance the load according to a policy for CPU utilization rates and number of switches. As a result, the correspondence between the changed switches and the controllers is registered in the coordination system and the load is balanced by reassigning the switches in accordance with the updated information from the distributed-controller.
Uninterrupted Recovery Technology
This changes the controller/switch correspondence information to redistribute loads automatically based on controller-component load information (CPU utilization rates and number of switches) (step 4).
The distributed-controller coordination modules that have not failed link to the information update and activate it to reassign the controllers managing switches so that operations continue without any interruption in service. Because the controllers that are the reassignment destinations are decided using load-balancing technology, no controller should experience a sudden load spike that would cause it to shut down.
Furthermore, even if the leader module itself suffers from a failure, the coordination system will detect a session interruption and select a new leader, and that leader module will determine controllers to manage switches again.
Using the cluster-based distributed controller makes it possible to handle sudden load fluctuations and to maintain continuity of network services even when controllers fail, enabling stable, highly reliable operations of wide-area networks.
For example, in the case of conventional controllers, when they are duplicated in the hot standby mode, i.e. active and on standby, for a ten-domain network, the total required number of the controllers is 20, or specifically two per domain. By contrast, using cluster-based distributed controllers, just one standby controller is added to the regularly running ten controllers, so that only 11 controllers are needed, enabling a reduction in the number of controllers by nearly half.
This technology could be used in the networks of telecommunications carriers and other network infrastructure to achieve highly reliable, stable operations with lower deployment costs and lower operating costs.
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