Coriant adds optical control to SDN framework

Coriant's CTO, Uwe Fischer, explains its Intelligent Optical Control and how the system will complement Transport SDN.

"You either master all that complexity at once, or you find the right entry point and provide value for each concrete challenge, and extend step-by-step from there" 

Uwe Fischer, CTO of Coriant

Coriant has deployed a networking framework that it says will comply with Transport SDN, the software-defined networking (SDN) implementation for the wide area network (WAN).

The company's Intelligent Optical Control system is already deployed with one large North American operator while Coriant is working to install the system with other Tier 1 customers.  

Work to extend SDN technology beyond the data centre to work across operators' transport networks has just begun. The Open Networking Foundation (ONF), for example, has established an Optical Transport Working Group to define the extensions needed to enable SDN control of the transport layer and not just packet.

"SDN and optical networking go together nicely; they are not decoupled but make up an end-to-end overall framework," says Uwe Fischer, CTO at Coriant.

The Intelligent Optical Control is designed to tackle immediate networking issues as Transport SDN is developed. Coriant says its system complies with the ONF's three networking layer SDN model. The top, application layer interfaces with the middle, control layer. And it is at the control layer where the SDN controller oversees the network elements found in the third, infrastructure layer. 

Intelligent Optical Control adds two other components to the model. An extra intelligence component in the control layer that sits between the SDN controller and the infrastructure layer. This intelligence is designed to exploit the intricacies of the optical layer.

Coriant has also added an application at the topmost layer to automate operational procedures. "SDN at the application layer is centered around service creation," says Fischer. "We see a complete set of other applications which automate operational workflows."

Optical intelligence

One key benefit of SDN is the central view it has of the network and its resources. Such centralised control works well in the data centre and packet networking. Operators' networks are more complex, however, housing multiple vendors' equipment and multiple networking layers and protocols.

The ONF's Optical Transport Working Group is investigating two approaches - direct and abstract models - to enable the OpenFlow standard to extend its control across all the transport layers.

With the direct model, an SDN controller will talk to each network element, controlling its forwarding behaviour and port characteristics. The abstract model, in contrast, will enable the controller to talk to a network element or an intermediate controller or 'mediation'. This mediation performs a translator role, enacting requests from the SDN controller.

The direct model interests certain ONF members due to its potential of reduce the cost of networking equipment by moving much of the software from each element to the SDN controller. The abstract model, in contrast, has the benefit of limiting how much the controller needs to be exposed to the underlying network's details.    

Coriant says it has yet to form a view as to the benefits of the direct and abstract ONF models. That said, Fischer does not see any mechanisms being discussed in the ONF that will fully exploit the potential of the photonic network. Accordingly, Coriant has added its own intelligence that sits between the SDN controller and the photonic layer.

“We fully comply with the approach of an SDN controller, however, we put another layer in between the control layer and the infrastructure layer,” says Fischer. “We consider it a part of the control layer, but adding the planning and routing intelligence to leverage the full performance of the infrastructure layer underneath."

Fischer says there is a role for abstraction at the photonic layer but perhaps only for metro networks. "We currently don't think this will really extend to the wide area photonic layer," he says.

"The added intelligence can leverage the full performance of the WDM network because it knows all the planning rules in detail," says Fischer. It does multi-layer optimisation across the transport layers. Coriant has added the intelligence because it does not think the transport-network-specific aspects can be centralised in a generic way.

Automated operations

Coriant's Intelligent Optical Controller also adds an application to automate operational procedures. Fischer cites how the application layer component benefits the workflow when a service is activated in the network.

With each service request, the Intelligent Optical Control details whether the new service can be squeezed onto existing infrastructure and details the service performance parameters to be expected, such as latency and the guaranteed bandwidth. "The operator can immediately judge the service level they would get," says Fischer.

Another planning mode supports the adding of equipment at the infrastructure layer. This enables a comparison to be made as to how the service level would improve with extra equipment in place.

If the operator can justify that business case for new hardware, the workflow is then automated. The tool creates the bill of materials, the electronic order, and the configuration and planning data needed to implement the hardware in the network.

Coriant says equipment and services can be time-tagged. If an engineer is known to be visiting a site once the hardware becomes available, the card can be pre-assigned and automatically used once it is plugged in. "There is a full consistency as to how the hardware is managed and optimised towards service creation," says Fischer.

Coriant is working with its major customers to create a testbed to demonstrate an SDN implementation of IP-over-DWDM. "It will involve interworking with third-party routers, and using SDN controllers to control the packet part of the network with Openflow and other mechanisms, and then connected to the Intelligent Optical Controller."

The goal is to demonstrate that Coriant's approach complies with this use case while better exploiting the optical network's capabilities.

Fischer says optical networking is moving to a new phase as transmission speeds move beyond 100 Gigabit.

"We are entering an interesting phase as capacity and reach hit the limits of practical networks," he says. "This means we are talking about flexible modulation formats and variously composed super-channels for 400 Gigabit and 1 Terabit."

In effect, a virtualisation of bandwidth is taking place at the photonic layer. "This fits nicely into the SDN principle as on the one hand it virtualises capacity, which very much fits in the model of virtualising infrastructure." 

But it also brings challenges.

"There is currently not a good practical means to manage such flexible capacity at the photonic layer," says Fischer. This, says Coriant, it what its customers are saying.  It also explains Coriant's decision to add the optical controller. "You either master all that complexity at once, or you find the right entry point and provide value for each concrete challenge, and extend step-by-step from there," says Fischer.