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Plexxi SDN includes tiered controller, data center-based WDM

Startup Plexxi's software-defined networking products include a tiered SDN controller and dynamic bandwidth allocation based on WDM.

Startup Plexxi introduced a software-defined networking technology that applies wavelength-division multiplexing within a data center to enable applications to demand the network resources they need, all the way down the physical layer of the network.

The use of wavelength-division multiplexing (WDM) between switches allows Plexxi's software-defined networking (SDN) architecture to dynamically allocate bandwidth between its top-of-rack switches using different spectrums of light. The Plexxi SDN architecture splits the control plane between the individual switches and a central controller, and it includes a sophisticated northbound interface that presents a network abstraction for orchestration systems and applications.

"The whole beauty of WDM is that you've got one piece of glass [in the fiber optic cable], but you're running simultaneous data conversations across it at different wavelengths of light," said Eric Hanselman, research director for networks at London-based 451 Research. "As long as you select the wavelengths carefully, they don't interfere and … you've now got all sorts of capacity."

The Plexxi SDN solution: Affinity Networking

The Plexxi SDN solution, Affinity Networking, starts with Plexxi Control, a tiered SDN controller. The central controller performs tasks that don't require real-time computation in the data path, such as planning and optimization. Each Plexxi switch has its own control element that performs distributed processing for real-time forwarding. The distributed control element also offers scalability and resiliency.

"We chose to do [a tiered controller] because in the conventional OpenFlow architecture, the controller is occasionally in the data path," said Dave Husak, founder and CEO of Cambridge, Mass.-based Plexxi. "Every time a new flow starts up, shuts down or changes, the controller has to push those packets around until it can configure the switches for it. It's a big scaling problem. Your controller is going to rate limit how fast things can attach to the network and how fast the flows can change, because the controller is in the data path."

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Plexxi Control does not use OpenFlow to control the network. "The interface between our controller and switch is our own," said Mat Mathews, co-founder and vice president of product management for Plexxi. "It looks like OpenFlow, but what OpenFlow is doing is at a very device-centric level. What comes out [of] our controller is actually a set of network directives, not flow table entries -- things like, 'Here's what the network needs to look like to satisfy the application. That's nothing that OpenFlow can satisfy. The controller that sits on our individual switches is more device-centric. It's going to take those network directives from the central controller and translate it into device-centric information like flow table entries, or in our case, the ability to reprogram the physical interconnect."

The physical layer of the product is Plexxi Switch 1, a top-of-rack switch with 32x10 Gigabit Ethernet (GbE) ports and 4x40 GbE ports. It's fixed form factor is very similar to conventional top-of-rack devices, except for two optical interconnect ports that run Plexxi's WDM technology to form a fiber ring that dynamically allocates bandwidth.

Plexxi Switch 1 has a list price of $64,000. The switches ship with all the cabling and optics required for building the WDM fiber ring. A Plexxi Control license costs $5,000 per switch.

Finally, Plexxi is introducing its Affinity Networking APIs, which provide abstractions of the network northbound to orchestration systems like OpenStack Quantum. Plexxi is offering two initial APIs. Workload Affinity API enables external systems, analytical engines and network overlays to communicate with Plexxi Control. The Network Orchestration API will allow Plexxi Control to take information from workload requirements and convert it into instructions on how the network can satisfy them. These APIs will be available next year. Plexxi will also announce a partner ecosystem next year for working with its evolving API set.

WDM: A wide-area technology in the data center

Plexxi uses the WDM-based optical interconnect to build a fiber ring among its switches. With this ring, Plexxi can reconfigure bandwidth between switches on the fly. Telecoms have used WDM to extend the capacity of their physical infrastructure by transmitting data in different colors, but the technology has traditionally been very expensive and static.

"In a typical telco operation, you're assigning each of these lambdas of light to a particular client or path, and it gets pinned up and stays there," 451 Research's Hanselman said.

"We're taking the WDM idea and some very low-cost optical components from other fields, including cell tower backhaul and fiber to the home components, and we're using those to create a different kind of WDM optical mesh," Plexxi's Husak said.

An important element to making WDM work in a data center is SDN, he said. "We could have had this very clever optical architecture and then put a conventional, layered network protocol stack on top of it. It would have been such a densely meshed network [that] it would have confused that protocol stack. We've applied SDN with a centralized controller and a network-scale point of view to look down at the network and this flexible optical architecture and derive the configuration directly from application needs."

Hanselman said WDM allows an enterprise to devote bandwidth between two switches on the network dynamically.

"If you've got a database engine and its storage resources, you probably want those really close together from a performance standpoint," he said. "If your storage array is connected to one switch and the database engine is connected to another, you can now grab one whole wavelength and run that directly between those two points. If you start to get constrained and the database and the storage array doesn't have an available wavelength, you can create a path in the opposite direction on the ring."

Infrastructure as a Service(IaaS) provider CloudSigma has built a Plexxi-based network for a new IaaS cloud based in Las Vegas, which will go into production in early 2013.

"When you run a public cloud where you have 1,000 customers, you get problems when you want to match specific workloads to the network capabilities they need," said Bernino Lind, chief operating officer for Palo Alto, Calif.-based CloudSigma. "[The optical interconnect] does give more flexible and less complex and lower cost networking in those types of topologies that we are looking to deploy. It's basically easier to implement customer cases like high performance computing and big data when you have this deep integration between the networking layer and the software layer with the cloud layer for virtual machines and VLANs. This is really critical when you start to scale out with more and more racks of compute. You're not dependent on the physical layer of switches in the same way you would be with what I'd call generation 2000 switches."

Let us know what you think about the story; email: Shamus McGillicuddy, news director.

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