Software-defined networking (SDN) startup Plexxi divulged details of its architecture Wednesday, describing how its optical-ring layout can make a data center better suited for cloud services.

Light Reading outlined Plexxi's details back in September. The startup goes beyond pure software; it's offering top-of-rack 10Gbit/s Ethernet switches and a controller architecture to make them all SDN-like.

How's it all work? Let us remind you of what we discovered in September:



More specifically, Plexxi's switches are connected in a fiber-optic ring. When two items in the data center need to be linked (what Plexxi calls an "affinity"), the network ring configures accordingly. Plexxi refers to this as moving the network to suit the workload, rather than the other way around.

"We wanted to go out and create an actual network that was fully definable by software," says Mat Mathews, Plexxi's vice president of product management.

The difference might sound semantic, but it means there's no external application, sitting atop all the software, that tells the network what to do.

It also means the network has no tiers and none of the leaf/spine architecture that data center people talk about. With vendors boasting about how flat they can make the network, Plexxi seems to have found a way to be the flattest of all.

"Other networks just use protocols to make the network look flat," Mathews says.

It's all run by a controller that's centralized but also includes a federated piece distributed to each switch. The setup is similar to the way OpenFlow gets deployed, but the inner workings are very different (and no, OpenFlow itself isn't supported yet). Plexxi uses algorithms and a global view of the network to decide how to configure the network.

In other words, rather than programming route tables, the controller looks at the needs of the workloads and calculates how the network ought to be getting used. Some of this can even happen automatically.

This is where it's going to get tricky for Plexxi: To get partners involved, the company has to bend them toward this way of thinking. Partners might be used to using APIs for issuing commands to pieces of software. Plexxi calls for "affinity APIs," where a tool tells the network what it cares about -- high bandwidth or ample storage, for instance -- leaving the network to hash out the specifics.

The ring setup does create extra latency, because Plexxi can't avoid the speed of light. Its setup isn't targeting high-frequency traders that need to shave nanoseconds off of a transmission.

The entire Plexxi collection is shipping, and the company has a couple of customers in production, Mathews says. One is trying to offer a premier cloud service where workloads are guaranteed to be a maximum number of hops apart on the network. Another is offering an elastic storage service based on big disk arrays; Plexxi's gear treats each customer's chunk of storage as a workload to be mated to the rest of the customer's virtual network.

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— Craig Matsumoto, Managing Editor, Light Reading