Startup PLUMgrid Inc. launched its software-defined networking (SDN) platform Tuesday, casting its vote with the overlay model favored by Nicira Networks Inc. rather than the controller model favored by the likes of Big Switch Networks and the OpenDaylight consortium.

Like VMware Inc. (which owns Nicira), Plumgrid is worried that the controller model won't scale. "There are still questions about OpenFlow, with its forklift upgrade," says Pere Monclus, Plumgrid's CTO. "The most stable structure is to keep the fabric simple and put all the features in the overlay."

The Plumgrid Platform consists of software running on ordinary servers. It does rely on an underlying physical network, but it doesn't matter what kind. It can be Ethernet, IP or even InfiniBand. Plumgrid software called IO Visor connects those elements into arbitrary topologies, creating an overlay network, and it can shift that connectivity around the data center as needed.

The importance of not caring about the physical-network protocol is that Plumgrid can create an overlay across multiple environments. If your data center and your public cloud don't use the same protocol, Plumgrid can still build overlay connections that bridge both sides.

The platform has gotten some attention from AT&T Inc., which has test-driven the Plumgrid platform at the AT&T Foundry (innovation lab) in Palo Alto. The carrier could use Plumgrid for public cloud services, or it could even apply the technology internally to its own data centers.

Plumgrid picked this approach two years ago, before SDN had become white hot, CEO Awais Nemat says. The focal points were automated changes to the network and automated provisioning of connectivity.

A function called the Director is in charge of all the overlay activity -- creating these virtual connections, for instance. But it doesn't have a hand in the actual processing of packets, which is one main contrast between the overlay model and the controller model.

The controller model tends to require packet flows to contact a controller. "We have moved that controller out of the way," Nemat says. Plumgrid and Nicira believe this helps the virtual network grow to a bigger scale.

Plumgrid makes its network programmable via APIs, because that's what everybody does these days. It's also lined up partners whose functionality can be connected into the network or even loaded as virtual appliances. There are 13 of these, most of them covering Layer 4 through 7 territory; examples include Check Point Software Technologies Ltd., Citrix Systems Inc., F5 Networks Inc., Ixia and Palo Alto Networks Inc.

Eventually, a Plumgrid software development kit (SDK) will let other companies create their own APIs for the Plumgrid Platform. That SDK isn't publicly available yet.

— Craig Matsumoto, Managing Editor, Light Reading