"They're almost entirely research and development," says Jason Needham, F5's vice president of product management.

In fact, F5 isn't fully disclosing its plans for the startup it acquired Monday, beyond the fact that it intends to merge LineRate's software into the BIG-IP platform.

What F5 is saying is that the deal fits with the company's broader approach of looking at SDN from the upper layers.

"You can take a network-up approach, where you solve for the network layer first, or you can take a service view [and move] down. F5 has always contended it's easier to start with the most intelligent layer," Needham says.

This is not particularly shocking, given that F5 inhabits those upper layers. For a couple of years, the company has been circulating the idea of an application control plane, a way to program the network at the service layer. That's the shade of SDN the company wants to emphasize.

"You sit above the network fabric and add a layer of application-fluent services. You have to understand the applications and be stateful if the applications require that, and also be dynamic," Needham says.

The idea would be to deploy very specific, targeted services around the network, says Lori MacVittie, F5's senior technical marketing manager.

LineRate's software inspects traffic at the application layer, allowing for traffic management or policy decisions based on the results. F5 isn't discussing specifics about what makes LineRate so allegedly useful, though. The startup has made "breakthroughs in terms of software scalability" and has a fresh approach toward making the network programmable, Needham says.

LineRate was founded four years ago, before "SDN" was all over the tech-blog headlines. As with a lot of companies, whether LineRate counts as SDN is debatable, as Tom Nolle, prinicpal analyst with CIMI Corp., points out on his blog. (He also takes issue, understandably, with the "Layer 7+" term that LineRate uses.)

But LineRate can certainly be folded into an SDN architecture, presuming one is OK with using the "SDN" term to apply to higher layers.

"F5 is kind of framing this within an SDN context, and there are technologies they're going to get from LineRate in terms of manageability and cloud orchestration: the actual LineRate OS and the fact that it's got its own streamlined TCP stack, which helps it get the scale and performance on COTS [commercial, off-the-shelf hardware]," says Brad Casemore, an analyst with IDC.

The deal shows F5's thinking is in the right place. Casemore sees F5 preparing for a world where network services are more closely coupled with applications, and where those services have to move with the virtual machine that's running the application -- all of which means the upper layers, like routing and switching below them, will require an even heavier dose of software.

"They're not going to be disruptive with a hardware-appliance approach," Casemore says.

For more

• F5 Buys Layer 7 SDN Specialist
• F5 Gets Into Policy Enforcement

— Craig Matsumoto, Managing Editor, Light Reading