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Branch office WAN optimization appliances: Does packet flow matter?

Depending on how you expect to use your branch office WAN optimization appliance, the number of simultaneous packet flows it supports may be a crucial or trivial part of your purchase.

When looking at wide area network (WAN) optimization products, the item on the spec sheet that catches your eye...

first is most likely speed. But what about packet flow capacity? Depending on how you expect to use your branch office WAN optimization appliance, the number of simultaneous flows it supports may be a crucial or trivial part of your purchasing decision.

"You don't generally need a ton [of packet flow capacity]. It depends on what you're doing in the branch. If you're a brokerage firm and you're doing a lot of real-time quotes, you need a lot of flows," said Zeus Kerravala, distinguished research fellow at Yankee Group. "You have to really do your own capacity planning and have a good understanding of where, in fact, [traffic] is going."

Data center WAN optimization products clearly need to juggle and optimize hundreds of thousands of packet flows -- not just for application acceleration but also for storage area networks and disaster recovery plans.

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But to optimize a few branch offices with 10 or 15 users each -- where the budget may be tighter and the decision more of a judgment call than mission critical -- determining the right packet flow threshold gets a bit murkier. It may be hundreds or thousands of packet flows, depending on the applications the branch is running, Kerravala said.

"It is tough. All these vendors give you a different way of doing it," he said. "[But] you can't really build a good WAN roadmap without building an application roadmap to understand [your needs]."

Few branch office WAN optimization appliances are alike, given the variables, according to Apurva Davé, vice president of product marketing at Riverbed Technology.

"Some folks have really sized their appliances based on bandwidth; others have really sized them based on TCP connections," Davé said. "Sizing really depends on what your particular needs are because, in some cases, you might have really high bandwidth needs and really low connection needs or vice versa. It's rarely a one-size-fits-all challenge."

To get the most out of a branch office WAN optimization appliance, Davé recommends that networking pros look beyond just the numbers.

"Flow is just one part of it," he said. "Assessing the number of flows is good. It's important, but what's more important is how those flows go across your network and where they are going. The architecture of which WAN optimization device you choose will matter greatly."

When packet flow capacity doesn't factor

Although he knows that each of his 30 branches tend to have 300 to 400 flows open at any given time, Matt Simmons, IT infrastructure manager at Golf Savings Bank of Mountlake Terrace, Wash., doesn't consider packet flow capacity a make-or-break feature for his branch-based WAN optimization purchases.

You can sit there and talk about flow numbers, but at the end of the day, if I can't go to my users and see if life has been better for [them] ... it's hard to justify making those investments.
Matt Simmons
IT Infrastructure ManagerGolf Savings Bank

"I think it's more of a marketing thing," Simmons said. "It all comes down to the user experience. You can sit there and talk about flow numbers, but at the end of the day, if I can't go to my users and see if life has been better for [them] on the network since we put the technology in, it's hard to justify making those investments."

Instead of monitoring packet flow, Simmons takes a slightly less technical approach to achieving his goal -- he dispatches his operations teams to the branches with stopwatches and the WAN optimization products ready for a bake-off.

"Literally, they will go out to a branch with a stopwatch and watch people pull up a webpage, run a core application, do just basic user functions they have to do day-to-day and look at the exact metrics of what kind of time those things take," Simmons said. "We can get some really hard numbers [by doing] this."

Small branch office WAN optimization appliances can be big on packet flow

At the lowest end of the offerings, Riverbed's Steelhead desktop-sized 250 series can optimize between 30 and 200 simultaneous TCP connections at 1 Mbps, depending on the model. The two models in its 550 series, meant for midsized offices, support 300 and 600 flows, at 2 Mbps.

Silver Peak, which has made its name optimizing links between data centers, recently released its 1 RU version of the branch office WAN optimization appliance, the NX-1000, which boasts the capacity for 8,000 simultaneous flows at 4 Mbps.

Similarly, the low end of Blue Coat Systems' PacketShaper appliance, the 900 series, supports up to 7,500 simultaneous flows at 2 Mbps.

A 30-person branch office is likely to generate about 900 flows at any given time, according to Damon Ennis, vice president of product management at Silver Peak. But it's better to have excess flow capacity than to be short on it, especially if the branch is a call center operating entirely on voice over IP, Ennis said.

"We've got way more than enough to handle any reasonably sized [branch] office," he said. "If you put in an appliance [that supports] only a small number of flows, you don't get the benefit of acceleration…. The worst thing is to run out of [packet flow capacity], because you're going to have upset users."

Following customer requests for a physically smaller and quieter branch office WAN optimization appliance, Silver Peak sought to downsize its then-smallest WAN optimization product, the NX-2000, Ennis said.

"Our previous low-end appliance is 64,000 flows, which is way overkill," he said. "But it was a pretty big box and it was quite loud, which meant people couldn't put it in cube-ville. We also lowered our flow counts, but we also wanted to keep them high enough that [packet flow capacity] would never be a concern."

Let us know what you think about the story; email: Jessica Scarpati, News Writer

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