The cost of scaling Wi-Fi capacity

Centralized backplane support could be big cost factor, depending on vendor

Industry analysis by expert Joanie Wexler, plus links to the day's wireless news headlines

Wireless LANs rarely allow for simple direct cost comparisons. In addition to variable pricing structures among vendors, one reason is that product architectures differ. That means some systems have different components than others. So how can you compare them, tit for tat?

To be honest, the situation isn't too bad so long as you are looking for basic data coverage across a given area with no per-user throughput guarantees. What gets the mathematical grey matter really pumping is comparing prices when designing for capacity and minimum per-user throughput. You might do this, for example, if you have begun regularly running a multimedia environment with streaming media and want each user to have a certain level of experience at any time or for there always to be capacity available for voice.

The design of a WLAN system dictates the number of network elements (and corresponding software licenses) required to achieve desired coverage and capacity levels. So some systems simply require more infrastructure than others.

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Wireless LANs rarely allow for simple direct cost comparisons. In addition to variable pricing structures among vendors, one reason is that product architectures differ. That means some systems have different components than others. So how can you compare them, tit for tat?

To be honest, the situation isn't too bad so long as you are looking for basic data coverage across a given area with no per-user throughput guarantees. What gets the mathematical grey matter really pumping is comparing prices when designing for capacity and minimum per-user throughput. You might do this, for example, if you have begun regularly running a multimedia environment with streaming media and want each user to have a certain level of experience at any time or for there always to be capacity available for voice.

The design of a WLAN system dictates the number of network elements (and corresponding software licenses) required to achieve desired coverage and capacity levels. So some systems simply require more infrastructure than others.

Fortunately, a number of Wi-Fi vendors make figuring out the AP part of the equation pretty easy with automated site survey tools. You literally circle an area on an online floor plan, tell the system the minimum capacity you want there and -- voila! -- the system tells you how many APs you need and where to install them. Multiply the number of APs by the per-AP cost and you know the cost of that part of the environment (not including discounts, the negotiation of which is a whole other discussion).

However, some suppliers require WLAN controllers while others don't. Most relevant, some controller-based vendors require all data traffic to be backhauled to the controller for forwarding. In this case, and because controller backplane bandwidth can't be shared in non-clustered environments, you might have to add controllers to accumulate the aggregate, concurrent throughput support you want.

Let's say you wanted each of 1,000 users to have 10Mbps of WLAN throughput available consistently, for example. That's 10,000Mbps, or 10Gbps you'd need to support concurrently. Centralized 802.11n vendor controller backplane throughput ranges from 2G to 8Gbps, though some can be revved up using acceleration modules (for a cost).

But you can see that in such a centralized scenario, you might need anywhere from two to five controllers when designing for capacity. And that means paying for all the associated licenses, bells and whistles, too.

Read more about wireless & mobile in Network World's Wireless & Mobile section.

Joanie Wexler is an independent networking technology writer/editor in Silicon Valley.