May 17, 2011

What is a Wi-Fi controller, and do I need one?


Already answered here, and quite well, is the question of what a wifi/wireless/ap controller is.  The question of "do I need one" can be answered with the question of "do I have more than one wireless access point."  If the answer is yes, then in today's networking environment you need a controller.  Not as much for the central point of management, which is really a convenience and a cost factor, but for seamless coverage throughout your network.  Consider wifi and your smart phone.  You have an access point upstairs, downstairs, perhaps in the basement, and maybe one for the back yard.  You have set up your phone to take advantage of google talk over your wifi network.


Now you get a phone call and you want to walk around.  This means that one of the access points needs to function as a controller or that each access point must funtion as a peer in a manner that allows for one access point to talk to another and say, "I have a device headed your way, can you please take over?"  and the other can respond with, "taking over in 3.... 2.... 1...."


The problem is that the home/SOHO market doesn't really have a solution to fit, so while the need is there, the product does not yet exist.  Consider the scenario of four access points above.  The most cost effective solution I have seen to date would run into nearly $1000 US with only two running into about $500 US.


Netgear has a software only controller that is priced between $40 and $100, but the access points that will work with it are either A/B/G or around $200 a piece.  More of a lower tier SMB offering than a SOHO one.


The truth is that, in spite of the increasing number of SOHO businesses, there are few offerings designed for that market place and currently no wireless controllers as of this writing.


To summarize, you probably need one in today's environment, but it does not yet exist unless you want to spend $500 and up.


Also you need to consider the size of your business and its needs. If you're a small business running out of your home, you probably don't need a Wi-Fi controller. If you're a small business but handle a significant load of work with multiple points of access, it may be cost-effective to deploy a Wi-Fi controller.


This is a great and very common question, and one that I hear at least every week. It's also important to understand the answer, as controller implementation serves as a primary differentiation in enterprise-class systems (the other being management features). Let's start with the big picture. The purpose of a WLAN system is of course to move data in essentially the same manner as a wired LAN. But there's a much higher degree of variability in the architecture of WLAN systems and solutions, and we therefore have developed a model, based on the concept of planes, to describe the internal functions of a given WLAN architecture. These planes are as follows:


Data Plane – This describes how data moves within the WLAN. The biggest question is whether data from an access point (AP) can be forwarded directly to its destination, or whether this data must flow through a separate physical element, called a controller.


Management Plane – This describes how the system is configured, monitored, and how many other required functions are implemented. The management function is almost always centralized in a single location, even for large, distributed, and multi-vendor solutions. The point of residence can also be in a controller, or a separate appliance or server.


Control Plane – This plane can be thought of as the “operating system” of the WLAN, executing policies defined by the Management Plane and optimizing the flow of data in the Data Plane. And, you guessed it, such functionality also often resides in a controller (which can even be virtual in some products), or can be distributed across the APs. Controller functionality can also move among elements in some implementations.


We can probably agree that the Data Plane should be as distributed as possible, and that the Management Plane must be centralized. So it's the Control Plane that presents the greatest opportunity for controversy, as it can be fully distributed and implemented in an AP, reside in a server, or, again, live in a separate box, the controller. While vendor arguments are plentiful and often persuasive, there's not enough empirical (based on appropriate benchmarks) or analytical (the results of mathematical models of system behavior given specific configuration and loading) to provide a definitive argument either way. One can certainly make the argument that a controller adds cost (and that additional or redundant controllers may be required to handle certain loads and/or provide fault tolerance), but one must consider the total cost of a given solution, not the cost of individual elements. And one can make the argument that a controller-based implementation provides a more global view of system condition and behavior, and thus could yield higher performance especially over time – but, again, there are no definitive studies (yet) one way or the other. The degree of architectural diversity around this question is indeed significant, and we expect to see additional architectural variability before any definitive solution is recognized as such.


Do you need a controller? Much depends upon what your supplier proposes. Careful analysis of the arguments presented by vendors during the purchasing process and appropriate benchmarking tests based on local requirements are the only guides at present.

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