Say for example, the past several years you’ve been gradually deploying WAPs throughout your network infrastructure to the point of now warranting the use of a wireless controller to reduce management overhead. You never expected your wireless infrastructure to have grown so large, thus many of the WAPs currently deployed do not support a wireless controller and you’re now considering replacement of your entire wireless infrastructure.
Unfortunately, the cost associated with updating or replacing an entire wireless infrastructure or even the costs of a controller alone often outweigh the management overhead reduction causing the project to be put on hold or rejected.
The use of a wireless controller typically requires that you’ve had some type of WAP standardization protocol in effect so that the WAPs you’ve been deploying are through the same vendor and the same model or family. Even then, it’s usually only those identified as “enterprise grade” that include support for a controller often leaving IT professionals out of luck.