Sunday, July 22, 2007

Seamless roaming or How to get work done in the john

After a lengthy sabbatical, I am back with another wireless post to satiate your appetites. On the heels of Leo's intriguing post about consumer vs. enterprise class products, I thought I would chime in with the wireless slice of the pie and also explain one of the great features to emerge out of the enterprise wireless network- seamless roaming. It is something we take for granted, but a lot of thought goes into ensuring that all the employees stay connected to the wireless network as they roam around the campus and move from access point to access point.

Now some of you are scratching your heads and saying "I can do that with my current wireless network in my house and roam all the way to the backyard!" While that is true, and impressive, you aren't really "roaming" in the wireless sense. You might be physically roaming, but you are still connected to the same AP. In your office building, you might be connected to one AP near your cube, but when the meeting starts and you enter the conference room, you are connected to a totally different AP. If you notice, your computer jumped to an AP that had stronger signal- but you wouldn't notice if you had a cetrally managed wireless control system, whose job it is to manage all the APs and pick up wireless clients seamlessly as they move. Why is this important? Well, if you were to lose the connection to the network everytime you moved around the building, then things just wouldn't be working out very well. Soon, frustration would set in, and everyone would be complaining that they can't get any work done because the wireless network is so terrible. If you would like, here is an experiment to try at your home:

Set up two routers in different parts of your house and make sure that they cannot "see" each other. You should not be able to get any wireless signal where you are setting up the other AP.
Give them both the exact same parameters and start closest to one AP. When your computer associates to that AP, start to move towards the other AP.
As you get closer, you will notice that your computer drops off and has to reassociate to the other AP. You have lost the connection to the first AP and have started a whole new session.
No seamless roaming for you!


In the corporate world, this would not work and IT departments spend lots of time making sure that there is wireless capability everywhere in the building. Even if you have hundreds of access points, unless you have a way to have them talk to each other then you will not be able to seamlessly roam. It is a critical part to the wireless network and along with the site survey should allow you to provide your users with a level of service that rivals that of the wired network.

You might be asking "Why is this important enough to write about? Let's talk about security or Pam Anderson!" The simple reason is that one huge application of roaming is the Voice Over IP. As Wi-Fi phones become ubiquitous in offices and warehouses around the world, seamless roaming is going to take on a more important function in the wireless network. In order to maintain a jitter-free voice connection, you must have a sub-50 milisecond hand-off from AP to AP. There is no time for a disassociation and a reassociation since the call will be dropped. The client will look for the strongest signal and the network has to be able to accomodate that move from one AP to the other without dropping any packets. Everyone knows how embarrassing and frustrating it is to be on their cell phone and have the call drop while you are in the middle of a business meeting.

In order to ensure seamless roaming, it is important that a centralized wireless network be implemented in the organization, not only for management purposes, but because by allowing the wireless controller to manage all the APs, it will be able to handle the sub- 50 milisecond roam that needs to occur to ensure connectivity remains. We will explore the differences between the centralized and autonomous solutions in another posting, but for now be aware that the idea of seamless roaming is the one thing that can dramatically affect productivity in the workplace....along with your ability to work in the john.

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