03/18/11 16:00
Wireless is easy to deploy (well there are some exceptions to this), hard to do well. The air is a shared medium. Some of you old schoolers, hikers, mountain bikers understand walkie talkies and we know that RF is a shared medium. “Push to talk” is essential on any medium, but is especially problematic in a more limited spectrum such as wireless. We all know about switches and how superior they are to hubs, but in the air, it’s a hub and not a switch. We begin therefore with less spectrum to squeeze into. While in the US there are 11 channels (channel 12 and 13 existing in other geographies) available in the 802.11b/g 2.4 GHz space, that’s not true. Out of those 11 channels, only three (1, 6 and 11) do not overlap, and of course, not overlapping means then not using channels, 2, 3, 4, 5, 7, 8, 9 and 10. True, things are better in the 802.11a 5 GHz spectrum. 802.11n adds multiple-input multiple-output (MIMO) and 40 MHz bandwidth per channel, but this takes up even more of the 2.4 GHz range. Fortunately 802.11a can also use the 5 GHz frequency, but that assumes the client can use it.
Those iPhone 4s are really cool, they don’t use the 5 GHz range, that makes life really tough. Quoting someone else, that means that iPhone 4 has 802.11n but not the “awesome” 802.11n.
There are lots of tricks different manufacturers use. One professes the advantage of using a single channel across all APs (Access Points); another talks about use adaptive channel management; another talks about beam forming; another about beam steering; still others about techniques for prioritizing traffic. Some use small APs in a larger mesh, others use large UFO looking APs called arrays.
Guests are handled a variety of ways including captive portals and various mechanisms to enable those. Think of a hotel signing-in experience and you get the idea.
Management approaches vary wildly as well. Some use centralized controllers, some use cloud based, some use hive based smart APs, some offer both cloud and controller based. In terms of controlling access to the networks, approaches vary there as well whether it’s a simple physical connection, VLAN based, tunneled back to a controller or the ability to split tunnel. Mesh approaches are used too in order to address connectivity when a LAN wired connection is lost or cannot be made to an AP and a wireless backhaul needs to be used.
When it comes to prioritizing traffic whether it’s for voice, video or data, different approaches are used there too. At the end of the day, it’s about managing the wireless spectrum and getting a strong predictable signal (with minimal noise and interference) to the client. The best controller is no match for a problematic air space.
So it’s about really understanding what your current air spare and spectrum usage looks like and finding a solution that can work best in your current air space, physical layout, and for the client device connection capabilities and needs that you have. Wireless cannot be magically solved by just deploying technology and neither is it a set and forget approach. It changes due to changing physical environments (think boxes moving in a warehouse, doors opening/closing, etc.), changes in the spectrum (as people and firms in your shared air space add and change their channel usage), evolving standards and client endpoint drivers and capabilities.
I use and offer four different vendor offerings for wireless, each offers a unique solution for certain environments.