Wireless LAN coexistence at Interop

by Matthew Gast

Related link: http://www.interop.com

Building a large-scale wireless network is challenging. Large scale gets much worse when you have to contend with the problems of unlicensed spectrum. I'm sitting on the exhibition floor right now at Interop, and I've chosen to use a wired Ethernet connection because it is performing much better than the wireless network. In addition to the sponsored show network, there are several exhibitors building their own networks. In a first for a trade show I've been to, though, there are signs with solid network engineering advice:


Although there is no legal or regulatory way to control the use of unlicensed spectrum, there is technical authority behind the recommendations. For the most part, my extremely brief spot checks with an analyzer have found them to be followed. There is no reason not to use the lowest power settings--most exhibitors don't need to go beyond their booths, which just aren't that big. Staying on the three mostly non-overlapping channels is also solid advice. Just because 802.11b/g gives you 11 channels (in the U.S.) doesn't mean that you can use all eleven. When lots of networks spring up on all the channels, everybody's throughput suffers. Three channels might be slow, but it will be faster than using every channel.

(As an interesting aside, I found a forbidden configuration on the floor. In 2003, an engineer from a very well-known networking company had put his demonstration on channel 14 because "the rest of the channels were too crowded, and it wasn't fast enough to use the allowed channels.")

If you want better speed and the 2.4 GHz band used by 802.11b/g is a mess, there's a great solution: 802.11a. The sign shows that four channels were reserved for 802.11a use by exhibitors, which I would think makes channel layout very easy.