Showing posts from February, 2013

Adjacent Channel Interference

I was inspired to try a bit of experimentation following Keith Parsons' recent WiFi stress testing sessions, where he conducted testing on a number of vendor APs to observe at what point they collapsed in to a heap  due to traffic throughput. I can't carry out anything as grand or detailed as Keith (I don't have his knowledege, brains or resources!), but I thought it might be fun to test some de-facto rules around the use of the 2.4GHz band for WiFi. In summary, due to the bandwidth requirements of WiFi equipment, it recommended that the spacing of at least 22MHz is allowed between the channels being used in the 2.4GHz band. This is required for the bandwidth requirements of the older DSSS modulation scheme. The newer OFDM modulation technique requires only 20MHz of space, but for reasons of backward compatibility, the 22MHz rule persists. The band itself is sliced up in to 11, 13 or 14 channels depending where you are in the world. Each channel is 5MHz in width, as

Aerohive AP121 Alternative Power Supply

Got yourself a free Aerohive 121 AP after a recent training course or webinar? Got it home and found it's got no PSU!? Yeah, annoying isn't it... Get yourself one of these 'bad boys' off Amazon - bought one this week and works a treat! Disclaimer : if it blows your AP up don't blame me...mine certainly worked OK :) *** Update 11th October 2013*** Works well for an AirTight C-55 AP too!

Which iPads Are On The Network?

Sometimes you can walk on to a customer site and the customer may have iPad devices using the WiFi network. They may also have a range of different models, so that it is difficult to perhaps know the WiFi support capabilities available among their devices. In summary, to-date all iPads support 802.11 a/b/g and 802.11n on both the 2.4GHz and 5GHz bands. The 802.11n support is exclusively single stream, but the channel width that can be used has changed with recent models. Both the 4th Gen. iPad and iPad Mini support 40MHz channel widths on the 5GHz band. It is quite difficult to determine which version of iPad you have just by a cursory glance at the device. A very good way of determining the device type you are working with is to check the model number on the back of the iPad. It's a little tricky to read due to the small size of the etched-in font, but with a bit of a squint, you can just about see it. Here is a picture taken from the rear of my own iPad 2: By using t