The channels are the different radio frequencies that the Airport can operate at. They shouldn't make a major difference unless there are other routers nearby trying to operate on the same channel. Typically, the only ones worth using are 1, 6, and 11, due to overlap issues.
I created a roaming network by tying two AEBS together with an ethernet cable, from LAN port to LAN port, as shown in the manual. They mention the channel 1,6,11 thing, and that you want at least 5 channels of separation. So I chose 1 and 11 for my two AEBS.
So far so good. But, what about the 5GHz channels? My choices were something like 36-54, and 149-162 (or whatever the exact numbers were). Previously my first AEBS was in automatic mode and chose 149. So I kept that and for the second one, chose the largest number (162 or whatever it was).
But, what's the deal with the lower range of numbers? And, doing searching online I also read that the 5GHz band also has 1-11 as well.
Can anyone explain this some more? I mean, would it have been a bad idea to use 36 and 162 (or whatever the upper one was)?
Everything is working great, so it's mostly curiosity on my part--I just like to know about these things.
Also, I should mention that previously I had extended the network wirelessly (WDS) and it was a disaster. I read that the throughput goes down like 1/(2^n) where n = number of wireless clients on the 2nd router. And well, I think it's true. When I was connected through the router that extended the network wirelessly, and when one or more other people were also on that router, it was painfully slow. It was not fun to drill all the holes to run the ethernet cable, but it was definitely worth it.
I did some research and found the deal with 5GHz 802.11n channels. It is surprisingly difficult to find ANY information on the subject!
So . . . check out this link for the channels:
5Ghz channels & bonding
Note that if you count up the number of channels you'll find more than 24, but there are only 24 non-overlapping 20MHz channels, due to 34-48 being only 10 MHz apart. If you go with the "use wide channels option" this will reduce you from 24 to 12 non-overlapping channels, which is still loads better than 2.4GHz's 3 20 MHz wide non-overlapping channels, or TWO 40MHz channels (with bonding).
Now, the story doesn't end there! Turns out that the confusing numbering system refers to different power limitations that are imposed on the different bands. Check out
this link and in particular on the following from it:
There are now four bands in 5 GHz channelized for 802.11 in the US, although they're numbered somewhat strangely. In brief, there is total of 555 MHz across 23 channels in 802.11a/n. The lower four are indoor only; the higher 19 are indoor/outdoor. The lowest four (5.15 to 5.25 GHz) can have 50 mW of output power, the next four (5.25 GHz to 5.35 GHz), 250 mW; the next 11 (5.47 to 5.725 GHz), 250 mW; and the top four (5.725 to 5.825 GHz) up to 1 W. (There are further restrictions on 5.25 GHz to 5.725 GHz in terms of detecting and avoiding stepping on military radar transmissions, which share those bands. And the 802.11a spec specifies 40 mW/200 mW/800 mW instead of 50, 250, and 1,000, just to make it even more complicated.)
There are an enormous number of details about effective output, antenna gain, and so forth, but most of that affects the use of directional antennas and point-to-multipoint outdoor connections, not the use of interior omnidirectional antennas.
Because 5 GHz signals have shorter wavelengths than 2.4 GHz signals, at the same amount of power, they propagate shorter distances. They're also worse at penetrating solid objects. This means that even if you use the top four channels for 802.11a or single-wide channels for 802.11n in 5 GHz, you will only be able to send data less than half as far if that. There are only two double-wide channels possible in that top band.
In the 250 mW restricted range of 5 GHz, you could achieve the same range by using higher power in 5 GHz than in 2.4 GHz. But many of the devices that offer 2.4 GHz and 5 GHz radios don't compensate in 5 GHz by having higher-powered signal output. Thus a device that gives you 100 interior feet in any direction in 2.4 GHz could span less than 50 feet for this reason in 5 GHz. The lack of interference from competing networks could compensate for the shorter distance, however.
So, in terms of setting the 5GHz channels manually, it looks to me like you're best bet is to chose 149-161 (or 165--although, this seems to be missing from some attributions/hardware). However, note that if you're using 20MHz channels, that all of these are non-overlapping. If you're using wide channels, you'd go with 149, 157, 165. The reason to chose the uppermost ones is that they can go up to 1000 mW/m of output power and have dynamic allocation (or something like that--not sure what that means right now). Plus, on its own, in automatic mode, the AEBS seems to go for 149 or one of those uppermost channels.
Personally, I'm thinking that putting all basestations in automatic mode would probably work out just fine. I may test this theory out later tonight.
