I would like to know how to setup wireless frequencies when deploying more than one access point.
Let's suppose I have two access points with the exact same wifi security settings and SSID, meant for "fast roaming". What frequency should both devices have? More exactly, should their frequencies (GHz) be different or should they be the same?
Now let's suppose I have one access point and one repeater/extender/rangebooster. Should the repeater have the same frequency as the access point or should it be different?
I'm asking this because searching the web gave me all types of answers. Some say that I would have to use the same frequency and others say that they should be different, to avoid interference.
I'm guessing that in the case of a repeater "it makes sense" that the frequency should be exactly the same. However, in the case of 2 access points, they may work better if the frequencies don't match.
The questions you are asking can have a broad range of answers depending on whom you ask quite possibly. I am not going to say all the answers are correct, but most have some merit to them. Keeping that in mind here are my answers to your questions.
First the issue is not just about the Frequency, but also about Channel with-in that frequency. Depending on what country your in depends on the actual channels available, but my answer is still applicable. I usually try to move clients to the 5Ghz frequency (802.11a) because there are fewer devices in that spectrum, less interference, and more channels (36, 40, 44, 48, 52, 56, 60, 64, 149, 153, 157, 161 in the US). The benefit of this is that it allows you to put more access points in a given area without creating Co-channel intereference, the downside to this is that not all client devices support 5Ghz (802.11a) so in this case you need to opt for the 2,4Ghz Band (802.111b/g) which only has 3 non-overlapping channels (1,6, & 11 in the US). On the 2.4Ghz side it is highly reccomended to only use these three channels; so this is limiting when you need to put 4 access points in a small area where each AP can hear the others really well; this is where design,planning and channel planning come into play. The last consideration here is the overall coverage area, 2.4Ghz has a larger coverage cell for 2 reasons: 1) A 2.4Ghz radio wave travels farther and penetrates obstructions better than higher frequencies, 2) 2.4Ghz has the potential of having a higher transmit power - 802.11b is capable of a max transmit power of 100mw from the AP for a total max EIRP of 30db or 1 Watt.
So with that out of the way if you have two AP's configured identically you should have them on the same band either 802.11a or 802.11b/g to permit the most seemless roam, since many clients devices don't always smoothly change bands; but in doing so the AP's need to be on different channels.
If you are setting up one access point and one repeater then the repeater needs to be on the same band and channel as the access point otherwise it is incapable of repeating the signal since it won't hear it.
I hope this helps, if it does feel free to rate it.