<div dir="ltr"><div><div>I would also point out that if you have 20+ clients at a location you should consider using commercial or enterprise-grade access points.<br><br></div>Companies like Aruba Networks make APs which each can contain multiple radios, and support handing off clients between radios and access points depending on available load.<br>
<br></div>This functionality does not come cheap. The last time I talked to someone from Aruba at a trade show their cheapest access point that could self-configure itself with others on the same network (to avoid paying for a centralized controller) was a few hundred dollars per AP.<br>
<br><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Feb 7, 2014 at 5:22 PM, James Cameron <span dir="ltr"><<a href="mailto:quozl@laptop.org" target="_blank">quozl@laptop.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On Fri, Feb 07, 2014 at 09:29:46AM -0500, Tim Moody wrote:<br>
> [Don't forget that James wrote:]<br>
<div>> >If you choose to deploy with interfering channels for some reason,<br>
><br>
> Many routers support narrowing the band around channels.<br>
<br>
</div>No, it is more correct to say that many routers support widening the<br>
band around channels, to achieve a higher data rate.<br>
<br>
Consider a spectrum; the X axis is frequency, the Y axis is signal<br>
strength. The bandwidth of the transmitter is a curve shaped like a<br>
hill. The bandwidth of the receiver is another curve. The channel<br>
selects the centre X position of the hill.<br>
<br>
The certification defines an area as a rectangle, and routers and<br>
devices pass certification based on spectrum analysis of the<br>
transmission, not of reception.<br>
<br>
There is always an interference between all channels, but the standard<br>
defines the limits on the interference in quantifiable terms. But<br>
these can be translated simply as:<br>
<br>
- the interference between 1 and 11 is trivial,<br>
<br>
- the interference between 1 and 6 is low,<br>
<br>
- the interference between 1 and 2 is significant.<br>
<br>
- the interference between 1 and 1 is extreme.<br>
<br>
The interference causes backoff, where a node that would transmit<br>
waits a bit longer, and collisions, where a node receives a corrupted<br>
transmission. Both of these act to reduce total system data<br>
bandwidth.<br>
<br>
Given fixed channels, the interference increases as the distance<br>
between the interfering devices decreases.<br>
<div><br>
> Are you of the opinion that this is ineffective and that there is<br>
> always a 5 channel overlap?<br>
<br>
</div>I'm of the opinion that widening the bandwidth used around channel 6<br>
will impact channel 1 more.<br>
<div><br>
> Of course, we do not always have control over the entire<br>
> environment, so 1, 6, and 11 may already be taken and we have no say<br>
> in the matter.<br>
<br>
</div>It is more complex than that. While you might see another access<br>
point on a channel, you might still be able to deploy your own access<br>
point on the same channel, and the two access points will cooperate in<br>
a limited fashion. They listen before they transmit. So too do the<br>
laptops. The TCP/IP rates are reduced.<br>
<br>
If you are faced with 1, 6, and 11 all taken, and you wish to run<br>
one access point, then find which of 1, 6 and 11 have the least<br>
received power, and use that.<br>
<br>
If you are faced with 1, 6, and 11 all taken, and you wish to run two<br>
access points, then find which two of 1, 6 and 11 have the least<br>
received power, and use them.<br>
<br>
If you are faced with 1, 6, and 11 all taken, and you wish to run<br>
three access points, use 1, 6, and 11.<br>
<br>
If you wish to use a channel outside 1, 6, and 11, then you would do a<br>
more complex survey, to find the channel with the least received power<br>
for both your access point and your devices. Then measure the TCP/IP<br>
rates you get.<br>
<br>
That survey is invalidated every time someone walks in with an Android<br>
or iOS phone or a portable hotspot; these act as an access point.<br>
<div><div><br>
--<br>
James Cameron<br>
<a href="http://quozl.linux.org.au/" target="_blank">http://quozl.linux.org.au/</a><br>
</div></div></blockquote></div><br></div></div>