Keith C. Perry on 1 Jul 2017 15:22:54 -0700

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Re: [PLUG] Guest Wi-Fi

In addition to Brents excellent points the other thing to keep in mind is that wifi... really any low power rf communication system operates best with more nodes running at low powers that with less units running at higher powers.

The physics of rf communications is about antennae (being heard) and not power (how loud you are speaking).

Practically speaking, my rule of thumb is 1dBm / m in open air.  The more units you have, the less power you need to run but the important thing is to tune your wireless network to your particular environment.  Your devices will hear each other better in the long run if you go through an iterative process to get the performance dialed in.

Also note that although 1,6,11 are the best channels to use on 2.4Ghz because they do not overlap at 20Mhz channel widths, ALL channels in the US 5Ghz band DO NOT overlap for 20Mhz bandwidths.  If you can band steer (not a standard thing- some methods work better than others) or generally use 5G you  might have a better experience (it requires its own tuning).

I don't run a dedicated guest net at home but with the Unifi system I can do a guest network (with or without a portal and hard network exception rules).  VLANs could be used as well but in either case the most important thing is to get the physics right of your wifi network.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Keith C. Perry, MS E.E.
Managing Member, DAO Technologies LLC
(O) +1.215.525.4165 x2033
(M) +1.215.432.5167

From: "brent saner" <>
To: "Philadelphia Linux User's Group Discussion List" <>
Sent: Saturday, July 1, 2017 3:20:10 PM
Subject: Re: [PLUG] Guest Wi-Fi

the notion that they won't affect each other if they're on different channels is only partly true. specifically, it's mostly false but can be true under certain circumstances. this is due to channel bleed and signal congestion.

as an explanation, see this model[0]. disregard 12, 13, and 14- those are prohibited under FCC regulations. this represents "channel bleed". have you ever been trying to find a station while listening to the radio, and you get to a certain frequency (let's say, for example purposes, 95.3FM) and you hear two stations at once? then you tune to 95.1FM and hear only one of those stations in crystal clarity, and then tune to 95.5FM and hear the other station in crystal clarity? same exact thing happens on wi-fi, just on a different frequency band. channels 1, 6, and 11 are marked in blue because they're the only unique channels you can implement in a given signalspace if you want to avoid channel bleed. however, that brings me to...

signal congestion. everyone and their mother has some sort of 2.4GHz antenna broadcasting these days. now, because 1, 6, and 11 are the most ideal channels in mixed signalspace, that means that by *factory default* most devices use one of only these three channels (USUALLY ch. 6). the vast majority of consumers don't change their defaults. going back to FM radio above, this is how pirate radio station hijackings would work (does anyone remember those?) - they hop on the same exact frequency another station is broadcasting on, and the stronger signal wins (usually what decides the stronger signal is a balance between 1. distance from a. the broadcast's point of origin and b. the receiving antenna, and 2. the power of the broadcasted signal).

the FCC places restrictions/regulations on signal power for wi-fi.


sent from my toaster.

On Jul 1, 2017 14:44, "Chad Waters" <> wrote:
Yes. Different channels won't interfere with each other. You do need to consider any nieghbors' APs within range though.

I haven't looked at consumer APs in a while: look for a model that supports multiple SSIDs and VLANs and you can do it all with 1 unit.

On Jul 1, 2017 2:01 PM, "Casey Bralla" <> wrote:
On Saturday, July 1, 2017 1:33:56 PM EDT JP Vossen wrote:
> Following up on the "Router Recommendations" email, any thoughts on how
> to do "guest" Wi-Fi at home?
> One idea is to move the WRT54GL to a guest segment and just get a new
> device for the Wi-Fi (with LAN rules) segment.  But that means that
> guest Wi-Fi is really old, which is not a show-stopper, but...  And I
> can see the 2 units interfering with each other, maybe?
> Thoughts?

I've often thought of doing this also.   I think that as long as you don't use
the same (or adjacent) channels on each device, you can have any number of
physical WAPs operating independently.   Just to be safe, I would place them
as far apart as is practical, but I don't think they will hurt each other.


Casey Bralla
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