Re: 802.11 stuff

Rôgêr <(E-Mail Removed)> wrote:

> I'm very used to dealing with 802.11b but not so familiar with faster
> flavors. If I were to open up one access point to users on 802.11b but
> held out another access point for faster users, could that work? I'm
> thinking in terms of getting a 16Mb Comcast connection and would like to
> be able to get higher throughput on at least one AP. In other words, not
> allow slow connections on the faster AP so everyone wouldn't be slowed
> down to 802.11b.

An 808.11g AP has to accept and wait for 802.11b traffic present on the
2.4GHz band. And any 802.11b AP or 802.11b client will not be able to
"see" the 802.11g AP or 802.11g clients or the 802.11g traffic. So the
end result will be slow traffic on the 802.11g AP.

Better would be using an 802.11a AP, which uses the 5GHZ band and does
not interfer with 2.4GHz traffic for your fast connection.

John Navas <(E-Mail Removed)> wrote:

> On Thu, 9 Jul 2009 01:24:31 +0200, (E-Mail Removed) (Axel
> Hammerschmidt) wrote in <1j2kbgm.wrcfmo1gop32cN%(E-Mail Removed)>:
>
> >Rôgêr <(E-Mail Removed)> wrote:
> >
> >> I'm very used to dealing with 802.11b but not so familiar with faster
> >> flavors. If I were to open up one access point to users on 802.11b but
> >> held out another access point for faster users, could that work? I'm
> >> thinking in terms of getting a 16Mb Comcast connection and would like to
> >> be able to get higher throughput on at least one AP. In other words, not
> >> allow slow connections on the faster AP so everyone wouldn't be slowed
> >> down to 802.11b.
> >
> >An 808.11g AP has to accept and wait for 802.11b traffic present on the
> >2.4GHz band. And any 802.11b AP or 802.11b client will not be able to
> >"see" the 802.11g AP or 802.11g clients or the 802.11g traffic. So the
> >end result will be slow traffic on the 802.11g AP.
> >
> >Better would be using an 802.11a AP, which uses the 5GHZ band and does
> >not interfer with 2.4GHz traffic for your fast connection.
>
> Usually easier and cheaper to use a minimally-overlapping 2.4 GHz
> channel.

Not in this case. See fig 12-7 "Channel separation in 802.11 DS
networks" on page 259 in "802.11 Wireless Networks" 2nd ed, by Matthew S
Gast. There's overlap using channels 1 and 11.

John Navas <(E-Mail Removed)> wrote:

> On Thu, 9 Jul 2009 02:33:48 +0200, (E-Mail Removed) (Axel
> Hammerschmidt) wrote in <1j2kenr.1uovelx6ifodeN%(E-Mail Removed)>:
>
> >John Navas <(E-Mail Removed)> wrote:
>
> >> Usually easier and cheaper to use a minimally-overlapping 2.4 GHz
> >> channel.
> >
> >Not in this case. See fig 12-7 "Channel separation in 802.11 DS
> >networks" on page 259 in "802.11 Wireless Networks" 2nd ed, by Matthew S
> >Gast. There's overlap using channels 1 and 11.
>
> Not significant.

<snip>

Wrong figure.

<http://tinyurl.com/n4avys>

This should bring you to fig 12-5. There you will see, that the spread
is greater than 22 MHz. Scroll down to fig 12-7. Although weak, when the
802.11b and 802.11g APs are close to each other, as will be the case
here, there will be interference.

Steve Fenwick:

<snip>

> If an AP is set for 802.11g only, it will ignore 802.11b traffic as
> noise. It won't do CTS/RTS with it, which is part of what appears to
> slow down the 11g traffic.

<http://tinyurl.com/nby8mw>

Scroll back up to Protection.

> 5GHz does not penetrate walls and other obstacles as well as 2.4GHz.

Not so. In theory, 802.11b/g will have marginaly longer range.


--
Oops!... I did it again

John Navas <(E-Mail Removed)> wrote:

<snip>

> From your source:
>
> 802.11b specifies that a 25 MHz (5 channel number) spacing is
> sufficient. Figure 12-7 shows the spectral mask of transmission on
> the so-called non-overlapping channels (1, 6, 11).
>
> Figure 12-7 shows the amount of overlap and interference between
> channels 1 and 11 to be not significant.

From your posting:

Message-ID: <(E-Mail Removed)>

"Put them on different minimally overlapping channels (1, 6, 11)."

And:

Message-ID: <(E-Mail Removed)>

"... a minimally-overlapping 2.4 GHz channel."

The Navas Group, a rock 'n' roll band?

Steve Fenwick <(E-Mail Removed)> wrote:

> In article <Xns9C43B1ADCDE1Chlexahotmailcom@130.133.1.4>,
> Axel Hammerschmidt <(E-Mail Removed)> wrote:
>
> > Steve Fenwick:
> >
> > <snip>
> >
> > > If an AP is set for 802.11g only, it will ignore 802.11b traffic as
> > > noise. It won't do CTS/RTS with it, which is part of what appears to
> > > slow down the 11g traffic.
> >
> > <http://tinyurl.com/nby8mw>
> >
> > Scroll back up to Protection.
>
> Which is what I said--put the AP in 802.11g radio only, and protection
> will not be enabled.

Read it again. Take note of:

: One of the major differences between 802.11b and 802.11g is
: protection, which is reguired...
:
: [...]
:
: Protection is activated whenever there is a need to ensure 802.11g
: stations do not interfere with 802.11b stations.
:
: [...]
:
: Protection is activated when a non-802.11g station associates with the
: network, as well as when non-802.11g-capable stations are transmitting
: in the area.
:
: [...]
:
: By shunning stations that are not capable of 802.11g speeds, there is
: an increased probability that protection can remain disabled. Of
: course, a station that is shunned may very well find a different
: network that can accomodate it on the same channel, which would still
: trigger the activation of protection.

When you put the AP in 802.11g mode and turn off Protection, it will run
in 802.11g mode without protection until the first 802.11b station in
the area starts transmitting. Even when this 802.11b station ends up
associating some another AP on a different channel, the station will
have scanned all available channels and triggered the activation of
protection on the 802.11g-only AP, halving throughput.

And when the AP has a "manuel switch" for activating protection,
protection will stay on until the AP is rebooted (or the Protection
"switch" in the AP setup is "toggled"). Otherwise, there would be no
reason for having the Protection switch in the first place.

> > > 5GHz does not penetrate walls and other obstacles as well as 2.4GHz.
> >
> > Not so. In theory, 802.11b/g will have marginaly longer range.
>
> Which is what I said--2.4GHz (the band used for 802.11b/g) has better
> range (and wall penetration) than 5GHz.

You speculate. How many 802.11b/802.11g APs have you actually compared?

Steve Fenwick <(E-Mail Removed)> wrote:

> In article <1j2p1jp.1hqetzbjacsweN%(E-Mail Removed)>,
> (E-Mail Removed) (Axel Hammerschmidt) wrote:
>
> > Steve Fenwick <(E-Mail Removed)> wrote:

<snip>

> > > Which is what I said--2.4GHz (the band used for 802.11b/g) has better
> > > range (and wall penetration) than 5GHz.
> >
> > You speculate. How many 802.11b/802.11g APs have you actually compared?
>
> Quite a few--it's part of my work. How many have you tested?

Hmm! An 802.11 professional, unfamiliar with 802.11g 802.11b protection.

You've published your comparisons where?

Jeff Liebermann <(E-Mail Removed)> wrote:

<mega-snip: all beside the point>

> >And when the AP has a "manuel switch" for activating protection,
> >protection will stay on until the AP is rebooted (or the Protection
> >"switch" in the AP setup is "toggled"). Otherwise, there would be no
> >reason for having the Protection switch in the first place.
>
> I don't know any AP's that have such a hardware switch.

Where does it say "hardware"?

> I'll assume you mean a software or configuration switch. In all routers
> that I've seen, the choices are roughly:
> 802.11b only
> 802.11g only
> 802.11b+g mixed.
> Is this the switch or did I miss something between the lines?

<http://users.cybercity.dk/~dsl487543/Protection.png>

Trendnet TEW-510APB, 802.11a/b/g, with B/G mode usualy turned off.

Jeff Liebermann <(E-Mail Removed)> wrote:

> On Mon, 13 Jul 2009 18:01:44 +0200, (E-Mail Removed) (Axel
> Hammerschmidt) wrote:

<snip>

> ><http://users.cybercity.dk/~dsl487543/Protection.png>
> >
> >Trendnet TEW-510APB, 802.11a/b/g, with B/G mode usualy turned off.
>
> Perhaps I'm a bit dense this morning, but I don't see anything on that
> page that looks like an 802.11b protection on/off switch. The only
> item which seems involved is "Allow 54Mbs Stations Only" which seems
> rather vague. Does it turn off 5.7GHz? Does it disable speeds above
> 54Mbits/sec? Does it lock the router to 54Mbits/sec as the only
> speed? Got a clue what it means? It's kinda academic as you have it
> disabled.

What's your question got to do with 802.11g 802.11b protection?

> So, where is the disable 802.11b compatibility mode "manual switch"
> you previously mentioned? Did I miss something (possibly on a
> different web page)?

The switch on the fourth-, third- and second bottom line turn off
802.11g 802.11b protection, until 802.11b traffic is detected. Depending
on how the switch on fifth bottom line is set. The choice is between
different methods.

Below is another example, from the (CD-) manual for my ASUS WL-330gE
multi-function pocket router:

"Wireless Mode

This field indicates the 802.11g interface mode. Selecting "Auto" allows
802.11g and 802.11b clients to connect to the ASUS 802.11g AP. Selecting
"54g Only" maximizes performance, but prevents 802.11b clients from
connecting to the ASUS 802.11g AP. If "54g Protection" is checked, GMode
protection of 11g traffic is enabled automatically in the presence of
11b traffic."

As I read the last part, considering that 802.11b protection on 802.1g
devices is required - see earlier posts, it means that "54g Protection"
will be on all the time when not checked.

Can't you read AYBABTU?

Here's another one, from my routers firewall.

"If checked, the undefined item in IP Address list is allowed to access
Internet;Unchecked means reverse."

Jeff Liebermann <(E-Mail Removed)> wrote:

> On Mon, 13 Jul 2009 20:24:31 +0200, (E-Mail Removed) (Axel
> Hammerschmidt) wrote:

<snip>

> >The switch on the fourth-, third- and second bottom line turn off
> >802.11g 802.11b protection, until 802.11b traffic is detected. Depending
> >on how the switch on fifth bottom line is set. The choice is between
> >different methods.
>
> I don't think so. Most of that is CTS/RTS "protection", not 802.11b
> protection. It protects against collisions caused by hidden nodes
> (where multiple clients can't hear each other and therefore tend to
> transmit simultaneously). At least that's what I think it means.

I'm afraid you're wrong.

Hidden node protection is set by twiddling the RTS/CTS Threshold knob.
You'll notice there are two such knobs on the screenshot, one for when
the radio is on the 5GHz band - the top pane - and one for when the
radio is on the 2.4GHz band. There's only the one radio in this model
AP. And you don't see the 802.11b protection switches in the top pane,
because it's not needed for the 5GHz band.

Not all 802.11g AP's have 802.11b protection switches. My D-Link
DWL-G700AP and DWL-G730 pocket router do not, f.ex. It's an ekstra
feature. However, they do have an RTS/CTS Threshold knobs.