Re: 3com WAP - public/secure and 'N' vs B/G


"LR" <lrme@xxxxxxxxxxx> wrote in message
news:OdadnR9eZ_NUtCjUnZ2dnUVZ8q-WnZ2d@xxxxxxxxx
On 05/03/2009 16:45, LR wrote:
On 05/03/2009 15:33, ps56k wrote:
"LR"<lrme@xxxxxxxxxxx> wrote in message
news:pZedndyweZrdCjLUnZ2dnUVZ8o-WnZ2d@xxxxxxxxx
On 05/03/2009 03:23, ps56k wrote:
I was at our local library today,
and it appears they have several WAP's installed,
but I had problems getting connected...

There are two SSID's -
one is public and one is private/secure.

Using WiFi Hopper it displayed a couple of 3Com access points
with what appeared to be "related" MAC addresses...
00:22:57:00:13:40 - public
00:22:57:00:13:42 - secure

Anyway - when I got home& sent an email to their "tech" person
and mentioned that I was having a problem,
here was the jist of the reply...
Wrong tech language makes me not hopeful :)

Since I don't have anything running B/G/N -
could they have something configured to support N,
that accidently doesn't allow B/G to connect - and they don't know
it :)
If they are running an 802.11n network they don't have to allow 11b
or 11g
to connect, the draft 11n only says that the equipment must be
capable of
connecting to legacy devices so the user can have the capability to
run a
mixed network.
Look at the set of 11n mode options that are available on this emulator
<http://support.dlink.com/Emulators/dir655/Basic_Wireless.html>

If the access point is setup for 802.11n - and only 802.11n -
would I still see the SSID beacon on my b/g card via NetStumbler,
Hopper,
Windows ?

Is the beacon packet seen by all technologies at the lowest common
"speed&
structure",
and only goes into 802.11n mode after the actual connection ?

Would I see the SSID, but just not be able to establish a connection ?


Without actually trying it I am not sure exactly what you would get.
I have been doing a bit of reading about N recently and am not sure how
some of these "legacy" connections are supposed to work.
"During the definition of the 802.11g standard, it was realized that,
since legacy 802.11b devices would not be able to decode the newer
802.11g frames, there ought to be a separate mechanism to help legacy
devices set their NAV correctly and therefore to reduce the percentage
of collisions on air. The 11g standard made use of existing ?protection
mechanisms? ? RTS and CTS ? to help legacy stations set their NAV.
A similar situation arose during the definition of the 802.11n standard.
Legacy 802.11a/b/g devices would not be able to decode the 802.11n
headers ? and therefore a protection mechanism becomes necessary. One of
these is the transmission of legacy preamble and header that enable the
802.11a/g/ device to detect the 802.11n packet and to decode the
information in its signal field, from which the correct packet duration
can be determined."
<http://www.redpinesignals.com/Wireless-Handheld-Devices-The-802-11n-Advantage.pdf>


My reading of that is you should see something.

There was also this
"Backward compatibility with legacy devices also may be enabled by
forcing devices that are compliant with a newer version of the standard
to transmit special frames using modes or data rates that are employed
by legacy devices. For example, the newer devices may transmit Clear to
Send/Ready to Send exchange frames or Clear to Send to self frames as
may be employed in standard 11g. These special frames contain
information that sets the network allocation vector of legacy devices
such that these devices know when the wireless channel is in use by
newer stations."
<http://www.faqs.org/patents/app/20090028106>

I have heard mixed reports about even using an 11n card with netstumbler
with some people not getting it to work and one person who got it work
only having it report speed at 54Mbs.


Having got my XP laptop put back together and eventually finding someone
who has an 11N only network I ran a few programs. I have used only b/g
wireless cards.
Kismet in Ubuntu reports an 802.11n network.
XPSP2 laptop running the following:-
1.WZC reports the SSID.
2.Wifihopper reports SSID and an 11g network with the selected "40MHz"
channel.
The graph function works as well.
3.Inssider reports SSID but the graph function doesn't work.
4.Netstumbler was erratic to say the least. It wouldn't reliably report
the SSID although it did report the correct MAC address. The graph would
not work, you got a single line at the start and that was that.
I later found that if the 11n "standard channel", assumption on my part,
coincided with the channel that one of the nearby AP's was using then the
graph stopped however if that AP was then switched off the graph would
resume, it was pure luck that that AP was switched off.

Vista SP1:-
1.Vista "connect to a network" shows the SSID.
2.Vistumbler 8.1 showed SSID and that it was an 11n network and the
"40MHz" channel.
3.Inssider showed SSID and the "40MHz" channel. The graph function worked
in Vista.
4.Xirrus WiFi Inspector showed SSID and that it was an 11n network. It
also showed 2 channels,"wide" and "standard" I assume, which is why I went
back and checked Netstumbler again and found the graph was now working and
one of the AP's was no longer transmitting.
5.None of the versions of wifihopper work correctly with the atheros b/g
card in my Vista laptop. The latest version 1.2 build 2008-110600 reports
all networks as type 11a, so it works after a fashion but didn't try it as
there may be other bugs.
5.Inssider and Vistumbler are based on "netsh" commands so I didn't try
that either.

None showed speeds greater than 54Mbs.

I have assumed that the 2 channels picked up by the Xirrus wifi inspector
is correct and not a fault with the 11n AP or the Xirrus tool. The second
channel I have assumed to be the "standard channel" and this does cause a
problem for netstumbler if another AP is using it as well. I would be
interested to know if anyone else has used this tool and noticed whether
they have picked up 2 channels with an 11n network.

since you could see the SSID -
what happens when you try to connect to the 802.11n-only network ?

and how did Hopper display the 802.11n with the 40mhz channel ?
that would be my giveaway for a N-only network.



.

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