Philip Herlihy <thiswillbounceback@you.com> hath wroth:
>I thought I was onto something when I bought WirelessMon, which showed
>about 8 wireless networks, all only intermittently available except for
>the Thomson ST180 (about -45dB).
WirelessMon:
<http://www.passmark.com/products/wirelessmonitor.htm>
will not show 2.4GHz devices that cannot be received by your laptop or
whatever you're using to run WirelessMon. For example, if somone
setup an access point nearby running some MIMO mutation, with all the
compatibility options turned off, you won't see it. Same with
108Mbits/sec only access points. So see those, you need spectrum
analyzer.
>The Netgear WG602v3 is much stronger
>upstairs (that's where it lives) at about -15dB, but WirelessMon shows
>it coming and going several times a minute, seen through the wireless
>card of one machine which manages a steady connection to the ST180 two
>floors below.
Ok, not stop and think. What would cause the signal to come and go
like that? Is there an other access point around on the same SSID?
Any possible sources of intereference? The last time I saw something
like that, the office had a mess of 2.4GHz wireless cameras (non-WiFi)
that everyone conveniniently was ignoring. Start turning things off
until you get a steady signal. If you can't do that, take the WG602v3
into a basement or isolated location, and see if you can get a steady
signal there.
>Another nearby machine can't get a steady hold on the
>downstairs WAP, and can't bind to the upstairs one.
Ok, you have 3 floors, none of which will pass RF through the floors.
My guess for an office building are poured concrete floors, which have
that characteristic. The only way this is going to work is one access
point per floor. Forget about going through the floors.
>I replaced the Netgear WG602v3 with a US Robotics USR5416. No
>improvement: the signal in WirelessMon was still shown as coming and
>going while the downstairs ST180 was steady as a rock.
Ok, that eliminates the access point as the culprit. What else is
belching 2.4Ghz in the area? Note that this includes 2.4GHz desktops
and such. See list at:
<http://wireless.wikia.com/wiki/Wi-Fi#Interference>
for probable culprits.
>Changing channel on the downstairs ST180 allowed one PC to get a
>connection but another one lost it, so I changed back, restoring the
>previous situation.
Hmmm... what floor numbers are you on? If you're very high above the
ground, with a good view of the city, you're going to pickup plenty of
interference. It may not be particularly strong, but it's going to be
from many different sources. Your screenprint of the WirelessMon
output shows a huge number of other systems, any one of which can
cause interference. I suggest that you:
1. Install a low gain, but directional antenna that keeps the RF
pattern inside the building. Something about 8dBi gain with at least
a 90 degree beamwidth (AMOS or Franklin Antenna).
2. Move the access points away from the windows with a view. If
difficult, put a piece of sheet metal or aluminium foil behind the
antenna in the direction of the outside windows.
3. Select a channel number (1, 6, or 11) with the fewest *NUMBER* of
other systems.
>I disabled the PCI card on the "unlucky" PC upstairs and fitted a US
>Robotics USR5420 adapter, which was able to bind to the weak signal from
>downstairs, but not the Netgear WG602v3 upstairs. Substituting the
>USR5416 again (configured so that it's possible just to switch the
>boxes) produced a loss of ability to bind to the ground floor in the PC
>with the USR5420 USB adapter, and it couldn't bind to the USR5416.
No clue what the signal strength and noise level are doing during
these changes. Are you recording numbers as you go along? If not,
how will you know you're making an improvement? Juggling adapters
(assuming they're not defective) will not have anywhere as big an
effect as better antennas. With desktop PCI, the problem is that the
supplied antennas are too small, buried behind the PC, on the floor,
and in the middle of a mess of cables. In other words, the worst
possible location. If you insist on PCI, then get an external
antenna. If you insist on shooting through concrete floors, get a
*BIG* external antenna with lots of directional gain.
>Today I've tried fiddling with the various settings on the (reinstated)
>Netgear WG602v3. While the downstairs ST180 remains on WEP (128), I
>switched the WG602v3 to WPA-PSK. No improvement. I've also tried
>reducing the data rate from "Best" to 24Mb/s, and changed from "g or b"
>to "g only". No improvement.
Have you tried checking to see at what speed your various clients are
connecting to the access points? This is usually a good indication of
signal "quality". The lower the speed, the more flakey the
connection. Do this after passing some traffic as many clients
increase their speed back to 54Mbits/sec when the traffic stops. If
you're down to 11Mbits/sec or less, you don't have have a good path,
enough signal, or are infested with an interference (noise) problem.
>Meanwhile, a network in their other office with a single Thomson ST180
>and 8 of the same PCI cards soldiers on without a blink. If I could get
> another ST180 I would!
Continues on at what speed? If your DSL connection is running at
perhaps 1.5Mbits/sec, you could be connected at 5.5Mbit/sec and never
really notice the slow connections. Numbers, not prose, please.
>So, the only thing I can think of is to start replacing the wireless PCI
>cards, inclining towards US Robotics.
I used to have a slogan for such ocassions, where no obvious solution
was avaialable. "Change Everything". I even was given a rubber stamp
with that inscribed. I think you'll find that doing a "site survey"
with WirelessMon or Netstumbler will show that you have crappy signal
between floors and lots of interference near windows if you're high
up.
I also take issue to using PCI wireless cards in an office
environment. The money you save in not having to do wiring is lost in
such troubleshooting exercises. You also won't get anywhere near the
speed and reliability of a wired network. PC's that do not move
should use wired ethernet connections. They should also not try to
shoot through floors. The only place I've seen wireless desktops used
effectively was on crash carts in a hospital and a laboratory. The
others ended up wired. Leave the wireless for the laptops and PDA's
which can pick their location for best signal.
>However, if you've been generous
>enough to read this far and can suggest ANYTHING else worth trying, I'll
>be greatly indebted to you.
Numbers.... give me numbers and I can deduce the problem.
Signal strength, variations in signal strength, noise level,
variations in noise level, connection speed, variation in connection
speed, and results of performance tests.
For a performance test, use IPerf with a wired desktop acting as a
temporary server. For destructions, see my rant at:
<http://groups.google.com/group/alt.internet.wireless/msg/c3b86f0702ee496c>
Notice that I really don't care what speed you get from the internet.
It's the local wireless speeds that are important. Therefore, don't
bother with an internet based speed test.
>PS: I've stumbled on NetStumbler, which is useful. Here's a screnshot:
>http://homepages.rya-online.net/pher...Screenshot.gif
>26 networks detected after an hour's running (up to 40 36 hours later!).
Propagation and moving reflections will produce additional systems.
Those that do not broadcast their SSID will not be shown. Just
eliminate those that have very few beacons heard.
It's also not very nice running continuous probe requests for several
days. My IDS system treats that as an active attack in progress and
will block any ICMP packets to your MAC address. Run it for perhaps
30 minutes and you'll see all of the strong signal systems.
I also see another possible problem. I don't think that "/" and "#"
are valid characters for the SSID. It's suppose to be only
alphanumeric characters. Many AP's will accept other characters, but
I've seen some clients choke on these.
> I've sorted by max SNR (Signal to Noise Ratio) although I'm not
>certain the "noise" part of that value is being correctly reported.
>Coincides with max Signal, though.
Actually, the noise values are very important. They usually sit at a
fairly low value. However, if they increase above some base value,
that means that there was interference present when the probe packets
were received.
>Just one signal stays steady as a rock, and it isn't the strongest!
For the time being, I suggest you ignore interference and concentrate
on signal quality and strengths to your own access points. My
guess(tm) is that you don't have enough signal through the floors and
that even the slightest interference will cause packet loss or
disconnects. The IPerf thruput tests should demonstrate that clearly.
--
Jeff Liebermann
jeffl@cruzio.com
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Always one PC dropping out intermittently no matter what I try.... 
Linear Mode
