Overcoming wireless networking interference problems

Can anyone point me to information on how to diagnose and overcome
interference problems in WiFi networks, please?

Most of the advice I've seen so far is fairly superficial (different
channel, move access point, waggle aerials etc) and has been
ineffective IME.

That is good advice. The only other thing to suggest is what about 2.4GHz
cordless phones or a microwave.

Jeff


"Frank le Spikkin" <(E-Mail Removed)> wrote in message
news:Xns956ECE46117FlSxxx@130.133.1.4...
> Can anyone point me to information on how to diagnose and overcome
> interference problems in WiFi networks, please?
>
> Most of the advice I've seen so far is fairly superficial (different
> channel, move access point, waggle aerials etc) and has been
> ineffective IME.
>

"Jeff Durham" <(E-Mail Removed)> wrote in message
news:WlK4d.106739$(E-Mail Removed)...
> That is good advice. The only other thing to suggest is what about 2.4GHz
> cordless phones or a microwave.
>
> Jeff
>
>
> "Frank le Spikkin" <(E-Mail Removed)> wrote in message
> news:Xns956ECE46117FlSxxx@130.133.1.4...
>> Can anyone point me to information on how to diagnose and overcome
>> interference problems in WiFi networks, please?
>>
>> Most of the advice I've seen so far is fairly superficial (different
>> channel, move access point, waggle aerials etc) and has been
>> ineffective IME.
>>
>
>
Have you used something like Network Stumbler to look for what networks
already exist in your area? Do this with your AP turned off. There might
be several networks in your area, on different channels, that are
interfering.

When setting up a wireless network for the marina where I keep my boat, I
found at least 5 other APs that broadcasted ocasionally. And one seemed to
knock me off my network any time it popped its ugly head up. goo that it
was rarely present.

You might also advise what is the problem you are trying to solve? You say
"interference" but is the real issue that you cannot communicate with your
AP? The root cause might be a range or obstacle issue.

--
Bob Alston

bobalston9 AT aol DOT com


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"Bob Alston" <(E-Mail Removed)> wrote in
news:RsK4d.289234$Lj.95971@fed1read03:

>
> "Jeff Durham" <(E-Mail Removed)> wrote in
> message news:WlK4d.106739$(E-Mail Removed)...
>> That is good advice. The only other thing to suggest is what
>> about 2.4GHz cordless phones or a microwave.
>>
>> Jeff
>>
>>
>> "Frank le Spikkin" <(E-Mail Removed)> wrote in message
>> news:Xns956ECE46117FlSxxx@130.133.1.4...
>>> Can anyone point me to information on how to diagnose and
>>> overcome interference problems in WiFi networks, please?
>>>
>>> Most of the advice I've seen so far is fairly superficial
>>> (different channel, move access point, waggle aerials etc) and
>>> has been ineffective IME.
>>>
>>
>>
> Have you used something like Network Stumbler to look for what
> networks already exist in your area? Do this with your AP
> turned off. There might be several networks in your area, on
> different channels, that are interfering.
>
> When setting up a wireless network for the marina where I keep
> my boat, I found at least 5 other APs that broadcasted
> ocasionally. And one seemed to knock me off my network any time
> it popped its ugly head up. goo that it was rarely present.
>
> You might also advise what is the problem you are trying to
> solve? You say "interference" but is the real issue that you
> cannot communicate with your AP? The root cause might be a
> range or obstacle issue.
>
Thanks for the replies Jeff and Bob.

The particular case I experienced this week:
- AP (Netgear DG834G wireless ADSL router) and adapter work fine in
my workshop, rock solid signal, no dropouts in continuous ping
testing and Netstumbler graph.
- At the target premises (small shop in crowded village High
Street), initially appeared to work, some dropouts but acceptable
performance. Strong signal shown on Netstumbler, low noise,
until...
- blattttt, connection lost no signal visible with Netstumbler.
Intermittent reconnection, totally unacceptable performance.
- Netstumbler shows no signal, no access point at all.
- Tried all the tricks, 11b only, 11g only, different channels,
moved the router etc to no avail.
- Interference disappears periodically, but only for a few minutes
at a time.
- Same results on two visits to the site. After several hours of
trying, reverted to a wired configuration.

So the interferer is unidentifiable using the tools to hand, and
I'm helpless to do anything about it - hence my OP question.

Perhaps this is a hardware problem. Can you take it back to the pristine
location and see if everything works? I did have an access point actually
die on me a few weeks ago. It would work for an hour or two and then just
quit responding. When accessing it through its IP address, I could page
through the configuration pages, but then it would slow down, and then quit
responding. That was done through a wired connection.

Jeff


"Frank le Spikkin" <(E-Mail Removed)> wrote in message
news:Xns956E560C74DD7FlSxxx@130.133.1.4...
> "Bob Alston" <(E-Mail Removed)> wrote in
> news:RsK4d.289234$Lj.95971@fed1read03:
>
>>
>> "Jeff Durham" <(E-Mail Removed)> wrote in
>> message news:WlK4d.106739$(E-Mail Removed)...
>>> That is good advice. The only other thing to suggest is what
>>> about 2.4GHz cordless phones or a microwave.
>>>
>>> Jeff
>>>
>>>
>>> "Frank le Spikkin" <(E-Mail Removed)> wrote in message
>>> news:Xns956ECE46117FlSxxx@130.133.1.4...
>>>> Can anyone point me to information on how to diagnose and
>>>> overcome interference problems in WiFi networks, please?
>>>>
>>>> Most of the advice I've seen so far is fairly superficial
>>>> (different channel, move access point, waggle aerials etc) and
>>>> has been ineffective IME.
>>>>
>>>
>>>
>> Have you used something like Network Stumbler to look for what
>> networks already exist in your area? Do this with your AP
>> turned off. There might be several networks in your area, on
>> different channels, that are interfering.
>>
>> When setting up a wireless network for the marina where I keep
>> my boat, I found at least 5 other APs that broadcasted
>> ocasionally. And one seemed to knock me off my network any time
>> it popped its ugly head up. goo that it was rarely present.
>>
>> You might also advise what is the problem you are trying to
>> solve? You say "interference" but is the real issue that you
>> cannot communicate with your AP? The root cause might be a
>> range or obstacle issue.
>>
> Thanks for the replies Jeff and Bob.
>
> The particular case I experienced this week:
> - AP (Netgear DG834G wireless ADSL router) and adapter work fine in
> my workshop, rock solid signal, no dropouts in continuous ping
> testing and Netstumbler graph.
> - At the target premises (small shop in crowded village High
> Street), initially appeared to work, some dropouts but acceptable
> performance. Strong signal shown on Netstumbler, low noise,
> until...
> - blattttt, connection lost no signal visible with Netstumbler.
> Intermittent reconnection, totally unacceptable performance.
> - Netstumbler shows no signal, no access point at all.
> - Tried all the tricks, 11b only, 11g only, different channels,
> moved the router etc to no avail.
> - Interference disappears periodically, but only for a few minutes
> at a time.
> - Same results on two visits to the site. After several hours of
> trying, reverted to a wired configuration.
>
> So the interferer is unidentifiable using the tools to hand, and
> I'm helpless to do anything about it - hence my OP question.
>

Jeff Durham <(E-Mail Removed)> wrote:
> That is good advice. The only other thing to suggest is what about 2.4GHz
> cordless phones or a microwave.

I don't see any interference in NetStumbler with two different microwave
ovens on an Orinoco or DLink DWL-122. I suppose some ovens might leak, but when
they first came out, I was working in radar that used a magnetron at the
same frequency. We didn't "see" microwave ovens.:w

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

On 24 Sep 2004 07:27:31 GMT, Frank le Spikkin <(E-Mail Removed)> wrote:

>The particular case I experienced this week:
>- AP (Netgear DG834G wireless ADSL router) and adapter work fine in
>my workshop, rock solid signal, no dropouts in continuous ping
>testing and Netstumbler graph.

Ping for testing a system isn't really that good. You need to move
large amounts of data for testing. Try one of the numerous online
speed tests and run some streaming media to be sure that everything is
working as expected.

>- At the target premises (small shop in crowded village High
>Street), initially appeared to work, some dropouts but acceptable
>performance. Strong signal shown on Netstumbler, low noise,
>until...

How long is initially? Minutes, hours, days? If it's interference,
duz it go away at night, or on weekends?

>- blattttt, connection lost no signal visible with Netstumbler.
>Intermittent reconnection, totally unacceptable performance.
>- Netstumbler shows no signal, no access point at all.

It might be interference. Judging by the general description it
sounds like you might be near a cafeteria or establishment that runs
microwave ovens almost continuously. We had a local market that
effectively ran their sandwitch shop microwave oven erratically all
day long. When it ran, wireless within about 1000ft radius was
futile. I had to borrow a spectrum analyzer to verify. Eventually, I
convinced them to clean the encrusted food off the door seal and life
returned to normal.

I don't think it's a cordless phone. The non-spread spectrum phones
I've watched tend to occupy the bottom channels. They start at the
low frequency edge and dribble up in frequency until they find a clear
channel. The spread spectrum ones are really evil. They use
frequency hopping (FHSS) instead of direct sequence (DSSS). FHSS is
required to hop over the entire band (75 out of 79 channels) before
re-using a channel. It clobbers everything. However, they are also
very low power and are used intermittantly (unless you have
teenagers). No way would one cause a dropout or disconnect unless the
phone were literally next to the radio or access point.
http://www.wi-fiplanet.com/tutorials...le.php/2191241

Another possibility are the new and disgusting metropolitan lans.
This is where the local municipality installs high power store and
forward repeaters on street lights to build a mesh network. Every
mesh network I've seen eventually ends up spewing continuous packets
in its never ending effort to inefficiently send duplicate packets to
the entire network. The problem with these isn't just the excessive
traffic, it's the tendency to use over powered radios for the intended
purpose. Most are running full power (4 watts EIRP) and are fully
capable of clobbering any local traffic. The better units use
multiple radios and channels for store-n-forward, so channel shifting
may not be effective. See:
http://www.tropos.com

A variation on the theme are high powered central access points with
highly directional and steerable antennas. The FCC considers these to
be "point to point" instead of "point to multipoint" and therefore
allows them to use additional power. If you happen to be badly
located, these can be a major source of interference.
http://www.vivato.net

>- Tried all the tricks, 11b only, 11g only, different channels,
>moved the router etc to no avail.
>- Interference disappears periodically, but only for a few minutes
>at a time.
>- Same results on two visits to the site. After several hours of
>trying, reverted to a wired configuration.
>
>So the interferer is unidentifiable using the tools to hand, and
>I'm helpless to do anything about it - hence my OP question.

Did you run this test with the client radio fairly close (a few feet)
from the access point, or is there some distance (or a wall) between
the two? If you're getting dropouts while next to the access point,
the interference must either be massive, or the radio(s) defective.

Try a different client radio. Try removing the antenna from the
access point temporarily to reduce anything it might pickup from a
nearby source of interference. If the problem goes away, it's most
surely something that's being picked up by the access point receiver,
and therefore is interference. However, if the problem persists,
there's something broke with the radios.

If none of this does any good, try to borrow a spectrum analyzer and a
directional dish or patch antenna. You're at a disadvantage with a
spectrum analyzer as you lose the benifits of SS processing gain.
With the signal spread over 26MHz (DSSS) or 80Mhz (FHSS or channel
bonded DSSS), it's difficult to see unless you're close. The gain of
the antenna will help. I built a receive pre-amplifier in the dish
antenna feed in order to improve sensitivity (and largely eliminate
coax cable losses).

If you can find or afford to borrow a real spectrum analyzer, a
tolerable substitute is a FHSS receiver with appropriate software.
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=5722353685
(Does NOT work with Windoze XP). Sensitivity is tolerable, but it has
the adantage of being portable. If the interference is sufficiently
bad to cause a disconnect, it should be easily visible.

My guess(tm) is:
1. microwave oven or industrial platic molding pre-heater.
2. defective access point or client radio.
3. Metropolitan LAN or mesh network interference.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

On Fri, 24 Sep 2004 16:03:05 +0000 (UTC),
(E-Mail Removed) wrote:

>Jeff Durham <(E-Mail Removed)> wrote:
>> That is good advice. The only other thing to suggest is what about 2.4GHz
>> cordless phones or a microwave.

>I don't see any interference in NetStumbler with two different microwave
>ovens on an Orinoco or DLink DWL-122. I suppose some ovens might leak, but when
>they first came out, I was working in radar that used a magnetron at the
>same frequency. We didn't "see" microwave ovens.:w

You didn't look hard enough. Leaky microwave ovens are quite obvious.
Here are some sample photos from the Tektronix catalog:
http://www.tek.com/Measurement/cgi-b.../catalog/3026/

There are also hams that have too much time on their hands:
http://lea.hamradio.si/~s57uuu/mischam/magnetr/

Netstumbler works by "active probing" the access point for it's SSID
with a probe request frame (with a broadcast BSSID and a blank SSID),
that is answered by an access point or ad-hoc client with a probe
response frame. Netstumbler won't "see" anything that does't respond.
Neither will any of the 802.11a/b/g sniffers (Wellenreiter).


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

Jeff Liebermann <(E-Mail Removed)> wrote:
> Ping for testing a system isn't really that good. You need to move
> large amounts of data for testing.

What about a long ping packet?
from unix
ping -c 5 -s 1000 host
from windows-cmd
ping -n 5 -l 1000 host

A better tester might be iperf, if you have access to a windows or unix
machine you can use as the host & client at the other end.
This allows long tests. It seems to get funky after 10 minutes, but a
minute is probably sufficient.
Start a server
iperf -s
from the other machine
iperf -c the_host_ip
runs a 10 second test. Reverse host and client roles, or invoke other
iperf options to test the other way. You might need to open a firewall
port 5100 to reverse the roles and make your wireless the server.
< http://dast.nlanr.net/Projects/Iperf/ >

Streaming audio or video pauses and dropouts are obvious indicators of a
network glitch. Unfortunately, those happen on my wired connections, so
they indicate "trouble" under normal traffic conditions.

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

As viewed from alt.internet.wireless, Jeff Liebermann wrote:

>We had a local market that effectively ran their sandwitch shop
>microwave oven erratically all day long. When it ran, wireless
>within about 1000ft radius was futile. I had to borrow a spectrum
>analyzer to verify. Eventually, I convinced them to clean the
>encrusted food off the door seal

Yecch. If word of that encrustation had gotten out, their sandwich
business might have dropped off to the point where the now-occasional
interference might not have been a problem any longer...

>and life returned to normal.

Except for the employees who had been operating the microwave.
After getting nuked on a long-term basis, some of their kids might
be born with two heads...

--
Jafo