Wireless network problem

Hello all,

I am having an issue with a warehouse management implementation. Here
is the scenario. We have 4 Symbol ap4131 access points in our
warehouse, and 18 PDT6800 handheld scanners. We have 2 of the AP's set
at channel 1, and the other 2 at channel 11. This was recommended by
Symbol to try and eliminate interference between the AP's. I also have
2 linksys 802.11G aps in the warehouse both at channel 8 , with hawking
Hi-gain antennas.

The issue we are having is the PDT6800's are constantly dropping
(randomly throughout the day), and unable to reconnect for just about
exactly the same amount of time every single time it happens (just about
10 minutes). We have changed the type of handheld radios we used, as
well as turned off all the other access points (besides the symbols.).
I had asked about the 3Com card earlier this week in this group in hopes
of someone helping me find a wireless nic for a laptop that can use
promiscuous mode. I was also hoping someone might be familiar with a
situation such as this, and make some recommendations as to how I would
attack it. Truthfully I am at a loss at the moment. I did happen to
have my laptop connected to one AP when the PDT6800 lost connection,
but there was nothing there to lead me to believe that this would
happen, and really I have no idea which direction to go from here.

It happens mostly to the AP's and PDT6800's in the back of the
warehouse, where I have 2 aps within about 50' of each other, yet on
different channels.

I apologize for being so vague, if there are any specific questions that
will help you guys diagnose this situation please do not hesitate to
ask, and I will do my best to relay the information to you.

thanks again,

Chris

On Sun, 09 Oct 2005 22:30:10 GMT, Chris Rennert <crennert@new.rr.com>
wrote:

>I am having an issue with a warehouse management implementation. Here
>is the scenario. We have 4 Symbol ap4131 access points in our
>warehouse, and 18 PDT6800 handheld scanners. We have 2 of the AP's set
>at channel 1, and the other 2 at channel 11. This was recommended by
>Symbol to try and eliminate interference between the AP's. I also have
>2 linksys 802.11G aps in the warehouse both at channel 8 , with hawking
>Hi-gain antennas.

The non-overlapping channels are 1, 6, and 11. The radios on channel
8 and 11 will somewhat interefere with each other. I would move the
Linksys access points from 8 to 6.

>The issue we are having is the PDT6800's are constantly dropping
>(randomly throughout the day), and unable to reconnect for just about
>exactly the same amount of time every single time it happens (just about
>10 minutes).

Look for microwave oven, 2.4GHz cordless phones, wireless security
cameras, 2.4Ghz wireless mouse, Bluetooth phone base near the access
points, microwave plastic pre-heater, 2.4Ghz sulphur lamp, Zigbee
networks, municipal wireless, and other 2.4GHz wireless networks.
There have also been reports of wireless doorbells, radio remote
controls, and high power commerical VHF/UHF radios and paging xmitters
causing problems.

>We have changed the type of handheld radios we used, as
>well as turned off all the other access points (besides the symbols.).

Changed from what to what?

>I had asked about the 3Com card earlier this week in this group in hopes
>of someone helping me find a wireless nic for a laptop that can use
>promiscuous mode. I was also hoping someone might be familiar with a
>situation such as this, and make some recommendations as to how I would
>attack it. Truthfully I am at a loss at the moment.

If the intereference is coming from a non-802.11 source, Netstumbler
and the various passive sniffers will not detect anything. You might
try using Kismet on Linux to do the sniffing as it will support most
NDIS5 compatible cards. The easiest way is to use a "Live CD" such
as:
http://new.remote-exploit.org/index.php/Auditor_main
It's a huge download but worth it if you're planning to need 802.11
hacking and sniffing tools. However, my guess(tm) is that it's not
802.11 related. The consistant 10 minutes sure sounds like a
production microwave oven. You'll need a spectrum analyzer and
someone experienced to interpret the display to find the source.

>I did happen to
>have my laptop connected to one AP when the PDT6800 lost connection,
>but there was nothing there to lead me to believe that this would
>happen, and really I have no idea which direction to go from here.

What does "this would happen" mean? Did the laptop stay connected or
not when the PDT6800 lost the connection?

>It happens mostly to the AP's and PDT6800's in the back of the
>warehouse, where I have 2 aps within about 50' of each other, yet on
>different channels.

Is the back wall of the warehouse tranparent to RF? Or is the
warehouse made of steel and/or contrete? (Is it coming from inside or
outside?)

>I apologize for being so vague, if there are any specific questions that
>will help you guys diagnose this situation please do not hesitate to
>ask, and I will do my best to relay the information to you.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
> On Sun, 09 Oct 2005 22:30:10 GMT, Chris Rennert <crennert@new.rr.com>
> wrote:
>
>
>>I am having an issue with a warehouse management implementation. Here
>>is the scenario. We have 4 Symbol ap4131 access points in our
>>warehouse, and 18 PDT6800 handheld scanners. We have 2 of the AP's set
>>at channel 1, and the other 2 at channel 11. This was recommended by
>>Symbol to try and eliminate interference between the AP's. I also have
>>2 linksys 802.11G aps in the warehouse both at channel 8 , with hawking
>>Hi-gain antennas.
>
>
> The non-overlapping channels are 1, 6, and 11. The radios on channel
> 8 and 11 will somewhat interefere with each other. I would move the
> Linksys access points from 8 to 6.
>
>
>>The issue we are having is the PDT6800's are constantly dropping
>>(randomly throughout the day), and unable to reconnect for just about
>>exactly the same amount of time every single time it happens (just about
>>10 minutes).
>
>
> Look for microwave oven, 2.4GHz cordless phones, wireless security
> cameras, 2.4Ghz wireless mouse, Bluetooth phone base near the access
> points, microwave plastic pre-heater, 2.4Ghz sulphur lamp, Zigbee
> networks, municipal wireless, and other 2.4GHz wireless networks.
> There have also been reports of wireless doorbells, radio remote
> controls, and high power commerical VHF/UHF radios and paging xmitters
> causing problems.
>
>
>>We have changed the type of handheld radios we used, as
>>well as turned off all the other access points (besides the symbols.).
>
>
> Changed from what to what?
>
>
>>I had asked about the 3Com card earlier this week in this group in hopes
>>of someone helping me find a wireless nic for a laptop that can use
>>promiscuous mode. I was also hoping someone might be familiar with a
>>situation such as this, and make some recommendations as to how I would
>>attack it. Truthfully I am at a loss at the moment.
>
>
> If the intereference is coming from a non-802.11 source, Netstumbler
> and the various passive sniffers will not detect anything. You might
> try using Kismet on Linux to do the sniffing as it will support most
> NDIS5 compatible cards. The easiest way is to use a "Live CD" such
> as:
> http://new.remote-exploit.org/index.php/Auditor_main
> It's a huge download but worth it if you're planning to need 802.11
> hacking and sniffing tools. However, my guess(tm) is that it's not
> 802.11 related. The consistant 10 minutes sure sounds like a
> production microwave oven. You'll need a spectrum analyzer and
> someone experienced to interpret the display to find the source.
>
>
>>I did happen to
>>have my laptop connected to one AP when the PDT6800 lost connection,
>>but there was nothing there to lead me to believe that this would
>>happen, and really I have no idea which direction to go from here.
>
>
> What does "this would happen" mean? Did the laptop stay connected or
> not when the PDT6800 lost the connection?
>
>
>>It happens mostly to the AP's and PDT6800's in the back of the
>>warehouse, where I have 2 aps within about 50' of each other, yet on
>>different channels.
>
>
> Is the back wall of the warehouse tranparent to RF? Or is the
> warehouse made of steel and/or contrete? (Is it coming from inside or
> outside?)
>
>
>>I apologize for being so vague, if there are any specific questions that
>>will help you guys diagnose this situation please do not hesitate to
>>ask, and I will do my best to relay the information to you.
>
>
Jeff Thank you so much for all the great informatin, I apologize for not
being complete. When the PDT6800's lost connection, so did my laptop.

You mentioned microwave ovens. As far as I know the closest one to our
AP's that consistently drop are about 300+ feet away, and behind 3
separate walls. I will check and see if any of the employees possibly
have a microwaves near one of their work benches.

The building a steel building.

Thank you again, I will definitely go to that link, and grab the
software you have recommended, as well as look for someone in the area
that can do spectrum analysis.

Thanks again, and I will keep you up to date!

Chris

On Mon, 10 Oct 2005 00:59:58 GMT, Chris Rennert <crennert@new.rr.com>
wrote:

>When the PDT6800's lost connection, so did my laptop.

Probably interference of some type. What's strange is the exactly 10
minute downtime. That doesn't sound like a cafeteria microwave oven.
More like an industrial plastic molding shop with a microwave
pre-heater. Microwave ovens are also used as dryers to remove the
water from raw materials before processing. Look around for a nearby
industrial plant that might use something like this (especially near
the back wall).

>You mentioned microwave ovens. As far as I know the closest one to our
>AP's that consistently drop are about 300+ feet away, and behind 3
>separate walls. I will check and see if any of the employees possibly
>have a microwaves near one of their work benches.
>
>The building a steel building.

That means it's probably fairly well shielded against outside
influences. However, there are always windows to let in and out the
RF. Any big windows at the back wall?

>Thank you again, I will definitely go to that link, and grab the
>software you have recommended, as well as look for someone in the area
>that can do spectrum analysis.

There are cheapo spectrum analyzers that might work.
One is based on an old Proxim RangeLan2 7400 PCMCIA card.
| http://cgi.ebay.com/ws/eBayISAPI.dll...tem=5816036551
| http://www.cognetixgroup.com/products/proxim.htm

This one is not as nice, but should work:
| http://www.allaboutjake.com/network/...lanexpert.html

Here's one based on an ancient Teletronics PCMCIA card:
| http://www.odessaoffice.com/wireless/survey.htm

The problem is that these cheapo spectrum analyzers are not very
sensitive or sweep very fast. Basically, they're difficult to use
unless you exactly what you're doing. Still, it's better than
spending big dollars on renting an Agilent spectrum analyzer.

There are also relatively low cost Wi-Fi spectrum analyzers from:
| http://www.bvsystems.com/Products/WLAN/WLAN.htm
The videos at the bottom of:
| http://www.bvsystems.com/Products/WL...YJ802.11bg.htm
are worth watching to see what it's like.

>Thanks again, and I will keep you up to date!

Groan. I was afraid that would happen.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558