Measuring signal strength between 2 bridges (1310s)

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Feb 11th, 2009
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Hi:

I've been experiencing sporadic connectivity issues (losing association between root & non-root bridges, cannot ping remote bridge) at one of my customer's site. I am looking for a tool that will allow me to measure signal strength or noise ratio between 2 1310 wireless bridges. Does anyone know of any tools that will allow me to gather such information? Thanks for any feedback.

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jeff.kish Thu, 02/12/2009 - 07:45
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Have you completely lost connectivity? If not, the bridges themselves can report signal strength. Simply set the bridges to "install mode". There's a checkbox for this in the web GUI under the Dot11Radio0 interface configuration. Otherwise, you can activate it on the terminal by issuing the "station-role root install-mode" or "station-role non-root install-mode" commands, also under the Dot11Radio0 interface.


Once you do this, it will flood the terminal and web GUI log with reports of the received signal strength. I'd advise that if the signal strength is close to or over -70dBm that you install higher gain antennas.


Note that performing this config may cause a small hiccup in the wireless transmission, not that it would matter much if it's going up and down constantly. But if sensitivity to this issue is important, you might want to do it after hours.

scottmac Sat, 02/14/2009 - 06:32
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As mentioned above, you can look at the RSSI values; the traditional instrument-of-choice would be something like a spectrum analyzer ($$$ - possible to rent) connected to the antenna.


A spectrum analyzer will give you a sweep of the band and show you the signal strength in terms of db(microvolts) or dBm (power relative to a milliwatt) and will also show any persistent interference. Since you are seeing the direct signal, it can also be used to tweak the aim of the antennas as well (remember that there may also be differences in elevation as well as azimuth, so check the up-down as well as the left-right).


You will usually need someone at the other end to assist in verifying that you are looking at the correct signal.


If your bridges support a mode that permit simultaneous AP & bridge operation, something like NetStumbler (free, http://www.netstumbler.com )can give you signal and interference information. I don't think it supports bridge mode signaling (it might, I don't know), that's why it might be necessary to flip on AP mode for the testing.


Good Luck

Scott


erik.edwards Sat, 02/14/2009 - 13:50
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Thanks for the reply. We recently had Cisco in & they showed me Spectrum Expert (they purchased Cognio) and this product seems to give quite an amount of data re:the 2.4 & 5 GHz spectrums. As you can tell I'm fairly new to the wireless troubleshooting. Cisco even will allow you to borrow a demo of it. I'll post back after I try this out.

Lucas Phelps Tue, 02/17/2009 - 11:15
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Log into the non-root bridge and type a show dot11 associations all command and I think it shows you the speed at which the bridges are connected. 1MB, 11 MB, 24 MB, 54 MB, etc..


That command always helped me aligned them.

erik.edwards Tue, 02/17/2009 - 11:59
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Thanks for the post. I did that command and the root-bridge is showing the non-root bridge, which is good. I recently installed a Syslog server and had the bridges report to it. I am seeing the root-bridge deauthenticating the non-root bridge (with a reason of "previous authentication no longer valid") and within a second the non-root associates back but then sometimes the root bridges drops the non-root because of "too many retries". I changed the channels it uses from 1,6,11 to 3,9 because I ran a Carrier Busy Test and saw 1,6,11 were the busiest channels. At least the non-root bridge has stayed up longer than it previously had. It seems to be working, but will need more time to tell for sure.

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