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Intercom over Wifi problems
karageur
Posts: 97
Hi guys!
I need an advice about this pretty simple intercom system.
There are NI4100, two MVP-8400i configured to work in roaming on the same 11th channel and two WAP spots working on the same 11th channel with the same SSID names - "amx" and allocated in the same LAN.
The problem shows up when the TPs are connected to the different WAPs. Intercom messages stops to transmit/receive. Though the TPs stay online and diag shows their activity. And if the TPs begin to work on the same WAP - everything goes normal and intercom works.
Does anyone see anything familiar with this issue and can advice something?
A lot of thanks in advance!
I need an advice about this pretty simple intercom system.
There are NI4100, two MVP-8400i configured to work in roaming on the same 11th channel and two WAP spots working on the same 11th channel with the same SSID names - "amx" and allocated in the same LAN.
The problem shows up when the TPs are connected to the different WAPs. Intercom messages stops to transmit/receive. Though the TPs stay online and diag shows their activity. And if the TPs begin to work on the same WAP - everything goes normal and intercom works.
Does anyone see anything familiar with this issue and can advice something?
A lot of thanks in advance!
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You have two RF transmitters transmiting on the same frequency. They will interfere with each other. That would definitely cause a problem.
It's best to put them on frequencies that are far away from each other as possible.
1 and 11 is optimal. However, you may have other devices in the house that are broadcasting in that range. Best thing to do is take some kind of RF spectrum analyzer and get a picture of what's going on. If you don't have one, you can make a good guess by using some kind of WIFI spying software on a laptop.
There are 15 meters and a bearing wall between two WAPs. When one of the TPs is in range of another WAP it automatically switches to this WAP because it has stronger signal. Strange that control signals like push, release etc come through but not intercom until two TPs are on the same WAP.
I should try playing with roaming settings and channel number and post the results of manipulations.
Thanks for advice!
Actually, it has more to do with the distance of the two waps from the TP.
a small thought experiment... Assume an open air run with no intervening obstructions...
If the TP is 30 meters from WAP A and 20 meters from WAP B, WAP B will be stronger. However, if WAP A's signal is only lower by 5-10db at the TP, then WAP A's signal is strong enough to interfere with the connection to WAP B. It will manifest itself with slow data rates or lots of dropped packets.
If you've ever seen this on an RF spectrum analyzer, you'd see that there needs to be a pretty significant distance of TP to WAP A vs. TP to WAP B for the interference to be low enough to not have an effect.
It's just best to put them on different channels and keep the channels far apart as possible.
Beleive it or not, the same WAP can interfere with itself if you have strong enough reflections in a building.
You could try connecting to the panels from your computer as well and verify that the computer can talk with both panels when they are on separate APs.
Jeff
A spectrum analyzer would help you find if there are other signals stepping on your access points (or even something as innocent seeming as a microwave ... I even had a case once where a cell phone broke a panel connection, but only if it was in use - pick up the phone, panel died). If you don't have one, at the least something like Netstumbler will tell you if there are other WAP's in range that might also be interfering.
Something that hasn't come up: are you using static IP's in all the panels? It is possible to have a good enough signal to connect to the WAP, but not good enough to negotiate the DHCP exchanges. Static IP's will circumvent that to a certain degree. But I have also found that some switches don't update their routing tables very well, and disconnecting and reconnecting a devices doesn't always restore communications until you reboot the switch. In that case, you need a switch that handles things better.
The problem is there are too many potential problems. Narrowing it down to the real one is going to be a pain.
Jeff
Yes, i use static IP. The whole preinstallation takes place in my office which is -1 floor and i use local network for this task to runaway two WAPs as long as possible from each other.
I didn't try any analyzers, but i definitely would. Two TPs show "Excellent" connection and there is no any other WAPs around in a basement.
Also didn't try to connect via telnet because i wasn't sure if it was really needed? Every push of a button and any other actions are shown in Diagnostics.
One more interesting thing i have faced with: when the TPs are on different WAPs and i push a button to begin an intercom session the speaker in my TP begins to click like it accepts the command to begin a session but mic seems to be dead on every TP. Strange behavior..
I shall test all your suggestions.
Thanks again.
If they have any 2.4 Ghz wireles telephones or any wireless VOIP phones, they could be the source of the problem. I've actually seen a case of a refrigerator putting out a huge signal that was killing the whole center of a home.
We found that with an RF spec analyzer.
It turned out that it had a microprocessor in it that was causig the problem.
I also just found this little note regarding their multi-cell installations. First time I've seen them acknowledge the problem so maybe they're working on the conversoin as we speak.
Seems ironic that the homes that use the phone system generally need a 1/2 dozen APs or more so the idea of using only channel 9 is obsurd besides the fact that the so called roaming capability requires using ONLY channels 1,6 & 9 since AMX fails to acknowledge that in the real world other channels are often more appropriate for WAPs.
For what it's worth, I have several projects with the Panasonic cells co-existing just fine with the wireless networks. I know there is a potential problem sharing those frequencies, but in actual installations, it has never been a problem. I've had far more problems in systems without the Panasonic present ... most of which have been solved by moving around the access point until I found a location that was solid.
There was a good post last year where the poster ran some tests while the customer went on an extended vacation. They monitored offline event (I think) over several days with various configurations. Again this is from memory because I couldn't find the post but when the cordless phones were powered on and all cell station active they registered around 50 offline events for a TP over a 2 day period. With the cell stations active and the cell phones turned off they had maybe 25 offline events in the same time period and then when they had all the cell phones & cell stations off they and 1 offline event in that period of time. So something is causing an adverse reaction in the TPs.
I've had jobs where placement of the phones and WAPs had to be changed because the way is was drove the customers nuts with the TP being offline quitte alot and any time you're in the middle of something and the panel drops offline they have a right to get pissed. In one particular situation the cell phone base was 10' from the couch where the TP usually sat, when the customers were home they often had the phone with them on the couch and often would be talking on the phone. My WAPs were far enough away but the TP ended up pretty evenly centered between the two of them and it couldn' make up its mind on which one it should connect to. Was it just placement of the WAPs or did the cell phone contribute to the problem? I've since decided that WAP placement should 1st be given to the rooms that will normally contain a wireles TP and then I fill in the gaps through out the house to provide complete wi-fi coverage for laptops. Then I determine cell station locations by 1st going as far as possible from the rooms with wireless TPs and then keep them as far away as possible to the WAPs.
Since the phones do freuqency hopping when they're used it's like playing the slot machines, you turn on the phone and the TPs may work but you also might get lemons. If they could shift to the 1.9GHZ spectrum it would just eliminate the possiblity of interference.