atcomsystems.ca/forum Forums VOIP Phones & IP PBX Networking Wireless Network Noise

Customer had an existing(in use about 1 year) wireless link between two buildings about 75 ft apart. Existing switches are 3Com. At this time, I don't know the brand of wireless, but know that it is "industrial" grade-type (not LinkSys, NetGear) It has two outside Pt to Pt antennas that are square in appearance--about 18 inches by 18 inches.

We installed a VoIP system there about two weeks ago---and last Friday the link went down. It had been very foggy that week, but at that particular time---the weather was clear. According to the event log of the VoIP system, the link was down for about two minutes. C.o. lines for the Phone System are all copper POTS.

Customers' IT tech called me the other day and said that there seemed to be a design in the wireless equipment, that when it detected "too much" noise, that it would shut down to clear it up.

We are going to be putting in fiber to fix this problem, as soon as it gets a bit warmer, but I'm curious as to this design of the equipment.

Is that a normal part of wireless equipment??

Customer has indicated that long downloads seemed to take a long time at times in the past year. If the system is shutting down for two minutes at a time---I can see why it would take so long. Thanks

Sounds like a excuse to me,if the link is good should be no noise.and 75 ft apart is not that much if in line of site

IT "professional"? My cat knows more. I asked him and he says it is probably an interference problem or a problem with the link itself. Have you checked the wireless for proper aiming, signal levels, data rate and quality? It should have a web based configuration utility that you can access from any computer on the network.

-Hal

Meow...Meow....Meow!!

Yeah, that's what I'm thinking, too. We'll get in at some time to see what the configuration is---but in the meantime---we're giving them an estimate for a fiber link.

In talking to this IT tech---our IT guys think that he doesn't really know that much--but "professional courtesy" make our guys give him the benefit of the doubt. Thanks.

75' between points? With 18x18 square antennas, which sound like patch antennas with about 9db of gain. The equipment may only be operating at 11 mbps if it is standard 802.11b gear, but it may be some proprietary stuff, which may be as low as 1 mbps.

Some questions to ask are:
How long has it been installed?
Who makes it?
Is there anything in between, trees can really kill an rf signal.
Are the antennas pointed at each other, or close, the antennas should have about 90 degrees of coverage.
The big questing is what is in between, if it is free space then they probably have noise coming from something. If there are objects in between, is there rf line of site, which is more of a football shape.

See various calculators here,
https://www.zytrax.com/tech/wireless/calc.htm

We have setup a lot of p to p wireless units, and in my opinion the biggest problem has usually been the distance between the AP and the extended antenna (directional/omni). Additionally the type of coax used between the two is critical.

As Jim suspects, it is probably outside interference. You can help reduce that and probably improve the connection by moving the AP antennas back from the edge of the roof (assuming a flat roof). This will reduce any multi-path and perhaps shield them from the interference source. You should be getting plenty of signal with the AP's only 75' apart unless they are really low power or are not 802.11 standard equipment.

As an example I get open space connects of around 900' with 200mw omnis, a noise floor of around -90db, at 5.5Mbit.

I've had problems with this before with point-to-point microwave antenna's. Basically what it amounted to was once-a-month the AC guy would go up on the roof, and move the antenna to climb around the AC. It took a while to find because he would move it, and then when he was done, move it back to about where it was, so the signal would go from strong to very very weak (since he didn't know what he was aiming for). Moving the antenna away from other things on the roof fixed the problem.

Leaves and other obstacles will obviously screw it up. I've also seen heavy fog (like black-out) really lower the signal.

When we did P to P Microwave, we fastened the antennas so that they could NOT be moved. Bolted and torqued. It helped eliminate a lot of problems.

We would also either mount them on the parapet or high enough up so that no one could walk in front of them. A little bit of a pita on installation, but a lot less grief going down the road.

Sam

Customer has decided to run fiber---we have ordered it and have it here in the shop--and also 2 media converters.

When the weather permits, we'll put it up.

Just for curiosity sake--we'll take a look at the antenna installation to see what kind of mounts they have there. The installation has been in place about 3 years---but we are finding out that there are quite a few small "down-times".

It wasn't as evident with just the network setup--however--now with the phones using the link---the anomalies are much more evident.