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Wireless VoIP multipath issues: lowest datarate 12 or 24Mb/s?

Trying to solve some issues which seems to be related to multipath issues (high CRC error counters, good coverage, hardly any co-channel interference, 5GHz) in a healthcare environment, I'm planning to lower the TX-power, but I'm also considering decreasing my cell size (for the clients, not for RF energy, I know )  by making 24Mb/s the lowest mandatory data rate instead of 12Mb/s currently.

I'm a little bit unsure about this datarate because the deployment guides are describing 24Mb/s as the minimum data rate, while for example the WLC Config Analyzer recommends 12Mb/s (because of multicasting??).

Any good ideas would be appreciated. Setup is 2*WiSM2 and 2*WLC5508, 3602 APs, software 7.2.103.0.

Regards,

Johan

3 REPLIES
Hall of Fame Super Silver

Wireless VoIP multipath issues: lowest datarate 12 or 24Mb/s?

Well, are you using multicast?  I really don't think that it will affect multicast as long as the site survey was done correctly.  Setting the 24mbps is kind of high, and really doesn't eliminate multipath issues.  Yes you will shrink your cell size, but if the survey was done with the required spec, you should not have an issue.  What VoIP are you using.... Vocera or 7925's.  If running the 7925, make sure your on the 1.4(2) firmware.  Vocera only runs on the 2.4ghz, so since your talking aobut the 5ghz, I guess this isn't your issue, but just wanted to check.

-Scott
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New Member

Re: Wireless VoIP multipath issues: lowest datarate 12 or 24Mb/s

Multicast is sent at the highest mandatory data rate, if you have more than one. The only possible issue i can see if you set 24mbit/s is that some distant clients cannot decode multicast/unicast… but i think thats obvious

Like scott wrote before, i dont think that disabling 12mbit/s solves your problem.

Have you compared the FCS values in different floors or part of the building? Do you have a large number of errors everywhere?

Habe you thought about non-802.11 interference? cameras, MRT, microwave...

Sent from Cisco Technical Support iPhone App

New Member

Wireless VoIP multipath issues: lowest datarate 12 or 24Mb/s?

Thanks for the replies!

Currently we're not using multicast, but the WLAN is designed to support multicast in the next year(s). I see I forgot to mention the VoIP handsets, but you're right on the model: 7925, and we're running 1.4(2).

I've compared the FCS errors to other parts of the building, and they are higher at the APs in this particular spot. No extreme differences, but on average they are higher. We've done a lot of spectrum analysis, and since a few weeks we're using CleanAir/MSE to detect and locate non WiFi interference. Found some 2.4GHz interferers, but none at 5GHz.

Good to have you opinions on disabling the lower datarates, I think I'll stick to lowering the TX-power first to see what it does. What do you use as indicators for multipath errors? Just FCS errors, or do you have other usable indicators?

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