Will the 7921 choose a best AP based on congestion

[ericn8484_2]

I believe an AP can handle around 15 7921 phones using the wireless A standard before voice quality problems becomes an issue.

If we put two AP with different channel using A near one another, are the 7921 phones capable of load balancing between the two AP's so they dont all join one access point?

We are using Cisco AP's, with 4400 controllers and WCS.

Thanks

[Georgios Nikitas · Accepted solution]

Of course they do. The APs transmit their load in their beacons. So the 7921s know which AP is more loaded than the other one. Also, the controllers try to load-balance even non-cisco wireless devices by denying (once) a device to connect to the AP that is very loaded. Then the client will (normally) try to connect to the second AP.

[ericn8484_2]

Is there a place in WCS that I can adjust the level at which the phones should adjust? Right now I usually see up to 15 devices, but I would rather limit the phones to around 10 if possible.

[Georgios Nikitas]

Loadbalancing on the controller must be disabled. The Cisco wireless IP phones have their own algorithm for determining balance. Leaving aggressive loadbalancing enabled can create association flapping.

Note: Aggressive loadbalancing is enabled by default and can be disabled from the controller web interface or the cli with the command:

config load-balancing status disable

[ericn8484_2]

We do have aggressive load balanacing disabled.

Thanks for your help.

[migilles]

Yes Load Balancing should be disabled, otherwise the AP may reject a roam that the client has decided to make. The 7921 makes the roaming decisions and uses signal, QBSS and PER (packet error rate) to make roaming decisions. Can also roam to an available AP if CAC (TSPEC) is enabled and the connection is refused. So if the QBSS threshold is met, the phone can roam.

We support up to 27 bi-directional RTP streams (27 7921 on call) when communicating at 24 Mbps or higher. This is with < 1% packet loss and no background data traffic. If using static CAC, the cutoff is 20 calls. Can get up to 13 at 6 Mbps.