802.11n and EDCA -versus- 9971/7925 deployment guides

[Kayle Miller]

So I was re-reviewing the deployments guides today for the 9971 & 7925 WiFi phones when I noticed that Cisco reccomends changing the EDCA Parameter from WMM to Voice Optimized. It is my understanding and the hitting apply re-affirms that belief that if you change it to Voice Optimized that it will disable the 802.11n data rates. Can someone confirm this is correct and if so then what is the Cisco best practice to for an 802.11n deployment for this setting? should it just be left at the default of WMM?

I also noticed it says to enable the 7920 AP CAC on the WLAN but I thought that was best left un-checked?

please provide me with any thoughts or feedback.

Thanks,

[Raul Manzano Barroso]

I supposed you must enable AP cac if you need compatibility with 7920 phone in this deployment; if not, uncheck this option. I refer to 7921G deployment guide.

Best regards.

[Kayle Miller]

Raul,

     Actually the 7921G Guide says almost verbatium what the other 2 state in regards to that, it simply says to enable the 7920 AP CAC; actually all of the questions I posed above are virtually identically documented in all 3 Deployment guides all 3 of which were updated around the same time.

     This is what has cause the question to be asked, how should this stuff be set since like you said the 7920 AP CAC is only supposed to be for 7920 phones not 792x phones.

Thanks,

[Nicolas Darchis]

AP CAC is advised even for deployments not having 7920s. It is a "it doesn't hurt" feature which adds the current AP load in the QBSS. This is an information that phones can use.

It was originally for the 7920 but is used by all phones.

7920 client CAC is really only for 7920 and is non-standard. So advised to stay disabled.

The WMM/Voice optimized setting is mainly optimising the prioritising of traffic through different timers. If you want 11N, you can leave WMM optimized and it will also work fine with phones.

Nicolas

[Kayle Miller]

Nicolas,

     Thanks for the info. It's one of those things that clients see it in the deployment guides and they want to know why their environment is not configured exactly as the deployment guide states.  Is there any Cisco document that goes into more detail on those components??

    Thanks,

Kayle

[Nicolas Darchis]

Unfortunately, the Voice deisgn guide 4.1 would need some dust-cleaning to cover topics like this one in more details ... So no good documentation that I'm aware of.

Nicolas

[Raul Manzano Barroso]

Hi kayle.

Thanks for your answer. Its very interesting.

I talked yesterday about this because I red three days ago the Enterprise Mobility Design Guide 4.1; It describes that AP CAC is a "Cisco IE" and you can include the appropiate QOS element in your SSID to sent the neccesaryu information for your QoS devices in this SSID.

Because You talked about only the 7925 an 9971 I understand you only used this two devices and I thought you don´t have to add the "Cisco IE " element en QBSS; these devices work with new QBSS (802.11e standard). I think a cleaner SSID configuration always is better 

Good question about 802.11n and WMM and / or Voice optimized.

Best Regards.

[Kayle Miller]

Raul,

     Thanks for the responses, I agree with you whole heartedly and I don't normally enable the 7920 cac options when I do a voice SSID, but I have had the question come up from clients why it's not set and the deployment guide says it should be. So I wanted to get feedback from others as to how and why they do or don't enable those features. Plus asking the questions enables more of us to collaberate on the subject and may provide unique insight into it.

Thanks,

Kayle

[migilles · Accepted solution]

Yes it is preferred to use voice optimized or voice and video optimized, however it is also ok to use WMM for the EDCA profile.

I also brought up the question recently about the popup window that displays if you change from WMM to something else about 802.11n rates being disabled.

However, I know that my MacBook Pro can connect at 802.11n rates when set to something other than WMM for EDCA.  This is basically just adjusting the contention window settings.

I brought up this question as I will have to provide a deployment guide for Cius, which will be 802.11n capable.

As for 7920 AP CAC, I explain in the QBSS section of the 792x Deployment Guides what the differences are between 7920 AP CAC and 7920 Client CAC.  BAsically as someone pointed out, 7920 Client CAC is legacy, where it is not load based to account for other APs or interferers on the same channel.  7920 AP CAC is load based like the 802.11e version.  We do not use QBSS any longer for a potential roaming trigger with the Cisco 792x phones.  It is just displayed for informational purposes.  If you have WMM set to allowed or required, which it should be, regardless of 7920 AP or Client CAC being enabled, QBSS will still be sent out.  The difference between QBSS sent out with 7920 AP CAC and with WMM enabled is that the 7920 AP CAC is the Cisco implementation and has a configurable max threshold, which could be used for roaming, but since the 792x phone doesn't use QBSS for roaming purposes, it is not a hard requirement to enable 7920 AP CAC.