Also, note that "7920 AP CAC" enables the Cisco proprietary CAC Information Element in the beacons. 7925s can see that information, because it is a CCX client. However, based on a post by a Cisco employee on one of the Cisco forums, it appears that the 792x phones no longer use that information to make roaming decisions.
Jason Boyers, CCIE #26024 (Wireless) Blog: netboyers.wordpress.com On Thu, Jan 24, 2013 at 10:10 AM, Jeff Rensink <[email protected]> wrote: > There does seem to be some conflicting info out there in the Cisco > documentation. In reality, you only need to enable 7920 AP CAC if you need > to support a mixed deployment of 7920 and 7921/7925 phones. The 7.0.116.0 > config guide link below might help shed light on the issue. > > > http://www.cisco.com/en/US/docs/wireless/controller/7.0MR1/configuration/guide/cg_wlan.html#wp1179895 > > Here is the important snippet. > > Guidelines for Configuring QBSS > > Follow these guidelines when configuring QBSS on a WLAN: > > •7920 phones are non-WMM phones with limited CAC functionality. The > phones look at the channel utilization of the access point to which they > are associated and compare that to a threshold that is beaconed by the > access point. If the channel utilization is less than the threshold, the > 7920 places a call. In contrast, 7921 phones are full-fledged WMM phones > that use traffic specifications (TSPECs) to gain access to the voice queue > before placing a phone call. The 7921 phones work well with load-based CAC, > which uses the percentage of the channel set aside for voice and tries to > limit the calls accordingly. > > Because 7921 phones support WMM and 7920 phones do not, capacity and voice > quality problems can arise if you do not properly configure both phones > when they are used in a mixed environment. To enable both 7921 and 7920 > phones to co-exist on the same network, make sure that load-based CAC and > 7920 AP CAC are both enabled on the controller and the WMM Policy is set to > Allowed. These settings become particularly important if you have many more > 7920 users than 7921 users. > > > > In regards to what to do on the lab, it is in the 7925 deployment guide as > you had pointed out. So if the task asked you to simply configure a WLAN > for 7925 best practices, I'd first ask the proctor and say there is > conflicting Cisco documentation in regards to enabling this setting. If > they don't give you any direction, I'd enable the 7920 AP CAC option since > the authoritative guide on how to configure wireless for a 7925 says to do > it. > > Jeff Rensink > > > On Thu, Jan 24, 2013 at 5:40 AM, Jeen Sern Chew <[email protected]>wrote: > >> Is "7920 AP CAC" check-box in the WLC required as best practice for the >> the 7925G phones/voice WLAN? >> >> I find this confusing because different documents says differently. I >> personally don't think it is because WMM is 802.11e standard and that is >> enough. In the 7925G deployment guide pg. 52, it says to enable "7920 AP >> CAC". I wonder if this was brought over from the 7921 phones? Both FastLane >> and IPExpert workbooks doesn't state to enable it. Another document from >> Cisco, "Voice Over Wireless LAN (VoWLAN) Troubleshooting Guide" has a >> checklist of best practice for voice. There is a task in there that states >> to make sure "7920 Client CAC" is disabled, but not about enabling "7920 AP >> CAC". >> >> I guess in the real world it would be safe to have both WMM and "7920 AP >> CAC" enabled but in the lab there's a possibility to be marked down for >> over-configuration. >> >> What is your point of view on this? Or is there something that understood >> wrongly? >> >> Thanks. >> >> Regards, >> Jeen chew >> >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, please >> visit www.ipexpert.com >> >> Are you a CCNP or CCIE and looking for a job? Check out >> www.PlatinumPlacement.com >> >> > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > >
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