***Inter-WLC voip roaming***

[Jean Paul Enerst]

HI all,

I'd like to pick your brain in something that been bugging me for awhile now... Maybe your wise experience will help out.

Here it is, i have two sites connected over mpls and two 2504 WLC controller at the DC- two WLCs because we had an even where we were expected more 1500 people. i have a bunch of 7925G in each sites.

After added the second WLC in the same mobility group, i had noticed some voice quality issues. And it was only when 7925G device were roaming between AP from one WLC to AP in another WLC... I had read the deployment guide, and it clearly mentions that inter-roaming between WLC should work!

Well i opened a ticket with Cisco and after hours of troubleshooting and packet capture, the tech came back to me and toll me in other for the voice to work better, i have to put all APs on the same sites to one controller. For instance, my one site has 60 APs, so all these 60 APs have to be in the same controller and the rest of the APs for the other site on the other controller. So i didn't argue, i just did it. And the voice got better! And i set high availability in a way that AP will only authenticate to non-primary controller only when their primary controller is down! And thing have been working for months now.

Well last week, i upgraded the firmware of the WLC from 8.0.120.0 to 8.2... so far, so good... No issues has been reported yet! However, i have noticed that the Controller are balancing out the APs which the previous firmware was doing until i set High availability... What i mean by that is one site has 60 APs and another has about 45. So the WLC with 60 Aps keeps losing out APs to the Controller with 45 APs! Pretty much to even out the number of APs per WLC!

Now, i am wondering whether or not will have the same voice issue when roaming between AP on different WLC?

Thank you all,

Eddy

[Leo Laohoo]

Due to the nature of RTP, inter-controller roaming for voice should be avoided.

[Marco Gonzalez]

Hello Eddy,

Roaming between APs joined to different WLCs is possible and supported. There are actually some typologies based on this (salt and pepper) so, as long as your WLCs know each other via mobility and the APs know where to go in case of a failure (HA N+1) then roaming and reliability is in place.

In your case in particular roaming is not an issue but voice. The problem here is that doing inter-controller roaming will take more time that doing intra controller roaming which might cause voice issues or issues in general with time-sensitive applications. So, TACs suggestion was actually a best practice in order to avoid the delay.

If you need this type of roaming to occur (inter-controller roaming) then you need t to focus on things like proper coverage, maintain low quantity of clients per AP, guarantee high rates, low interference, high signal with good SNR and QoS.

Another problem that you have is that the phones mentioned 792X are 802.11a which can reach up to 54 Mbps and to be honest they are getting old and you might have delays due to the technology that they support (no 802.11n or 802.11ac support).

As a side note: I would not use 8.0.120.0, it is not recommended by TAC and it is susceptible to some critical bugs and a critical Security Advisory cisco-sa-20160113-wlc

you can see this here:

https://www.cisco.com/c/en/us/support/docs/wireless/wireless-lan-controller-software/200046-TAC-Recommended-AireOS.html

I hope this helps,

Marco Gonzalez