Unleashed WiFi Calling issues - any Unleashed protocolls / ports between the APs?

[stefan_mehre]

Hi, 
I am still facing extremly annoying issues on a customer home with 16x R350 und 4x T350d
accesspoints in the Unleashed system. I think I tryed pretty all information I found on web, but 
there is still something like a iPhone issue after time. 

I setup a 2.4 GHz SSID for the homeowner devices, because there are some corners within the 
house which have bad 5 GHz coverage. So I decided to change it to only 2.4 GHz. I tryed with 
and without 802.11r-FT-Roaming and 802.11k. I tryed different min. BSS-Rate, OFDM on and off. 
I have WiFi Calling active with the profile for German Telekom, German O2 and German Vodafone. 

We tryed to put most of the APs on one Cisco CBS350 networkswitch, but we needed to place 
some on others. So for management between the APs they need to communicate between different 
networkswitches. 

Before I tryed all new Unleashed releases with pretty the same result so I downgraded to the older 
release 200.14.6.1.203. But that one didn't solve the issue. I would say it doesn't matter this one 
or one the 200.15.xxx or 200.16.xxx oder 200.17.xx releases. But honestly I didn't try the new 
one, just released. But I don't have much hope because there is nothing in the releasenotes pointing 
in that direction. 

So the issue is:
- it seems only iPhones are facing this issue, my Android phone was much better till no issue
- sometimes WiFi Calls are working, maybe even some of them a day, but ofter WiFi calls are interrupted 
  and in many cases the user can't call again for some time
- at the moment I am not sure if that is a German Telekom only issue, because I use German Vodafone 
  but on an Android Samsung S21 and I am able to make a call and walk the complete place without 
  interruption. But the customer phones use German Telekom as provider and are iPhones of different 
  years. 

I saw that in some areas of the house the clients do connect to APs one floor higher or lower, so they switch
between APs on different networkswitches. 

This makes me thinking could there be a communication issue between the APs when they need to talk 
over an uplink between networkswitches. Is there any Unicast, Multicast, Broadcast communication which 
could be blocked accidently? 

We use a separate VLAN for all the APs and have trunk links from the Cisco Switches to the APs. So we 
can use the other VLANs within the WiFi SSIDs. We didn't see any communication issues between the 
APs, the uplinks between the Cisco switches are 10 Gbit/s. 

Honestly I run out of ideas to solve this...