This fix did not work for me.
After trying all the remedies I could find on-line I finally came up with a real one working with a GREAT T-Mobile support person.
T-Mobile offers a CellSpot router (TM AC-1900) that will fix the problem.
I tried it and it did eliminate the problem.
It is basically a customized Asus RT AC68U.
The modification essentially gives WiFi calling the highest priority for bandwidth on the router.
I already had an AC68U and wanted to use it instead.
If you have an AC68U, N66U, or other router that has a Traffic Manager and/or QoS (Quality of Service) settings, you can do the same thing with your own router.
Go to your Traffic Manager.
Turn QoS on.
Go to User-defined QoS Rules.
Enter the following two rules giving them a meaningful name like "WiFi Calling", enter the MAC for your phone, enter at least 85% of your available bandwidth (e.g 0-42500 if your maximum transfer rate is 50 Meg), the highest priority and:
Rule 1: Destination port "4500" Protocol "UDP"
Rule 2: Destination port "5060, 5061" Protocol "TCP"
Doing this I went from very repeatable ER081/082 to no problems at all.
Further, if you're an Xfinity user using the Xfinity wireless gateway (Model: TC8305C, in my case), your firewall needs to allow peer-to-peer applications; i.e., set your firewall to "Custom Security," and make sure that "Block Peer-to-peer applications" is NOT chosen (as well, make sure that "Block http (TCP port 80, 443)" is NOT chosen; what you choose f/ the remaining options under "Custom Security" depends on your individual firewall preference/needs).
In my situation, doing all of the following fixed the problem (note, my setup involves a master network/gateway—the Xfinity box—and a sub-network that goes through a Linksys router connected to the Xfinity box; my Note 4 connects to the internet through my sub-networked Linksys router):
- I enabled IPSec on my Linksys router (Security > VPN Passthrough).
- I left PPTP disabled on my Linksys router; as it turns out, PPTP's status—enabled or disabled—is irrelevant here.
- On my Linksys router, I implemented the QoS rules recommended here by user tedweiler (posted on Jan 15, 2015 at 4:50 PM); however, as it turns out, these QoS rules may or may not be truly necessary—time will tell.
- On my Xfinity wireless gateway, I allowed peer-to-peer applications through my firewall (as I describe at the beginning of my reply here).
- On my phone, I left "Smart network switch" enabled (Settings > Connections > Wi-Fi > Smart network switch); as it turns out, the "Smart network switch" status—enabled or disabled—is irrelevant here.
- Finally, along the way, I also cleared my phone's app caches (Settings > General > Storage > Cached Data); cleared my phone's "Wi-Fi Calling Settings" data/cache (Settings > Applications > Application Manager > All > Wi-Fi Calling Settings > Clear Data); and power-cycled my phone (i.e., toggled off Wi-Fi calling > turmed phone off > removed battery and sim card > put back in sim card and battery > turned phone back on > toggled on Wi-Fi calling). These "along the way" actions ultimately may or may not have made a difference; just know that I did them.
Bottom line, the two necessary steps (i.e., if they were not done, then there was absolutely no hope) were the following:
- enabling IPSec on my Linksys router; and
- setting my Xfinity wireless gateway's firewall to allow peer-to-peer applications.