to start off, i will say I haven't these issues that everyone is posting...I've had spotty service. With that said, the issues I've seen have been -- sporadic connectivity over wifi calling and being able to receive or place phone calls...and then the aggrevating issue of sending/receiving texts. sometimes they will send, other times, they send immediately and quickly i might add. As for recieving texts, there are times I get them as soon as one is sent to me...other times, I get about 10 that come in at once with about a 2 hour time window in which they were sent.
Because of this, over the past 3-4 months, i have spent time in playing with settings, tweaking firewall rules etc, which this link explains it well
[ https://community.verizonwireless.com/t5/Verizon-Wireless-Services/What-are-the-wifi-calling-firewall-ports-and-destination-IP/td-p/1080659 ]
Finally, i decided to checkout the packets/the traffic etc and did some packet captures. What I noticed was it appears as tho when I immediately connect to wifi, the system sets up the ipsec tunnel. If during this time any of the aforementioned actions take place, the tunnel remains up and working. From a packet capture, it appears isakmp requests and responses are sent, tunnel keepalives and heartbeats flow as they should. However, after you drop the call, the tunnel seems to time out and for whatever issue, you start getting packet/ESP sequencing errors...during this time, I had noticed this is when the calling and texting gets to be unstable. If I disconnect from wifi, and reconnect, it appears the tunnel is renegotiated and comes back to life (provided the existing session is removed from your firewalls memory).
In conclusion, i feel the Android OS is having the issue with regards to the tunnel timing out. I want to say the tunnel times out around 5 mins of being completely active...once is disconnects the ipsec tunnel, I'm not sure if it releases any of the sessions or not it previously had, so those sessions get stuck in memory. I'd be curious to know if anyone else has looked this deep into it. If someone has, see if you can't replicate the same issues as I had/discovered. perhaps they can expand more on it or see something else i wasn't able to.
Either way -- the developers need to start looking at the way the wifi calling is done and come up with a better way of how the tunnel is kept alive...something not right here.
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