Incoming calls end after 2 mins 5 secs

[DanielMy_399855]

I have a recurring issue with incoming calls ending at exactly 2 mins 5 secs. Its repeatable until I place an outgoing call, which works as expected, after placing an outgoing call usually incoming calls will work for a few hours before the issue reoccurs.

When the call ends, the phone does not report the call has ended, it just returns to the home screen. The phone placing the outgoing call (tested from Vodafone and O2 gets a 'Call Ended' message).

I've tested my SIM on two phones (Motorola Edge 40 Neo, Moto G14), and found that the issue occurs on both, and once it starts it repeats until I either restart the phone, or place an outgoing call.

Any ideas on what the cause could be?

I couldn't find any posts of the same issue on the Smarty forum, but could find the exact same issue reported by an ID Mobile customer (ID Mobile being a Three MVNO the same as Smarty) here: https://community.idmobile.co.uk/device-phone-support-26/incoming-calls-cut-off-after-2min-5sec-5772...

[Michael_2408837]

I'm also having this issue and it's damned annoying. Have no idea how to stop it. Restarting the phone seems to stop it but eventually the problem returns. 

[SmartyTrousers]

I've read about a similar issue on Vodafone some time ago, although in that case it was after 29 minutes and 50 seconds. Still, I think it could be the same issue and it's just that different networks set different timeouts.

The issue seems to be that on 4G calls (and I think WiFi calls) the network requires the handset to periodically send in a keep-alive message during the call, to let the network know that the call is still active. And some Android handsets send the keep-alive signal in a format the network equipment doesn't recognise.

So I'm guessing Three's/Smarty's network tells the handset to send the keep-alive message every 2 minutes. Your handsets are probably doing this, but in a format the network doesn't recognise. So after waiting a few seconds' grace period, the network decides it hasn't received a valid keep-alive message, so the call must be over.

I believe this is why Smarty has a list of devices which are not compatible with its 4G calling here. The two Motorola devices you have tested are not listed, but maybe Smarty's list isn't comprehensive.

Here's a discussion on Reddit which goes into technical detail about the issue which was occurring on Vodafone.