Follow me - Cell phone keeps ringing after call is answered locally on IP Phone

Weird one here:

I have an extension with a follow me configuration as follow:
Initial Ring Time: 2 seconds (short, I know)
Ring Strategy: ringallv2-prim
Follow-Me Ring Time: 30 seconds
Follow-Me List: extension (2XX) + cell phone number (with # at the end of the number)

When a call comes-in (local or external, no difference), the person answers the call after one ring on the physical IP phone. Even though the call is answered, the cellphone starts to rings and keeps ringing until it reaches the Follow-Me Ring Time of 30 seconds. The hang up signal seems to be lost along the way.

I will try to reproduce the issue and get some logs. Has anyone ever experienced this ?
I manage around 60 systems with a lot of them using the same kind of setup and I’ve never seen this. I wonder if it could be related to the cell phone’s carrier.

Some trunking providers have a bug where if CANCEL is received in a small window after the initial INVITE (e.g. 500 milliseconds), they give a 200 response to the CANCEL but don’t actually cancel the call. Sorry, I don’t remember what software has this bug. Using
pjsip set logger on
sip set debug on
you should be able to see this in your log.

Short of modifying the source code for Asterisk, I don’t see a good workaround.

Setting the Initial Ring Time to e.g. 6 seconds should greatly reduce the number of incidents; most calls would be answered either before that or long after.

If you have multiple trunking providers, choosing a different one for first priority on these calls may fix the problem, or choosing a different sequence of upstream carriers (if supported by the provider).

If the mobile in question has good data coverage, sending the call to a SIP app instead of cellular voice may make sense. That also fixes the false ‘missed call’ shown on the mobile when the call is taken on the desk phone.

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That makes a lot of sense, thank you ! I will try to change the Initial ring time and see what happens.

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