I'm troubleshooting an event where calls drop automatically after been ringing at any extension without been answered for exactly 60 seconds. This also happens with Hunt Group type extensions where circular hunting among included extensions passed the total time of 60 seconds.

It happens only at SIP trunk inbound calls, not outbound, nor in ext-to-ext internal calls. This proves somehow is not a phone device parameter.
SIP trunk provider had verified several times that their ring-timeout parameter at their side is 5mins, not 60 seconds, as its happening for SIP Inbound calls only.

Possibilities I think are:
1. A PBX extension parameter in the configured extension for the SIP trunk registration.
2. Even though SIP trunk inbound calls are ringing normally at start, customer's Firewall that is monitoring traffic activity, could be dropping the session during ringing after the first 60 seconds.
3. Even though ITSP states trunk is configured for 5mins ring-timeout, they still could be missing something at their configuration. But because is not happening for outbound calls, right now this looks less likely.

All extensions tested has voicemail disabled and still happens even if the "No Answer Timeout" is more than 60 seconds. Telephony is provided at QX's WAN port. QX's LAN port is not used. It's a QX200 (FW:6.1.45) with SNOM 710/760 phones (FW:

One question could be...

Is there any configuration parameter at the QX extension configuration level that controls ringing timeout within the SIP operation? A parameter outside FXO/FXS/T1/ISDN types of operations.