SIP over VPN for some reason breaks connections?

Question

SIP

And hello again ....
the task is to transfer the SIP stream from the provider brought to the branch to the central office.
available:

at the central office there is a PBX (10.20.10.17) a SIP provider is available through the tunnel between departments, its equipment is visible, it connects for several minutes and then the connection breaks (and the connection breaks not only if the connection is made in the PBX, but also if you connect an account to the SIP phone It also doesn’t last long. It
helps but not for long if I break the connection.
(I tried turning the sip port service off and on, it doesn’t help), tell me how to make the connection work stably?
The connection between the central office is stable and internal telephony works fine,
from the central office through the branch to the router of the SIP server ping stable

Packet exchange from 10.10.10.1 to 32 bytes of data:
Reply from 10.10.10.1: number of bytes=32 time=33ms TTL=253
Reply from 10.10.10.1: number of bytes=32 time=32ms TTL=253
Reply from 10.10.10.1: number of bytes=32 time=32ms TTL=253
Reply from 10.10.10.1: number of bytes=32 time=33ms TTL=253
Reply from 10.10.10.1: number of bytes=32 time=33ms TTL=253
Reply from 10.10.10.1: number of bytes =32 time=41ms TTL=253
Response from 10.10.10.1: number of bytes=32 time=32ms TTL=253
Response from 10.10.10.1: number of bytes=32 time=32ms TTL=253

Answer 1

From the office, a SIP client with the same settings (like PBX) works correctly, does it not fall off?
It seems that you need to configure PBX for your provider. If the VPN works, then there can be no problems.
I suggest testing your projects first directly, then complicate the tasks by adding VPN and other technologies.

Answer 2

How do you prioritize traffic?
what do you have in the mangle?

Answer 3

Uncheck the Firewall - Service ports - SIP tab, and also disable this line. Perhaps the mechanism for supporting SIP connections is working, it conflicts with some *.