What could be the reason for the 408 error in SIP connection?

Question

SIP

I connect SIP from LifeCell.
From the operator I received instructions, certificates and parameters for connecting to the SIP trunk.
Installed Zoiper, entered the settings with meticulous precision.
Here is the ZOIPER log

2016-12-17 14:44:33: Registering account '[email protected]:5061' failed, protocol_code: 408, cause_code: 102 (recovery on timer expiry).

Here is the 3CX log

12/17/2016 2:11:00 PM - [CM504005]: Registration failed for:
Lc:10000(@Lifecell [ sip:[email protected]:5061]); Cause: Cause: 408 Request Timeout/REGISTER from local

A client with ZOIPER from under NAT climbs into the world, but 3CX is static.
2 completely different conditions, but the error is the same.

Answer 1

Have you tried port 5060? 5061 looks closed.