Wyman_Cummings63 answered on June 10th 19 at 15:32
You have Wireshark forbidden to use?
Vern.Schneid answered on June 10th 19 at 15:34
Go to S20 via SSH, there run 2 instance of tcpdump on the external interface to the operator's side and on the inner side of the phones. Something like: tcpdump -i eth0 -n-s0 -w /tmp/dump-eth0.pcap
It is advisable to run asterisk-rvvvvv to collect data from the console. Just in case.
Next, make a test call, waiting for the "cliff" after 186 seconds. Interrupt tcpdump, download on desktop both dump open both above-mentioned Wireshark-ohms, look what happened (menu Telephony - Sip flows much help).
Question time - 186 seconds too much, not to comply with any timings SIP and interrupt the conversation. Usually 15 or 30 seconds - lost "ACK". A 186 - probably somewhere mistakenly billed duration of the call. Can be NAT loses "the stream", but then was interrupted by the voice (RTP) and the call would continue.