Why does VoIP Yealink SIP-T21 E2 have regular beeps when calling a switched off phone?

Question

Telephony

Good day to all.
Tell me, why on VoIP Yealink SIP-T21 E2, when you call a switched off phone, the usual beeps? There is freepbx, on which there are several operators. If you poke D-Link instead of Yealink, then there is no such problem. Googled that you need to enable Early Media. But. did not help. What could be the problem?

Answer 1

Remove tcpdump dumps on freepbx in the direction of the provider + in the direction of the IP phone.
The commands are something like
tcpdump -i eth0 -n -s0 -w 'host 1.2.3.4' -w /tmp/to_provider.pcap
tcpdump -i eth1 -n -s0 -w 'host 192.168.12.34' -w /tmp/to_ipphone. pcap
where eth0 - towards the provider 1.2.3.4
eth1 - towards the IP phone [phone].
Tampas need to be removed at the same time: start, make a call, stop.
Then open both dumps in Wireshark, Telephony menu - SIP Flows. A window will open, in which you can listen to the call itself, compare what comes from the provider, what goes to the phone.
Depending on this, already look for the problem.