I migrated asterisk 11 to 13 as user of FreePBX 188.8.131.52.
As customer of German Telekom, I have three numbers and therefore three trunks – each number is bound to one trunk.
After migration, some callers complained about missing ringback tone:
they didn’t hear any ring tone and where surprised that they suddenly got me anyway :-). The connection afterwards was as expected.
Deeper investigation yielded, that a few caller groups have been affected by this problem:
– All POTS customers of German Telekom
– VoIP customer of T-Systems (usually companies which transfered their
Not affected have been callers like All-IP customers of German Telekom or any tested mobile caller or caller using other telecommunications companies.
To make it even more strange: Calls coming from T-Systems customer via call forwarding have been working fine, too.
The ringback tone wasn’t missing, if the second number (the second trunk) of the asterisk installation was used!
The only difference between those two trunks is: The first trunk is configured to a ring group – the second trunk is configured directly to an extension.
My solution after long time of digging around:
I added progressinband=never to sip_general_additional.conf
But this solution confuses me, because
Whenever ringing occurs, send “180 ringing” as long as “200 OK” has not yet been sent. This is the default behaviour of Asterisk.
Why do I have to provide it especially if it is the default behavior?
Why did it work without this option with asterisk 11? Why is there suddenly a difference in behavior between binding a trunk to a ring group or an extension?
Puzzled, regards, Michael Maier