[asterisk-users] Migrating asterisk 11 to 13: some callers get no ringback tone any more

[Michael Maier]

Hello!


I migrated asterisk 11 to 13 as user of FreePBX 12.0.76.2.

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
  telephone system)

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.

And:
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

http://www.voip-info.org/wiki/view/Asterisk+sip+progressinband

tells:

progressinband=never

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