[asterisk-dev] Attended transfer while ringing using out of band signalling

[Joshua Colp]

Greetings All,

This issue was brought up internally and I'd like to throw it out there 
for discussion.

Scenario:

Person A dials a DID for Person B
Person B answers the phone and says, "hey wait... Person C would be 
better for this - hold!"
Persin B does an attended transfer to Person C. (*)
Person C's phone sends back an out of band ringing indication (180 
Ringing in SIP).
Person B completes the attended transfer before Person C picks up but 
after ringing is sent.

What does Person A now hear? Silence.

The issue comes from the fact that the control frame for ringing was 
sent to Person B but never sent to Person A. The channel then doesn't 
know to generate the ringing indication sound.

There is a "quick fix" available by looking at the state of the channel, 
but this isn't always true as some people may Answer() explicitly in 
their dialplan.

Any thoughts?

* Yes I realize it would be better to do a blind transfer and it would 
solve the issue.

-- 
Joshua Colp
Software Developer
Digium, Inc.