[asterisk-dev] Attended transfers and MOH

[Kevin Harwell]

Greetings,

There is a bug currently in Asterisk that essentially boils down to MOH
not being [re]started for an attended transfered call when the
transferor was listening to it.

For example, here is a specific scenario (issue ASTERISK-19499): Alice
calls Bob, Bob starts a SIP attended transfer into a confbridge that is
set to play music when empty.  Alice hears music since she is now on
hold and Bob hears music from the confbridge.  Bob then completes the
transfer and then Alice enters the confbridge, but hears no music.

This situation occurs because during the transfer and channel masquerade
the application has no way to know the channel was swapped out.  There
are a couple of ways to approach a fix for this:

1) Use a channel fixup in the applications that are affected.  A small
change to the "do masquerade" function has to be made to get this to
work too.

2) In the relevant channel drivers when an attended transfer occurs
check to see if MOH is currently playing on the transferor.  If so, once
the transfer occurs start MOH on the transferee.  This idea was put
forth by Olle Johansson (currently implemented in his
rana-moh-queue-transfer-1.8 team branch).  Albeit a few changes will
have to be made in order to use it in the main branches, but the idea
will essentially remain.

I like option 2 as it seems to be a bit less intrusive (no changes to
masquerades and such).  Also in 12+ the logic can be put into the bridge
transfer code reducing the changes further.

Thoughts? Ideas? Something I have missed or need to be aware of?

I'll start to move forward with #2 soon and put it up for review.
Comments and feedback always welcome.

Thanks!

-- 
Kevin Harwell
Digium, Inc. | Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at: http://digium.com & http://asterisk.org