[asterisk-users] Hanging up a 3-way conference when middle user hangs up

[Lex Lethol]

Apparently asterisk's default way to a 3-way conference lets the user
in the middle hangup and the other parties stay on the conversation.
This is great some times but it creates quite a bit of problems when
trunks dont have disconnect supervision or when trying to do
accounting and billing on the user.

Here is the 'normal' situation when a user tries the setup a 3 way
conference once the user is already on the phone with someone he
called.

1.  Press 'Flash' on the phone. Party B will now be placed on hold and
you will hear a dial tone.
2. Dial party C's number or a pre-configured speed dial followed by
'#', (you can engage in conversation).
3. Press 'Flash' to join both C and B to a single conference.
4. When you place the phone's handset on-hook, party B and party C
will remain in conversation.

After step 4, B and C remain on the conversation and I am looking for
a way to disable this without disabling 3 way calling.  Basically I am
looking for a way to force asterisk hang up both B and C once the
'middle' user hangs up so this will not leave channels stuck on trunks
without disconnect supervision.

Anyone know how to accomplish this?  Any comments appreciated.