[Asterisk-Dev] Transfer of variables in app_dial

[Olle E. Johansson]

John Todd wrote:
> At 6:15 PM +0200 on 4/20/04, Olle E. Johansson wrote:
> 
>> In some cases, you want channel variables to be transferred from the 
>> caller to the callee.
>> This works for VXML_URL but not for other channels.
>>
>> There's a patch that transfers all variables in
>> http://bugs.digium.com/bug_view_page.php?bug_id=0000928
>>
>> I discussed this with Mark and we agreed upon a solution that we want 
>> feedback
>> on:
>>
>> * Not transfer all variables by default (as in the current patch)
>> * Transfer all variables that begin with "_" (underscore) once and
>>   remove the underscore in the new channel leg
>> * Transfer all variables that begin with "__" (two underscore)
>>   without removing anything, making it stay even if the new leg
>>   is transferred to a third leg
>>

> Hmmm... sounds like a very reasonable plan.  There are two concepts 
> here, of course: the transfer of values within Asterisk during a Local 
> transfer (which I think is already handled by using or not using the /n 
> option in Dial, IIRC) but then there is the more significant and vexing 
> problem of transferring values OUT of a particular server to a remote 
> server.
> 
Well, this patch takes care of local transfers. To explain to other readers:

When you exec dial() in the dial plan, you're in one call leg. Dial() opens
another call leg to attach your call to some other device. We now have two
call legs.

The channel variables you set with setvar is local to the current call
leg, the caller. Sometimes we want variables to be transferred to the other
leg, the callee. This patch would handle that.

John brings another topic up for discussion, actually transferring variable
names and values over the link out of band to the other end. This would be
very useful when clustering asterisk servers, transferring account codes
and other variables.

I need a solution like this to handle SIP 302 transfers, to be able to send a
transfer back to the dial plan again.

/Olle