[Asterisk-Dev] IAX2 call variable passing between servers

Michael Bielicki Michael.Bielicki at Global-Gateway.net
Tue Dec 2 09:53:04 MST 2003

The idea rocks. It would also finally add a simple way to trace a call 
all through a iax network and add billing info to it.

John Todd wrote:

> Here's an idea for you all to shoot down.  I'll await the nonexistant 
> comments before I open a feature request.
> We have the luxury of moving calls around with IAX2, where we (the 
> Asterisk community) have control of the protocol.  Various hacks are 
> being installed into SIP headers to move data around, as I'm 
> experiencing with some of the installations I've now seen.  With IAX2, 
> it seems apparent that we should be able to move variables around 
> semi-transparently, since IAX2 integrates with Asterisk completely.
> Sending all variables might be difficult/insecure/silly, as we don't 
> want to clutter the call setup with a slew of variables, some of which 
> may be inherently "secure" and should not leave the server on which 
> they were generated.  Perhaps some naming convention could be used to 
> differentiate variables that would be passed to the remote end as 
> "special case" variables.
> There are two possible methods that could be used to determine if 
> certain variables might get passed.  The first method is the simplest, 
> which is to simply search all the named variables and see if any of 
> them begin with "resend." and then transmit those automatically.  
> Alternately (and perhaps, in addition to this method) one could add 
> yet another modifier to the Dial command, such as "v" which stands for 
> "send [v]ariables".
> I propose a format like this for outbound:  outbound.VARNAME
> I propose a format like this for inbound:   inbound.VARNAME
> I think that it would be wise to "sandbox" the variables with a 
> distinguishing feature (name prefix) so that we do not inadvertently 
> move variables out of or into local/remote dialplan executions.  The 
> extra two steps is a small enough effort.  (really, one step at each 
> end is needed to be "clean", but we could skip the re-translation at 
> the far end and just use ${inbound.VARNAME} if we were lazy.)
> As an example:
> exten => 123,1,SetVar(GREETING=hello there)
> exten => 123,2,SetVar(NAME=John Doe)
> exten => 123,3,SetVar(outbound.GREETING=${GREETING})
> exten => 123,4,SetVar(outbound.NUMBER=${EXTEN})
> exten => 123,5,Dial(IAX2/remote1 at hub1/${EXTEN},,v)
> Upon receiving the call, the other host (hub1) would then have to 
> translate back like this:
> [from-remote1]
> exten => _X.,1,SetVar(OURGREETING=${inbound.GREETING})
> exten => _X.,2,SetVar(DIALEDNUMBER=${inbound.NUMBER})
> exten => _X.,3,blah blah blah
> SIP:
> As far as having this work across channels other than IAX2: SIP can 
> handle almost any number of additional headers.  It could be possible 
> to incorporate a "custom" header if there are any variables that fall 
> into the 'resend.' group.  Of course, fully escaped syntax would need 
> to be followed.  As an example, a custom header could be 
> generated/parsed:
> Asterisk-Variables: FOO="hello there";NUMBER="123"
> PRI:
> There are special areas in the PRI outbound call which could contain a 
> limited number of variables passed along.  See: 
> http://www.mail-archive.com/asterisk-dev@lists.digium.com/msg01246.html
> No idea.
> No idea.
> H323:
> No idea.
> Local:
> Multiple methods: db[put/get] or native bridge variable transfers.
> JT
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