[Serusers] On Reply Processing Question

Jan Janak jan at iptel.org
Thu Nov 6 20:28:03 CET 2003


Hello,

On 06-11 14:21, Ricardo Villa wrote:
> Hi,
> 
> The manual explains that we can use "t_on_failure" and "failure_route"
> primitives to route a SIP request to another destination if the original
> destination does not answer.  It is very clear to me how this would work for
> an INVITE message which receives a confirmation from the far end (like
> "Trying").   But when the call is established, the originating party sends
> an ACK message which is not supposed to receive a reply.  How does SER know
> where to send this ACK to??  Does it again try the first destination?  If so
> then the message will be lost.
 
  No, the ACK is a mid-dialog request and therefore it will be routed
  using record routing. That means Request-URI will not contain URI
  belonging to the server but the contact of the callee (from 200 OK from
  the callee), that's how SER knows where to send ACK requests. The
  routing logic in the ser.cfg file is not applied to ACKs.

> And how about INFO messages (like those used to send DTMF tones).  Lets say
> a call is established to a backup gateway using "failure_route".  Then the
> user sends a DTMF tone as an INFO message (maybe he called an IVR).  How
> does SER know that this INFO message must go to the backup gateway?  If SER
> tries the main gateway first for every single DTMF digit pressed then this
> is not going to work properly.

  The same story here. INFO messages in this case are sent within the
  dialog created by INVITE and thus they will be routed using record
  routing.

  The same for the final BYE.

  In you switch off record routing on your server then ser will not even
  see such messages because they will be sent directly from the caller
  to the callee.

   Jan.




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