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.
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.
Thanks, Ricardo Villa
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.
Great! Thanks Jan for your explanation.
----- Original Message ----- From: "Jan Janak" jan@iptel.org To: "Ricardo Villa" ricvil@epm.net.co Cc: serusers@lists.iptel.org Sent: Thursday, November 06, 2003 2:28 PM Subject: Re: [Serusers] On Reply Processing Question
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.
Serusers mailing list serusers@lists.iptel.org http://lists.iptel.org/mailman/listinfo/serusers
At 08:21 PM 11/6/2003, 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.
SER does not generate the ACK for a 200 -- UAC does. The ACK is (unless record-routing is deployed) send directly to UAS. That's how SIP works.
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.
Any follow-up requests either travel directly or follow record-routing logic. Strictly speaking, they follow dialog rules and a proxy server is not supposed to determine their routing on its own.
BTW -- DTMF over INFO is proprietary. There is no standard for it, Cisco gateways do so nevertheless.
-jiri
-
Jan Janak -
Jiri Kuthan -
Ricardo Villa