[Serusers] On Reply Processing Question

[Jiri Kuthan]

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