Hi All:
I am involved with a project that consists of a Dialer application
talking to a SIP to TDM Gateway that supports outbound dialing and audio
detection, e.g. voice detected, modem detected, etc.
One proposal conveys the state of the TDM call from the Gateway to the
Dialer application using:
* CALL-INFO headers on 180 Ringing messages
* a user defined application document type in UPDATE messages
(before and after the SIP session is established) to convey information
like gateway detection capabilities, "modem detected", etc.
* SIP final response codes
A second proposal suggests that:
* the SIP session between the Dialer application be established
immediately using the normal SIP UAC - UAS call flow
* INFO messages be used to convey all information pertaining to
the gateways detection capabilities and the state of the TDM call using
a user defined application document type. This is similar to the
conveying of mid-call information for ISDN calls.
The first proposal uses several mechanisms to convey the state of the
gateway detection capabilities and the state of the TDM call. It also
uses the UPDATE message to convey information that does not effect the
state of the SIP session between the Dialer and the Gateway. The first
proposal also uses the UPDATE message after the SIP session has been
established.
The second proposal uses a much simpler mechanism for conveying the
gateway detection capabilities and TDM call state. However the use of
the INFO message does require an additional message exchange to convey
information that appears in the 180 Ringing message in the first
proposal.
The questions I have are:
* Which proposal seems more in keeping with the spirit of SIP?
* Is it more correct to tie the SIP session state to the state of
the TDM call or to separate them?
* Are there other instances of this kind of use case that I could
reference?
Thank you all in advance,
-Rick
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