Generally, the IETF has not spent a lot of time on the specifics of how a PSAP without an IP connection handles a call that originated in an IP network. So, the IETF documents would just treat the MGCF in your diagram as the PSAP, and whatever it does to get to the PSTN connected PSAP is up to it.
The ecrit LoST protocol describes how the AP learns the dialing sequence for its location. We have another document that describes how emergency calls are marked (urn:service:sos where there is a single emergency number). LoST also describes how calls should route to the proper PSAP. So if the AP does digit analysis, it would obtain the dialing string(s) to look for from LoST. Once it found one, it would signal with the service URN (in the R-URI) and the PSAP URI obtained from LoST in a Route header. It is difficult for the AS (or MGCF) to do the digit analysis, because it would need to know the location of the AP to determine what to look for. If the network forces the AS to be in a visited network, that may not be so hard, but few networks can guarantee that will always be the case. That is why the IETF recommends the AP do the digit analysis and provides the LoST dial Service number mechanism. Brian ________________________________________ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of NC Reddy Sent: Friday, February 29, 2008 4:15 PM To: [EMAIL PROTECTED] Cc: [email protected] Subject: [Ecrit] Query: How to derive Emergency Call from SIP INVITE Message Hi, I have the following queries regarding emergency call interpretation at SIP Application Server (SIP-AS). scenario: ======== AP- Access Point AS - SIP Application server MGCF - Media Gateway Control Function (Softswitch ) PSAP - Public Safety Answering Point AP<----SIP--->AS<---SIP----->MGCF<----Non-SIP---->PSAP Use case1 : When subscriber(AP) makes emergency call to PSAP (AP ------->PSAP) Use case2 : When PSAP callbacks to subscriber. (PSAP ------->AP) Now Questions related the mechanisms for analyzing the emergency calls at SIP Application Server. By considering the cases of emergency call numbers are different in different countries and context. Option 1: SIP-AS can do the digit analysis from request uri of the userpart (ex: 911) and figureout the call as emeregncy and handle the call. Option 2 : If the AP/MGCF done the digit analysis and add the "priority : emergency" header, SIP-AS can rely on that header and route the call. So which option is suitable in context of SIP-AS implementation for emeregency calls. Thanks in advance. Regards Channa _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
