Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping

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RFC 3398                  ISUP to SIP Mapping              December 2002


   In SIP bridging situations (when the INVITE that initiated this
   session contained legitimate and comprehensible encapsulated ISUP),
   the CPG SHOULD be sent in the body of a particular 18x response,
   determined from the CPG Event Code as follows:

   ISUP event code                         SIP response
   ----------------                        ------------
   1 Alerting                              180 Ringing
   2 Progress                              183 Session progress
   3 In-band information                   183 Session progress
   4 Call forward; line busy               181 Call is being forwarded
   5 Call forward; no reply                181 Call is being forwarded
   6 Call forward; unconditional           181 Call is being forwarded
   - (no event code present)               183 Session progress

   Note that if the CPG does not indicate "Alerting," the current state
   will not change.

7.3 ACK received

   At this stage, the call is fully connected and the conversation can
   take place.  No ISUP message should be sent by the gateway when an
   ACK is received.

8. ISUP to SIP Mapping

8.1 ISUP to SIP Call Flows

   The following call flows illustrate the order of messages in typical
   success and error cases when setting up a call initiated from the
   PSTN network.  "100 Trying" acknowledgements to INVITE requests are
   not depicted, since their presence is optional.

   In these diagrams, all call signaling (SIP, ISUP) is going to and
   from the MGC; media handling (e.g., audio cut-through, trunk freeing)
   is being performed by the MG, under the control of the MGC.  For the
   purpose of simplicity, these are shown as a single node, labeled
   "MGC/MG".













Camarillo, et. al.          Standards Track                    [Page 30]