Map ISDN Call Proceeding to SIP 183
With the introduction of the MAP ISDN Call Proceeding to SIP 183 functionality, the Call Proceeding message from the ISDN side will be interworked into a 183 Session Progress with SDP message when the value of the Progress Indicator parameter in the Call Proceeding message is either "1" or "8". By interworking these parameters, an early voice path can be established so the caller can hear a prompt played by the terminating endpoint. If no progress indicator is present or the value of the ISDN Progress Indicator is not "1" or "8" then the call will proceed as normal. The Call Proceeding message will be dropped and no SIP 183 Session Progress will be sent. Refer to the information below for more information.
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Example 1 - Receiving ISDN Progress after CALL PROCEEDING
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The IMG 2020 receives a SIP INVITE from SIP network and sends the SETUP message to the ISDN network. The IMG 2020 receives a CALL PROCEEDING with Progress Indicator No. 1 or No. 8. The IMG 2020 will send 183 Progress message back to the SIP network and a voice path is established. The Caller from the SIP network can hear the prompt being played from the ISDN side. On receipt of ISDN PROGRESS message with Progress Indicator No.1 or No.8, the IMG 2020 will send another 183 Session Progress with SDP back to the SIP network and caller will continue to hear the prompt which is sent from the ISDN network. The IMG 2020 then receives the ISDN CONNECT message and sends a 200 OK back to SIP network.
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Example 2 - Receiving ISDN CONNECT after CALL PROCEEDING
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The IMG 2020 receives a SIP INVITE from the SIP network and sends a SETUP message to the ISDN network. The IMG 2020 receives a CALL PROCEEDING with Progress Indicator No. 1 or No. 8. The IMG 2020 will send 183 Progress message back to SIP network and voice path is established. The Caller from the SIP network can hear the prompt being played from the ISDN side. The IMG 2020 then receives the ISDN CONNECT message and sends a 200 OK back to the SIP network.
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Example 3 - Receiving ISDN ALERTING after CALL PROCEEDING
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The IMG 2020 receives a SIP INVITE from SIP network and sends the SETUP message to the ISDN network. The IMG 2020 receives a CALL PROCEEDING with Progress Indicator No. 1 or No. 8. The IMG 2020 will send 183 Progress message back to SIP network and voice path is established. The Caller from the SIP network can hear the prompt being played from the ISDN side. On receipt of an ALERTING message, the IMG 2020 will not send any message back to the SIP network and the caller will continue to hear the same ring back tone. The IMG 2020 then receives the ISDN CONNECT message and sends a 200 OK back to SIP network.
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Example 4 - Receiving ISDN CALL PROCEEDING
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The IMG 2020 receives a SIP INVITE from the SIP network and sends a SETUP message to the ISDN network. The IMG 2020 receives a CALL PROCEEDING without any Progress Indicator or the Progress Indicator is not No.1 or No.8. The IMG 2020 will not send any message back to the SIP network On receipt of the ISDN ALERTING message, the IMG 2020 will send a 180 Ringing back to the SIP side. On receipt of the ISDN CONNECT message, the IMG 2020 sends a 200 OK back to the SIP network.
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