voice troubleshooting case debrief--SIP

Topology
SIP phone-AS5300-E1-PSTN

Symptom:
No ringback tone when calling from PSTN

Explanation:
- if the AS5300 sends a "180 Ringing", the IP phone is expected to play local ringback.
- if the AS5300 sends a "183 Session Progress", then it will cut-through early-media and the ringback will come from the PSTN switch.

Now there can be some scenarios, depending on the PI value that is send in the ISDN messaging, where we have to tweak the AS5300 behavior.

Fix:
generate the ring back tone locally in the GW by typing the command
'tone ringback alert-no-pi'
under the SIP dial peer that the call comes in on the GW.

"tone ringback alert-no-pi "
The gateway capable of providing ringback tone on the IP call leg if necessary. The tone ringback alert-no-pi command will enable this functionality, and should be used only if the PSTN switch cannot provide inband ringback tone.