We are planning to change the PSTN connection from ISDN to SIP.
We have the following equipments:
CP7941 (with SCCP)
Cisco2851 as IOS voice gateway (C2800NM-SPSERVICESK9-M), Version 12.4(22)T)
The current call process is the following:
7941 -SCCP-> CUCM -H.323-> Cisco2851 -ISDN-> Telco
We do not have any problem via ISDN. The ringback tone from Cisco2851 to 7941 goes in audio mode (in RTP).
The planned and tested call process is the following:
7941 -SCCP-> CUCM -H.323-> Cisco2851 -SIP -> Telco
We found that no Ringback tone on the IP phone while calling to PSTN via SIP provider but the phone displayed âRing outâ message.
We make several debugs, and we saw that Telco sent us âSIP/2.0 180 Ringingâ and Cisco2851 sent âALERTINGâ to CUCM while was not âRingback toneâ on calling phone.
What special setting is necessary to get âRingback toneâ on IP phone if the SIP provider sends Ringing message?
Is there any possibility to make IP Phone to generate âRingback toneâ?