voice dial-peer # pots

  progress_ind alert enable 8

  progress_ind setup enable 3

Note: For Cisco IOS software releases earlier than 12.2(1) or 12.2(2)T, only the progress_ind alert enable 8 command is supported, and is normally sufficient. These commands are hidden in some Cisco IOS software releases.

Background:

• The experience is that the caller does not hear a ring on the phone of the called party, but suddenly someone answers the phone. In this case, an IP phone user calls a PSTN user.
• Since Cisco CallManager cannot provide ringback to the IP phone, it relies on the PSTN switch to provide ringback inband.
• The outbound call must include a PI of 3, indicating that the originating device is non-ISDN, and that ringback must be provided inband by the PSTN. The progress_ind setup enable 3 command ensures this behaviour.
• The return alert message from the PSTN must then include a PI of 8, which indicates to the originating gateway that inband information, in this case ringback tone, is on its way, and that the call must be cut through in the reverse direction so that this information can be heard at the origin.
• If the return alert message does not include a PI of 8, the progress_ind alert enable 8 command can be inserted into the Plain Old Telephone Service (POTS) dial peer and makes the originating Cisco IOS gateway cut through the voice path, as if it received an alert with a PI of 8 from the PSTN.
• The gateway can also provide a ringback tone on the IP call leg if necessary. The tone ringback alert-no-pi command enables this functionality, and must be used only if the PSTN switch cannot provide inband ringback tone.