Core Issue
This issue may occur when the terminating (called) system gives an in-band ISDN busy signal but is not detected by the originating (calling) system. This may also affect the ability to hear outside dialing messages, such as when an unlisted or wrong number is dialed.
Resolution
The originating phone may be IP or Plain Old Telephone Service (POTS) type. The voice call convert-discpi-to-prog command converts an ISDN progression message to an H323 Progress Indicator (PI) message, available in Cisco IOS software version 12.2(1) and later. In some scenarios, simply upgrading to Cisco IOS Software Release 12.2(1) or later solves the issue. Otherwise, issue the voice call convert-discpi-to-prog command in global configuration mode.
For more information, refer to Troubleshooting No Busy Tone and No Announcement Messages on ISDN-VoIP (H.323) Calls.
