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Level 10
Level 10

Core Issue

In some cases, Cisco IP phone users or Plain Old Telephone Service (POTS) users connected to a Cisco IOS® gateway may not hear a busy tone when they call a busy number on the Public Switched Telephone Network (PSTN). This is a problem when the PSTN disconnects the call with a normal call clearing cause code, instead of user busy. Instead of setting the cause code to user busy, the PSTN switch sets the progress indicator information element on the DISCONNECT message to eight, indicating that inband information is available. The disconnect message, however, causes the gateway and Cisco CallManager to release the call.


Issue the voice call convert-discpi-to-prog global configuration command, available in Cisco IOS Software Release 12.2(1). Doing this converts a DISCONNECT message with a progress indicator value of eight to a PROGRESS message with a progress indicator value of eight so that audio is cut through and the Cisco IP phone hears the disconnect tones or announcement from the PSTN. For further information, refer the document Troubleshooting No Busy Tone and No Announcement Messages on ISDN-VoIP (H.323) Calls. For more details on troubleshooting this and various other issues refer to The Cisco Press book Troubleshooting Cisco IP Telephony [ISBN 1-58705-075-7].

Problem Type

Call connection (Connection quality: One-way audio, no busy tone, dropped calls, etc.)

Call Connection

Dead air

Disconnect tone

Call connection establishment

Disconnection failure


Busy tone

When Problem Occurs

While call is connecting

End Where Problem is Heard or Device Type Involved

IP phone

Call Topology and Direction

IP network > PSTN/PBX/gateway

Q931 and H225 Call Setup Messages



Common Q931 Information Elements

8 - In-band information or an appropriate pattern is now available sent in alert

80 - Normal Disconnect

Progress Indicator Alteration

voice call convert-discpi-to-prog

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