Indicates when in-band progress tones should be generated on inbound ISDN calls. Valid values are: AS-NEEDED, NEVER and ALWAYS.
When this parameter is set to AS-NEEDED, the gateway will generate in-band progress tones only when request by the remote end in the ISDN setup message.
When this parameter is set to ALWAYS the gateway will generate in-band progress on every call coming on the current ISDN group.
When set to NEVER, the gateway will never generate in-band progress tone.
This parameter is optional its default value is: AS-NEEDED.