This parameter indicates which ISDN message(s) shall be used to notify the remote end when the gateway generate in-band progress tones.

Valid values are: ALERTING, PROGRESS and BOTH.

When this parameter is set to ALERTING, the gateway will send only the ALERTING message.

When this parameter is set to PROGRESS the gateway will only send the PROGRESS message.

When this parameter is set to BOTH the gateway will send the PROGRESS message followed by the ALERTING message.

Of course the messages are containing the progress indicator information element.

This parameter is optional its default value is: PROGRESS.