Progress indicator forbidden in setup

Hello, could anybody can explain me why the progress indicator has been set to "forbidden" in the setup message? (H.225v4 §7.3.10)

when H.323 is used in VoIP trunking between 2 ISUP networks, the lack of this information has an impact on the selection of the called ISDN terminal (for exemple : if a fax and a telephone are behind a PABX and if BC=3.1kHz, without the progress indicator, fax terminal can pick up the call instead of the telephone)

Thank you. Laurent Posé France Telecom.

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