This read-write TruthValue controls whether T.38 fax relay, the ITU real-time protocol for carrying fax over IP, is disabled on the media gateway. Admins toggle this because some networks or call agents cannot reliably support T.38 switch-over, and inhibiting it forces fax calls to fall back to a different transport. For example, if fax machines behind a gateway frequently fail mid-transmission when T.38 kicks in, an admin might set this to true to force fax calls through in a more stable mode instead.