usdFt1IfDataPolarity, now an obsolete object, selected the polarity of data transmitted on this fractional T1 interface, either normal(0) or inverted(1), with inverted used to guarantee sufficient one's density for clock recovery under certain line coding schemes. An admin would set this to inverted on links using coding that requires it to keep the remote end's timing recovery circuitry synchronized. For example, an admin might have set this to inverted(1) when configuring an FT1 circuit whose line coding did not otherwise ensure adequate density, to prevent loss of timing synchronization on the remote end.