In order to provide telephone users with the most pleasing audio quality, proper control of echo and noise is necessary while maintaining the correct receiving volume.

The feature "T - Reference point " forms the basis for the Transmission and Loss Plan integration for the I.M. and U.S. markets. The Loss Plan is implemented on a country specific basis and is administered by AMO TREF

The 'T-reference point' is a defined interface between a PABX and the public ISDN network, at which pre-defined voice signal levels must be adhered to. In order to achieve a constant voice signal transmission quality, regardless of the connection type and network size, the T-reference point conditions also apply to analog interfaces, as well as to tones heard by subscribers. The attenuation values for the voice signal and tone levels are stored in the TREF table on the hard disk, and are loaded into the database with the TREF AMO