The requirements in this addendum are intended to align the requirements in ANSI/TIA-464-C standard for Private Branch Exchange (PBX) systems with the new changes in ANSI/TIA-968-A and ANSI/TIA-968-A-1 standards mandated by FCC for Part 68 product registration. It also intended to assure satisfactory user voicegrade services in a high percentage of installations. If cases arise that have not been adequately addressed in this standard, any resulting problems should be resolved through the cooperation of the customer, the carrier, and the equipment supplier.

It is recognized that some PBX products may not be accommodated by this standard because of nonstandard line interfaces; e.g., proprietary digital station interfaces. In such systems, the station apparatus must be considered as a whole with the PBX and its associated station wiring, and the overall system must be described in terms of an acoustic (user) to an electrical (network) standard.