A New Objective for Message Circuit Noise

For many years the Bell System over-all performance objective for message circuit noise has been as follows: "Noise from all sources in a subscriber-to-subscriber connection should seldom exceed 26 dbrnc* (20 dba) at the line terminals of the station set." Since its inception this objective has been a primary influence in the design of broadband transmission systems, and it has served as a guide for the engineering and maintenance of the message network. But improved and new services have gradually changed the makeup and the performance requirements of the plant. Thus, work was recently undertaken to establish a new performance objective -- one better suited to the noise conditions imposed by a changing communication network. The new objective provides a long-range Bell System goal and, as such, serves as a guide for the design of future systems and for establishing maintenance procedures. In addition, it indicates those areas where * T h e new unit for noise measurement with the 3 - t y p e noise measuring set is dbrnc. 1 Reference noise, " r n , " is 10~12 w a t t s of 1000-cps power, whereas " c " refers to C-message weighting. 719