A General Statistical Determination of Transmission Characteristics Applied to L Multiplex

The demand for new services offered by the Bell System is increasing rapidly. Many of the services have performance requirements that are more critical than those of voice message telephone. They include data services over voice-band private lines and several types of DATAP H O N E service over the switched network, and wideband data services over groups (48-kc wide) and supergroups (2-40-kc wide) provided by L-multiplexed carrier facilities of the L-carrier plant. Services covering even wider bandwidths are under development. They are more critical in that they tolerate considerably less impairment from a number of sources. Two such impairments are amplitude and envelope delay 1031 1032 T H E B E L L SYSTEM TECHNICAL J O U R N A L , J U L Y - A U G . 19(55 distortion that are present in the L-type terminals which provide our long-haul facilities. Equalization of the terminals carrying these services seems the obvious solution for reducing distortion to tolerable limits. Equalization in the frequency domain is the process of designing networks which introduce distortions of equal magnitude but in the opposite sense to those of the system characteristic to be equalized. The success of such equalization hinges critically on the precise statistical knowledge of existing characteristics actually encountered in the plant and is limited by their variability. Data acquision on transmission of a network as vast and complex as the L carrier plant can be accomplished only by having a judiciously chosen sampling plan.