D2 channel bank: Per-channel equipment

Traditionally, the design of switching machines has assumed that the transmission plant consists of physical wire pairs. Therefore, appropriate interface equipment is necessary when a multiplex transmission system is substituted for wire pairs. This interface, or per-channel, equipment performs such functions as (i) 2-wire to 4-wire conversion to separate the two directions of transmission, (ii) detection of signaling and supervision information, and (iii) band-limiting and level compensation of the signal prior to sampling. Since failures of the multiplex system can cause massive service interruptions and tie up switching equipment, provision is made to detect such failures and alert the switching machine. Design of per-channel equipment is complicated by the number of options required to account for the large variety of ways in which switching machines utilize wire-pair plant. This article describes the per-channel equipment of the D2 Channel Bank and some of the considerations that went into its design.