No. 4 ESS: Digital Interface

Abstract

This article describes the hardware and maintenance software implementation used for the Digital Interface (DIF), a new transmission interface for the No. 4 ESS. The DIF replaces the Digroup Terminal (DT) and the Signal Processor 2 (SP2) used for terminating digital carrier trunks. It also provides a more economical transmission interface for the No. 4 ESS, enhances the use of the LT‐1 connector for terminating analog carrier facilities, and provides a standard peripheral/processor interface for maintenance. In conjunction with the DIF, a hierarchical modularly structured maintenance software system was introduced to support the new No. 4 ESS peripherals. Incorporated into this system were the mechanisms required to support the introduction of microcomputer‐based peripherals such as DIF.