Electronic switching system

Electronic switching system
Name	Electronic switching system
Industry	Telecommunications
Predecessor	Electromechanical telephone exchange
Successor	Digital switching system
Related	Stored program control, Time-division multiplexing

Electronic switching system. An electronic switching system (ESS) is a telephone exchange that employs solid-state electronics and computerized control to establish, maintain, and terminate connections within a telephone network. These systems replaced earlier electromechanical switching technologies, offering vastly greater speed, reliability, and capacity for new services. The core innovation was the application of stored program control (SPC), where a central computer directs all switching operations, fundamentally transforming network architecture and capabilities.

Overview

The primary function of an electronic switching system is to automate the routing of voice and data calls through a complex telecommunications infrastructure. Unlike their predecessors that used physical switches like crossbar or Strowger mechanisms, ESS units utilize semiconductor components such as transistors and integrated circuits for logic and control. This shift enabled the introduction of sophisticated features including speed dialing, call forwarding, and conference calls. The deployment of these systems by entities like AT&T Corporation and various Regional Bell Operating Companies was a critical step toward fully digital networks.

History and development

The conceptual groundwork for electronic switching was laid in the 1930s by researchers like Alec Reeves, who pioneered pulse-code modulation. Significant development began in the post-World War II era, with Bell Labs initiating the ESSEX project in the 1950s to explore stored program control. The first large-scale commercial deployment was Bell System's 1ESS switch, which began service in Succasunna, New Jersey in 1965. International development proceeded in parallel, with systems like the AXE telephone exchange from Ericsson in Sweden and the DMS-100 from Northern Telecom in Canada. These efforts were often supported by national PTT authorities.

System architecture

A classic electronic switching system architecture is built around a central control complex, typically a duplexed computer for reliability, executing a stored program control software suite. This control interfaces with a switching network, which in early systems used ferreed or reed relay crosspoints, and later incorporated time-division multiplexing (TDM) buses. Critical peripherals include scanning equipment to detect line status, signal distributors to activate switches, and magnetic core memory or later semiconductor memory for storing call data and translation information. This modular design separated call processing logic from the physical switching matrix.

Types and technologies

Electronic switching systems evolved through several technological generations. Early space-division systems, like the 1ESS switch and 2ESS switch, used electronic control to operate metallic crosspoint matrices. The subsequent adoption of pulse-code modulation led to time-division digital switches, such as the 4ESS switch for toll offices and the 5ESS Switch for local exchanges. Other notable types include the 1A ESS for large metropolitan areas and the NEAX series from NEC Corporation. While largely electronic, many hybrid systems retained some electromechanical components in peripheral units.

Applications and deployment

Electronic switching systems were deployed across all tiers of the public switched telephone network. Local exchange carriers used models like the 5ESS Switch or GTE's GTD-5 EAX to serve residential and business subscribers. For long-distance connections, AT&T Long Lines utilized the high-capacity 4ESS switch in its toll centers. Internationally, systems like the System X in the United Kingdom and the EWSD from Siemens AG were installed by Deutsche Bundespost and other operators. Their reliability also made them suitable for critical government and military communications networks.

Impact and legacy

The introduction of electronic switching systems catalyzed a revolution in telecommunications, dramatically improving network efficiency and enabling a suite of custom calling features that became standard. It provided the essential infrastructure for future digital services like Integrated Services Digital Network (ISDN). The technology's success directly led to the development of fully digital switching systems and influenced the architecture of early data networking equipment. While now largely superseded by Voice over IP and softswitch technologies, the principles of stored program control remain foundational to modern network engineering.

Category:Telecommunications equipment Category:Telephone exchanges Category:American inventions