Number 1 Electronic Switching System

Number 1 Electronic Switching System. The Number 1 Electronic Switching System (1ESS) was the first large-scale, stored-program control telephone exchange deployed in the Bell System network. Developed by Bell Labs and manufactured by Western Electric, it represented a revolutionary leap from electromechanical systems like the Number 5 Crossbar to fully electronic, computer-controlled switching. Its initial installation in Succasunna, New Jersey in 1965 marked the beginning of the digital era in telecommunications, providing unprecedented reliability, capacity, and the foundation for new customer features.

Overview

The system was a monumental achievement in telephone exchange engineering, designed to handle the immense call volume of the North American Numbering Plan. It served as a central office switch for both local and toll switching, forming the backbone of the AT&T long-distance network. The deployment of the 1ESS was a critical step in modernizing the Bell System's infrastructure, moving away from relay-based and crossbar switch technologies. Its introduction coincided with major projects like the Project Mercury communications network and supported the growing demand forecast by the National Security Agency and other federal agencies.

Development and deployment

Development began in the late 1950s under the direction of engineers at Bell Labs in Murray Hill, New Jersey. Key figures included A.J. "Jack" Busch and teams that had previously worked on systems like the Electronic Switching System (ESS) prototype. The first commercial office was cut over in Succasunna, New Jersey on May 30, 1965, succeeding a Step-by-Step switching system. Subsequent deployments rapidly followed in major cities like Philadelphia, Chicago, and Los Angeles, often replacing older panel switch offices. The rollout was a massive undertaking by Western Electric, requiring extensive training for Bell System personnel and coordination with the Federal Communications Commission.

System architecture

At its core, the 1ESS utilized a duplexed central control based on the IBM 7090 computer design, built from discrete transistors and ferrite core memory. This stored program control architecture executed instructions from a permanent read-only memory woven with magnetic wires. The switching fabric itself was not fully electronic; it employed sophisticated ferreed switches—a hybrid of ferrite cores and sealed reed relay contacts—to connect voice paths. This design separated the control logic from the speech network, a principle later refined in the Number 4 Electronic Switching System. Critical subsystems included the Scannifier and Distributor for monitoring lines and initiating actions, with overall reliability ensured through the Bell System's rigorous standards.

Features and capabilities

The system introduced a suite of advanced features previously impossible with electromechanical switches. These included Speed Calling, Call forwarding, and Three-way calling, which were programmable for individual subscribers. It provided superior traffic handling capacity and diagnostic capabilities, allowing remote maintenance from a Bell Labs-designed Teletypewriter terminal. The 1ESS also supported Touch-Tone dialing, Direct Distance Dialing, and complex routing for interstate calls. Its architecture allowed for software updates to add features, influencing later systems like the Northern Telecom DMS-100 and the ITT System 12.

Impact and legacy

The deployment of the 1ESS fundamentally transformed the public switched telephone network, setting a new standard for reliability that exceeded 99.999% uptime. It proved the viability of stored program control for large-scale telephony, directly paving the way for its successor, the 1A ESS, and digital switches like the 4ESS and 5ESS. The technology and expertise developed for the project influenced global telecommunications, seen in systems like the Nippon Telegraph and Telephone D10 and British Post Office System X. While largely retired by the 1990s in favor of digital exchanges, the 1ESS remains a landmark engineering achievement that bridged the electromechanical and digital ages, cementing the legacy of Bell Labs and the Bell System.

Category:Telephone exchanges Category:Bell Labs Category:History of telecommunications Category:American inventions