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SP-1 (Stored Program 1) was the name of a computerized telephone exchange (a so-called switching office) manufactured by Northern Electric (later Northern Telecom and now Nortel Networks beginning in 1972) in Canada. It was introduced in 1971 (as stated in a Northern Telecom print ad that is included (page 55) in a history of Nortel, written by Peter C. Newman who was commissioned by Nortel to write it. Copyright is 1995. No ISBN.)
A telephone exchange is a telecommunications system used in the public switched telephone network or in large enterprises. An exchange consists of electronic components and in older systems also human operators that interconnect (switch) telephone subscriber lines or virtual circuits of digital systems to establish telephone calls between subscribers.
Canada is a country in the northern part of North America. Its ten provinces and three territories extend from the Atlantic to the Pacific and northward into the Arctic Ocean, covering 9.98 million square kilometres, making it the world's second-largest country by total area. Canada's southern border with the United States is the world's longest bi-national land border. Its capital is Ottawa, and its three largest metropolitan areas are Toronto, Montreal, and Vancouver. As a whole, Canada is sparsely populated, the majority of its land area being dominated by forest and tundra. Consequently, its population is highly urbanized, with over 80 percent of its inhabitants concentrated in large and medium-sized cities, many near the southern border. Canada's climate varies widely across its vast area, ranging from arctic weather in the north, to hot summers in the southern regions, with four distinct seasons.
As indicated by the name "Stored Program", the SP-1 introduced computer control to the telephone switching market. (AT&T's #1ESS preceded the SP-1 by several years.)
A central computer controlled the operation of the switch. Switch behavior was determined by the operation of a computer program.
With its use of computer hardware and software control, the SP-1 marked an evolutionary step in telephony design. It was an intermediate form between the previous generation of electromechanical systems and the next generation of fully digital systems. Like the previous generation of systems, the SP-1 was an analog switch that used a special form of mechanical relay (Minibar crossbar switch) to provide the voice connections. The voice signal remained in the analog domain throughout the exchange, with the crossbar switches providing a metallic path to connect the end points of a call together. However the SP1 replaced the previous generation's complex relay-based controllers (markers) with a modern Harvard architecture electronic computer, with separate data and program memories. SSI DTL logic was used throughout. Two types of memory was used - ferrite sheet memory for the CPU and Piggyback Twistor memory for the storage of program and routing information. A number of variations on the base switch were available. A "two wire" version for local service, a four wire version for toll service. Two/four wire versions were also available as was a TOPS variant that was used to provide Operator services. The first four wire switch (four wire-tops, i.e., it provided toll switching and operator services) was placed in service in Thunder Bay circa 1972. The operator service consoles (CRTs) used an Intel 4004 processor.
In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two systems interact with each other. This process is especially prominent in systems such as those of DC Machines which can be designed and operated to generate power from a mechanical process (generator) or used to power a mechanical effect (motor). Electrical engineering in this context also encompasses electronics engineering.
In electronics, a crossbar switch is a collection of switches arranged in a matrix configuration. A crossbar switch has multiple input and output lines that form a crossed pattern of interconnecting lines between which a connection may be established by closing a switch located at each intersection, the elements of the matrix. Originally, a crossbar switch consisted literally of crossing metal bars that provided the input and output paths. Later implementations achieved the same switching topology in solid state semiconductor chips. The cross-point switch is one of the principal switch architectures, together with a rotary switch, memory switch, and a crossover switch.
A marker is a type of special purpose control system that was used in electromechanical telephone central office switches. Switches employing markers belong to a class of switches known as "common control", as the purpose of a marker is to control the closure of contacts in the switching fabric that connect a circuit between the calling party and the called party. This is in contrast to "direct control" switches, where the switching elements were controlled directly by the customer's dial, such as the Step by Step switch. The term marker came from its use to mark a path of links through the switching fabric. A marker's comprehensive view of the switching fabric allowed it to find and assemble a path from one terminal to another, if the links were available, unlike the earlier graded progressive systems in which a path might not be found.
The next generation of systems evolved from the SP1 design to replace the analog switch with a digital technology. SP-1 proved the feasibility of software-controlled systems for telephony. It set the stage for the introduction of fully digital systems with the development of the DMS (Digital Multiplex Systems) by Nortel in the 1970s. (Nortel's SL-1 (PBX) was Nortel's first fully digital switching system, and it was introduced in service in 1975.)
Digital Multiplex System (DMS) is the name shared among several different telephony product lines from Nortel Networks for wireline and wireless operators. Among them are the DMS-1 Rural/Urban digital loop carrier, DMS-10 telephone switch, the DMS SuperNode family of telephone switches, and the S/DMS optical transmission system.
