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1AESS MCC
The Number One Electronic Switching System (1ESS) was the first large-scale stored program control (SPC) telephone exchange or electronic switching system in the Bell System
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Stored Program Control
Stored program control (SPC) was a telecommunications technology used for telephone exchanges controlled by a computer program stored in the memory of the switching system. SPC was the enabling technology of electronic switching systems (ESS) developed in the Bell System
Bell System
in the 1950s, and may be considered the third generation of switching technology. Stored program control was invented by Bell Labs
Bell Labs
scientist Erna Schneider Hoover
Erna Schneider Hoover
in 1954 who reasoned that computer software could control the connection of telephone calls.[1][2][3]Contents1 History 2 Types2.1 Centralized control2.1.1 Standby mode 2.1.2 Synchronous duplex mode 2.1.3 Load-sharing mode2.2 Distributed control3 See also 4 ReferencesHistory[edit] Proposed and developed in the 1950s, SPC was introduced in production electronic switching systems in the 1960s
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Loop Start
Loop start is a telecommunications supervisory protocol between a central office or private branch exchange (PBX) and a subscriber telephone for the purpose of starting and terminating a telephone call. It is the simplest of the telephone signaling systems, and uses the presence or absence of loop current to indicate the off-hook and on-hook loop states, respectively. It is used primarily for subscriber line signaling.Contents1 Protocol operation 2 Signaling extensions 3 See also 4 ReferencesProtocol operation[edit] When the telephone is on-hook, the potential of the ring conductor of the local loop is held at a nominal level of -48V DC with respect to the tip conductor, provided by the telephone exchange or a foreign exchange station (FXS) interface
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One-way Trunk
In telecommunication, a one-way trunk is a trunk between two switching centers, over which traffic may be originated from one preassigned location only. Note 1: The traffic may consist of two-way communications; the expression "one way" refers only to the origin of the demand for a connection. Note 2: At the originating end, the one-way trunk is known as an "outgoing trunk" ; at the other end, it is known as an "incoming trunk". References[edit]  This article incorporates public domain material from the General Services Administration
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On-hook
In telephony, the term on-hook has the following meanings:On hook telephone handsetThe condition that exists when a telephone or other user instrument is not in use, i.e., when idle waiting for a call. Note: on-hook originally referred to the storage of an idle telephone receiver, i.e., separate earpiece, on a switchhook. The weight of the receiver depresses the spring-loaded switchhook thereby disconnecting the idle instrument (except its bell) from the telephone line. One of two possible signaling states, such as tone or no tone, or ground connection versus battery connection. Note: if on-hook pertains to one state, off-hook pertains to the other. The idle state, i.e., an open loop of a subscriber line or PBX user loop. An operating state of a telecommunication circuit in which transmission is disabled and a high impedance, or "open circuit", is presented to the link by the end instrument(s)
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Off-hook
In telephony, the term off-hook has the following meanings:Off hook telephone.The condition that exists when a telephone or other user instrument is in use, i.e., during dialing or communicating. A general description of one of two possible signaling states at an interface between telecommunications systems,[1] such as tone or no tone and ground connection versus battery connection. Note that if off-hook pertains to one state, on-hook pertains to the other. The active state (i.e., a closed loop (short circuit between the wires) of a subscriber line or PBX user loop) An operating state of a communications link in which data transmission is enabled either for (a) voice or data communications or (b) network signaling.[2][3]On an ordinary two-wire telephone line, off-hook status is communicated to the telephone exchange by a resistance short across the pair
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Common Control
In telecommunication, a common control is an automatic telephone exchange arrangement in which the control equipment necessary for the establishment of connections is shared by being associated with a given call only during the period required to accomplish the control function for the given call. The first examples deployed on a major scale were the Director telephone system
Director telephone system
in London and the panel switch in the Bell System. Direct control telephone exchanges became rare in the 1960s, leaving only common control ones. Systems which have control subsystem as an integral part of the switching network itself were known as direct control switching systems. Systems in which the control subsytem is outside the switching network are known as Common control systems. Strowger exchanges are usually direct control systems, whereas crossbar, electronic exchanges including all stored program control systems are common control systems
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Traffic Service Position System
The Traffic Service Position System (TSPS) was developed by Bell Labs in Columbus, Ohio
Columbus, Ohio
to replace traditional cord switchboards
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E And M Signaling
E and M signaling
E and M signaling
is a type of supervisory line signaling that uses DC signals on separate leads, called the "E" lead and "M" lead, traditionally used in the telecommunications industry between telephone switches. Various mnemonic names have been used to memorize these letters, such as Ear and Mouth, the most common variation.8 Wires of E and M signaling
E and M signaling
(Type IV E&M)E&M was originally developed to allow PABXs in different geographic locations to communicate over an analog private circuit. Some digital interfaces such as Channel Associated Signaling also use versions of E&M signaling
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Magnetic Core Memory
Magnetic-core memory
Magnetic-core memory
was the predominant form of random-access computer memory for 20 years between about 1955 and 1975. Such memory is often just called core memory, or, informally, core. Core uses tiny magnetic toroids (rings), the cores, through which wires are threaded to write and read information. Each core represents one bit of information. The cores can be magnetized in two different ways (clockwise or counterclockwise) and the bit stored in a core is zero or one depending on that core's magnetization direction. The wires are arranged to allow for an individual core to be set to either a one or a zero and for its magnetization to be changed by sending appropriate electric current pulses through selected wires. The process of reading the core causes the core to be reset to a zero, thus erasing it. This is called destructive readout
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Saturation (magnetic)
Seen in some magnetic materials, saturation is the state reached when an increase in applied external magnetic field H cannot increase the magnetization of the material further, so the total magnetic flux density B more or less levels off. (It continues to increase very slowly due to the vacuum permeability.) Saturation is a characteristic of ferromagnetic and ferrimagnetic materials, such as iron, nickel, cobalt and their alloys.Contents1 Description 2 Explanation 3 Effects and uses 4 See also 5 ReferencesDescription[edit] Saturation is most clearly seen in the magnetization curve (also called BH curve or hysteresis curve) of a substance, as a bending to the right of the curve (see graph at right). As the H field increases, the B field approaches a maximum value asymptotically, the saturation level for the substance
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Line Signaling
Line signaling is a class of telecommunications signaling protocols. Line signaling is responsible for off-hook, ringing signal, answer, ground start, on-hook unidirectional supervision messaging in each direction from calling party to called party and vice versa. After an off-hook, line signaling initiates register signaling to accomplish the exchange of telephone numbers of called party and in more modern line-signaling protocols, the calling party as well. While register signaling occurs, line signaling remains quiescent unless the calling party goes on-hook or an abnormal cessation of the call occurs, such as due to equipment malfunction or shutdown or due to network outage upstream in that call-attempt's series of spanned trunks. Line signaling can be conveyed in a single DS0 channel of a trunk
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Dual-tone Multi-frequency
Dual-tone multi-frequency signaling
Dual-tone multi-frequency signaling
(DTMF) is an in-band telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed in the Bell System in the United States, and became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963.[1] DTMF is standardized as ITU-T Recommendation Q.23.[2] It is also known in the UK as MF4. The Touch-Tone system using a telephone keypad gradually replaced the use of rotary dial and has become the industry standard for landline and mobile service
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Ground Start
In telephony, ground start is a method of signaling from a terminal of a subscriber local loop to a telephone exchange, where one side of a cable pair is temporarily grounded to request dial tone. Most middle 20th-century American payphones used coin-first ground start lines, with the starting ground connection provided by the coin itself, bridging a set of contacts as it passes through the coin chute. Ground start trunk[edit] Telephone companies typically provide two types of dial tone switched circuits – ground start and loop start. Private branch exchanges (PBX) work best on ground start trunks because those trunks can give them an on hook signal allowing for timely clearing. Normal single line telephones and key systems typically work on loop start lines
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Histogram
A histogram is an accurate representation of the distribution of numerical data. It is an estimate of the probability distribution of a continuous variable (quantitative variable) and was first introduced by Karl Pearson.[1] It is a kind of bar graph. To construct a histogram, the first step is to "bin" the range of values—that is, divide the entire range of values into a series of intervals—and then count how many values fall into each interval. The bins are usually specified as consecutive, non-overlapping intervals of a variable. The bins (intervals) must be adjacent, and are often (but are not required to be) of equal size.[2] If the bins are of equal size, a rectangle is erected over the bin with height proportional to the frequency—the number of cases in each bin. A histogram may also be normalized to display "relative" frequencies
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Harvard Architecture
The Harvard architecture
Harvard architecture
is a computer architecture with physically separate storage and signal pathways for instructions and data. The term originated from the Harvard Mark I
Harvard Mark I
relay-based computer, which stored instructions on punched tape (24 bits wide) and data in electro-mechanical counters. These early machines had data storage entirely contained within the central processing unit, and provided no access to the instruction storage as data
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