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SF Tone
In telephony, single-frequency signaling (SF) is line signaling in which dial pulses or supervisory signals are conveyed by a single voice-frequency tone in each direction. SF and similar systems were used in 20th-century carrier systems. An SF signaling unit converts DC signaling (usually, at least in long-distance circuits, E&M signaling) to a format (characterized by the presence or absence of a single voice-frequency tone), which is suitable for transmission over an AC path, ''e.g.'', a carrier system. The SF tone is present in the on-hook or idle state and absent during the seized state. In the seized state, dial pulses are conveyed by bursts of SF tone, corresponding to the interruptions in dc continuity created by a rotary dial or other DC dialing mechanism. The SF tone may occupy a small portion of the user data channel spectrum, ''e.g.,'' 1600 Hz or 2600 Hz (SF "in-band signaling)". There may be a notch filter at the precise SF frequency, either filtering t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SF Signal
''SF Signal'' was a science fiction blog and fanzine published from 2003 to 2016. The site was launched by John DeNardo and JP Frantz and focused on writings, events, and other topics focusing on the genres of science fiction, fantasy, and other related genres. It hosted three podcasts, one of which won the 2014 Hugo Award for Best Fancast. The site itself won two Hugo Awards for Best Fanzine, 2012 and 2013. History The website was launched in 2003 by John DeNardo and JP Frantz after they noticed a lack of blogs focusing on science fiction. They decided to launch a blog where they could discuss science fiction and related genre writings, events and ideas that were interesting to them. As the website's popularity grew, they began to incorporate more original content and hired additional staff members as well as brought in new contributors. ''SF Signal'' published three podcasts: ''SF Crossing the Gulf'', ''The Three Hoarsemen'', and ''The SF Signal Podcast''. In 2012 ''SF Signa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2600 Hz
A blue box is an electronic device that produces tones used to generate the in-band signaling tones formerly used within the North American long-distance telephone network to send line status and called number information over voice circuits. This allowed the user, referred to as a "phreaker", to surreptitiously place long-distance calls that would be billed to another number or dismissed entirely as an incomplete call. A number of similar "color boxes" were also created to control other aspects of the phone network. First developed in the 1960s and used by a small phreaker community, the introduction of low-cost microelectronics in the early 1970s greatly simplified these devices to the point where they could be constructed by anyone reasonably competent with a soldering iron or breadboard construction. Soon after, models of relatively low quality were being offered fully assembled, but these generally required tinkering on the part of the user to keep operational. An exceptio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
T-carrier
The T-carrier is a member of the series of carrier systems developed by AT&T Bell Laboratories for digital transmission of multiplexed telephone calls. The first version, the Transmission System 1 (T1), was introduced in 1962 in the Bell System, and could transmit up to 24 telephone calls simultaneously over a single transmission line of copper wire. Subsequent specifications carried multiples of the basic T1 (1.544 Mbit/s) data rates, such as T2 (6.312 Mbit/s) with 96 channels, T3 (44.736 Mbit/s) with 672 channels, and others. Although a ''T2'' was defined as part of AT&T's T-carrier system, which defined five levels, T1 through T5, only the T1 and T3 were commonly in use.1999 ad: On the left, in an aisle seat, a man who very much "filled" his airline seat while on the right side of the aisle is a height-challenged man whose shoe toes barely reach the floor Transmission System 1 The T-carrier is a hardware specification for carrying multiple time-division mul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signalling (telecommunication)
In telecommunication, signaling is the use of signals for controlling communications. This may constitute an information exchange concerning the establishment and control of a telecommunication circuit and the management of the network. Classification Signaling systems may be classified based on several principal characteristics. In-band and out-of-band signaling In the public switched telephone network (PSTN), in-band signaling is the exchange of call control information within the same physical channel, or within the same frequency band, that the telephone call itself is using. An example is dual-tone multi-frequency signaling (DTMF), which is used on most telephone lines to customer premises. Out-of-band signaling is telecommunication signaling on a dedicated channel separate from that used for the telephone call. Out-of-band signaling has been used since Signaling System No. 6 (SS6) was introduced in the 1970s, and also in Signalling System No. 7 (SS7) in 1980 which became ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Four-wire Circuit
In telecommunication, a four-wire circuit is a two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path. The four-wire circuit gets its name from the fact that is uses four conductors to create two complete electrical circuits, one for each direction. The two separate circuits (channels) allow full- duplex operation with low crosstalk. In telephony a four-wire circuit was historically used to transport and switch baseband audio signals in the phone company telephone exchange before the advent of digital modulation and the electronic switching system eliminated baseband audio from the telco plant except for the local loop. The local loop is a two-wire circuit for one reason only: to save copper. Using half the number of copper wire conductors per circuit means that the infrastructure cost for wiring each circuit is halved. Although a lower quality circuit, the local loop al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Cable
An electrical cable is an assembly of one or more wires running side by side or bundled, which is used to carry electric current. One or more electrical cables and their corresponding connectors may be formed into a ''cable assembly'', which is not necessarily suitable for connecting two devices but can be a partial product (e.g. to be soldered onto a printed circuit board with a connector mounted to the housing). Cable assemblies can also take the form of a cable tree or cable harness, used to connect many terminals together. Etymology The original meaning of ''cable'' in the electrical wiring sense was for submarine telegraph cables that were armoured with iron or steel wires. Early attempts to lay submarine cables without armouring failed because they were too easily damaged. The armouring in these early days (mid-19th century) was implemented in separate factories to the factories making the cable cores. These companies were specialists in manufacturing wire rope of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carrier Signal
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a much higher frequency than the input signal does. The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave (as in radio communication), or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing (as in a cable television system). The term originated in radio communication, where the carrier wave creates the waves which carry the information (modulation) through the air from the transmitter to the receiver. The term is also used for an unmodulated emission in the absence of any modulating signal. In music production, carrier signals can be controlled by a modulating signal to change the sound property of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Defense Data Network
The Defense Data Network (DDN) was a computer networking effort of the United States Department of Defense from 1983 through 1995. It was based on ARPANET technology. History As an experiment, from 1971 to 1977, the Worldwide Military Command and Control System (WWMCCS) purchased and operated an ARPANET-type system from BBN Technologies for the Prototype WWMCCS Intercomputer Network (PWIN). The experiments proved successful enough that it became the basis of the much larger WIN system. Six initial WIN sites in 1977 increased to 20 sites by 1981. In 1975, the Defense Communication Agency (DCA) took over operation of the ARPANET as it became an operational tool in addition to an ongoing research project. At that time, the Automatic Digital Network (AUTODIN), carried most of the Defense Department's message traffic. Starting in 1972, attempts had been made to introduce some packet switching into its planned replacement, AUTODIN II. AUTODIN II development proved unsatisfactory, howe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blue Box
A blue box is an electronic device that produces tones used to generate the in-band signaling tones formerly used within the North American long-distance telephone network to send line status and called number information over voice circuits. This allowed the user, referred to as a "phreaker", to surreptitiously place long-distance calls that would be billed to another number or dismissed entirely as an incomplete call. A number of similar "color boxes" were also created to control other aspects of the phone network. First developed in the 1960s and used by a small phreaker community, the introduction of low-cost microelectronics in the early 1970s greatly simplified these devices to the point where they could be constructed by anyone reasonably competent with a soldering iron or breadboard construction. Soon after, models of relatively low quality were being offered fully assembled, but these generally required tinkering on the part of the user to keep operational. An excepti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Falsing
In telecommunications, falsing is when a decoder assumes that it is detecting a valid input even though one is not present. This is also known as a false decode. This article will discuss analog circuits used before digital signal processing. Examples of decoder falsing include: * a telephone answering machine detecting dial pulses from a rotary dial as ringing voltage, with the result that the answering machine answers in response to dialing. * a two-way radio with an enabled CTCSS decoder turns on the receive audio for one or two syllables of a signal with a close-in-tone-frequency (but wrong) CTCSS tone. The person listening to the radio occasionally hears nonsense partial words from the receiver's speaker: "et"... "up"... * a ringy telephone circuit with SF single-frequency signaling and poor level discipline drops calls because it sees harmonic frequencies or the distorted waveform as a valid "circuit idle" or "on-hook" SF signal. * power line transients cause a telemetry dec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telephone Call
A telephone call is a connection over a telephone network A telephone network is a telecommunications network that connects telephones, which allows telephone calls between two or more parties, as well as newer features such as fax and internet. The idea was revolutionized in the 1920s, as more and more ... between the called party and the calling party. First telephone call The first telephone call was made on March 10, 1876, by Alexander Graham Bell. Bell demonstrated his ability to "talk with electricity" by transmitting a call to his assistant, Thomas Watson. The first words transmitted were "Mr Watson, come here. I want to see you." This event has been called Bell's "greatest success", as it demonstrated the first successful use of the telephone. Although it was his greatest success, he refused to have a telephone in his own home because it was something he invented by mistake and saw it as a distraction from his main studies. Information transmission A telephone cal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Off-hook
In telephony, on-hook and off-hook are two states of a communication circuit. On subscriber telephones the states are produced by placing the handset onto or off the hookswitch. Placing the circuit into the off-hook state is also called ''seizing the line''. ''Off-hook'' originally referred to the condition that prevailed when telephones had a separate earpiece (''receiver''), which hung from its switchhook until the user initiated a telephone call by removing it. When off hook the weight of the receiver no longer depresses the spring-loaded switchhook, thereby connecting the instrument to the telephone line. Off-hook The term off-hook has the following meanings: * 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, such as tone or no tone and ground connection versus battery connection. Note that if ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
