Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with broadcast television, in which the television signal is transmitted over-the-air by radio waves and received by a television antenna attached to the television; or satellite television, in which the television signal is transmitted over-the-air by radio waves from a communications satellite orbiting the Earth, and received by a satellite dish antenna on the roof. FM radio programming, high-speed Internet, telephone services, and similar non-television services may also be provided through these cables. Analog television was standard in the 20th century, but since the 2000s, cable systems have been upgraded to digital cable operation.
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. The carrier is higher in frequency than the modulation signal. The purpose of modulation is to impress the information on the carrier wave, which is used to carry the information to another location. In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver. Another purpose is to transmit multiple channels of information through a single communication medium, using frequency division multiplexing (FDM). For example in cable television which uses FDM, many carrier signals, each modulated with a different television channel, are transported through a single cable to customers. Since each carrier occupies a different frequency, the channels do not interfere with each other. At the destination end, the carrier signal is demodulated to extract the information bearing modulation signal.
In computing, booting is the process of starting a computer as initiated via hardware such as a button or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its main memory, so some process must load software into memory before it can be executed. This may be done by hardware or firmware in the CPU, or by a separate processor in the computer system.
In telecommunications and computer networking, multiplexing is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource. For example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now widely applied in communications. In telephony, George Owen Squier is credited with the development of telephone carrier multiplexing in 1910.
Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibers, wireless communication using radio spectrum, storage media and computer buses. The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal.
The Automatic Voice Network was a worldwide American military telephone system. The system was built starting in 1963, based on the Army's existing Switch Communications Automated Network (SCAN) system.
The North American Numbering Plan (NANP) is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the international calling code 1. Some North American countries, most notably Mexico, do not participate in the NANP.
A cellular network or mobile network is a communication network where the link to and from end nodes is wireless. The network is distributed over land areas called "cells", each served by at least one fixed-location transceiver. These base stations provide the cell with the network coverage which can be used for transmission of voice, data, and other types of content. A cell typically uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed service quality within each cell.
Area codes 213 and 323 are telephone area codes in the North American Numbering Plan (NANP) for the state of California. They are assigned to a numbering plan area (NPA) that comprises, roughly, the area of central Los Angeles, and includes several Southeast LA communities, such as Bell and Huntington Park. The area codes designated separate NPAs starting in 1998, when 323 was added, but were combined in an overlay plan into a single NPA in 2017. Previously, just downtown Los Angeles and immediately adjoining neighborhoods were served by area code 213, and the rest of central Los Angeles used area 323. Area code 213 is one of the original area codes created with the NANP in 1947, and was split five times over the decades.
In telecommunications, an overlay plan is a telephone numbering plan that assigns multiple area codes to a geographic numbering plan area (NPA). Overlaying numbering plan area codes is practiced in territories of the North American Numbering Plan (NANP) to prevent exhaustion of telephone numbers and central office codes in growth areas.
In telecommunications, an area code split is the practice of introducing a new telephone area code by geographically dividing an existing numbering plan area (NPA), and assigning area codes to the resulting divisions, but retaining the existing area code only for one of the divisions. The purpose of this practice is to provide more central office prefixes, and therefore more telephone numbers, in an area with high demand for telephone services, and prevent a shortage of telephone numbers.
A telephone exchange name or central office name was a distinguishing and memorable name assigned to a central office. It identified the switching system to which a telephone was connected. Each central office served a maximum of 10,000 subscriber lines identified by the last four digits of the telephone number. Areas or cities with more subscribers were served by multiple central offices, possibly hosted in the same building. The leading letters of a central office name were used as the leading components of the telephone number representation, so that each telephone number in an area was unique. These letters were mapped to digits, which was indicated visibly on a dial telephone.
A digital subscriber line (DSL) modem is a device used to connect a computer or router to a telephone line which provides the digital subscriber line (DSL) service for connection to the Internet, which is often called DSL broadband. The modem connects to a single computer or router, through an Ethernet port, USB port, or is installed in a computer PCI slot.
Area codes 408 and 669 are telephone area codes in the North American Numbering Plan (NANP) in the U.S. state of California. The numbering plan area comprises most of Santa Clara County and Northern Santa Cruz County, and includes Gilroy, Morgan Hill, Saratoga, Los Gatos, Monte Sereno, Milpitas, Sunnyvale, Santa Clara, Cupertino, Campbell, and San Jose.
Area code 707 is a telephone area code in the North American Numbering Plan (NANP) for the northwestern part of the U.S. state of California. It was created by a split of area code 415 on March 1, 1959. It serves part of the northern San Francisco Bay Area, as well as the North Coast. Major cities in the area code include Napa, Sebastopol, Vallejo, Benicia, Fairfield, Santa Rosa, Windsor, Healdsburg, Rohnert Park, Petaluma, Fort Bragg, Rio Vista, Crescent City, Eureka, Clearlake, Vacaville, Dixon, and Ukiah.
Area codes 410, 443, and 667 are telephone area codes serving the eastern half of the U.S. state of Maryland, including the Baltimore metropolitan area and the Eastern Shore. The 410 area code is the original area code, while the 443 and 667 codes are overlay codes. 443 and 667 were primarily used with cellular phones and competitive local exchange carriers such as Comcast or Cavalier Telephone when introduced but have since become universal in their carrier availability.
020 is the national dialling code for London in the United Kingdom. All subscriber numbers within the area code consist of eight digits and it has capacity for approaching 100 million telephone numbers. The code is used at 170 telephone exchanges in and around Greater London as part of the largest linked numbering scheme in the United Kingdom. In common with all other British area codes the initial '0' is a trunk prefix that is not required when dialling London from abroad.
The original North American area codes were established by the American Telephone & Telegraph Company (AT&T) in the immediate post-WWII period. Creating a comprehensive and universal, continent-wide telephone numbering plan was a basic requirement for nationwide Operator Toll Dialing which had the goal of speeding the connecting times for long-distance calling by eliminating intermediary telephone operators. It had the eventual benefit of direct distance dialing (DDD) by telephone subscribers. It established a uniform destination addressing and call routing system for all telephone networks in North America that had become an essential public service.
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that feasible with the human voice, but with a similar scale of expediency; thus, slow systems are excluded from the field.
Operator Toll Dialing was a telephone call routing and toll-switching system for the Bell System and the independent telephone companies in the United States and Canada that was developed in the 1940s. It automated the switching and billing of long-distance calls. The concept and technology evolved from the General Toll Switching Plan of 1929, and gained technical merits by the cutover of a new type of crossbar switching system in Philadelphia to commercial service in August 1943. This was the first system of its kind for automated forwarding of calls between toll switching centers, but it served customers only for regional toll traffic. It established initial experience with automatic toll switching for the design of a nationwide effort that was sometimes referred to as Nationwide Operator Toll Dialing.
