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🔗 Telecommunications 🔗 Radio

Comfort noise (or comfort tone) is synthetic background noise used in radio and wireless communications to fill the artificial silence in a transmission resulting from voice activity detection or from the audio clarity of modern digital lines.

Some modern telephone systems (such as wireless and VoIP) use voice activity detection (VAD), a form of squelching where low volume levels are ignored by the transmitting device. In digital audio transmissions, this saves bandwidth of the communications channel by transmitting nothing when the source volume is under a certain threshold, leaving only louder sounds (such as the speaker's voice) to be sent. However, improvements in background noise reduction technologies can occasionally result in the complete removal of all noise. Although maximizing call quality is of primary importance, exhaustive removal of noise may not properly simulate the typical behavior of terminals on the PSTN system.

The result of receiving total silence, especially for a prolonged period, has a number of unwanted effects on the listener, including the following:

• the listener may believe that the transmission has been lost, and therefore hang up prematurely.
• the speech may sound "choppy" (see noise gate) and difficult to understand.
• the sudden change in sound level can be jarring to the listener.

To counteract these effects, comfort noise is added, usually on the receiving end in wireless or VoIP systems, to fill in the silent portions of transmissions with artificial noise. The noise generated is at a low but audible volume level, and can vary based on the average volume level of received signals to minimize jarring transitions.

In many VoIP products, users may control how VAD and comfort noise are configured, or disable the feature entirely.

As part of the RTP audio video profile, RFC 3389 defines a standard for distributing comfort noise information in VoIP systems.

A similar concept is that of sidetone, the effect of sound that is picked up by a telephone's mouthpiece and introduced (at low level) into the earpiece of the same handset, acting as feedback.

During the siege of Leningrad, the beat of a metronome was used as comfort noise on the Leningrad radio network, indicating that the network was still functioning.

Many radio stations broadcast birdsong, city-traffic or other atmospheric comfort noise during periods of deliberate silence. For example, in the UK, silence is observed on Remembrance Sunday, and London's quiet city ambiance is used. This is to reassure the listener that the station is on-air, but primarily to prevent silence detection systems at transmitters from automatically starting backup tapes of music (designed to be broadcast in the case of transmission link failure).

🔗 Computing 🔗 Telecommunications

Gemini space denotes the whole of the public information that is published on the Internet by the Gemini community via the Gemini protocol. Thus, Gemini spans an alternative communication web, with hypertext documents that include hyperlinks to other resources that the user can easily access, similar to the secure version of the Hypertext Transfer Protocol (HTTPS), but with a focus on simplified information sharing, both in respect to creation and reading of Gemini content.

🔗 Telecommunications 🔗 Astronomy 🔗 Weather 🔗 Astronomy/Solar System 🔗 Weather/Weather 🔗 Weather/Space weather

The Carrington Event was the most intense geomagnetic storm in recorded history, peaking from 1–2 September 1859 during solar cycle 10. It created strong auroral displays that were reported globally and caused sparking and even fires in multiple telegraph stations. The geomagnetic storm was most likely the result of a coronal mass ejection (CME) from the Sun colliding with Earth's magnetosphere.

The geomagnetic storm was associated with a very bright solar flare on 1 September 1859. It was observed and recorded independently by British astronomers Richard Christopher Carrington and Richard Hodgson—the first records of a solar flare.

A geomagnetic storm of this magnitude occurring today would cause widespread electrical disruptions, blackouts, and damage due to extended outages of the electrical power grid.

🔗 Telecommunications

The Wheatstone system was an automated telegraph system that replaced a human operator with machines capable of sending and recording Morse code at a consistent fast rate. The system included a perforator, which prepared punched paper tape called a Wheatstone slip, a transmitter that read the tape and converted the symbols into dots and dashes encoded as mark and space electric currents on the telegraph line, and a receiver at the other end of the telegraph line that printed the Morse symbols. The system was invented by Charles Wheatstone. Enhancements could be made so that it was a duplex system, able to send and receive on the same line simultaneously.

The Wheatstone slip was a paper tape that contained holes in a pattern to control the mark and space signals on the telegraph line. The paper tape was from 0.46 to 0.48 inches in width, (but the standard width is from 0.472 to 0.475 inches) and a standard thickness of 0.004 to 0.0045 inches. Olive oil coating lubricated the punch process. There were three rows of holes. The middle row forms a rack so that a star wheel can move the paper forward. Every used position on the tape has a middle hole punched. The top hole indicates when to turn on the mark signal on the line, and the bottom hole says to turn off the mark signal. Each vertical column represents a time interval in the Morse code, including the spacing between the holes. The holes are spaced 0.1 inches apart. A column of three holes turns on the mark at the beginning of the interval, and turns it off at the end making a dot. If there is a top hole without a bottom, and then the next column has a bottom without a top hole, mark is on for three intervals, and a dash is represented. If there is only a centre hole, then nothing changes, and this would normally be used to put in space between letters and words.

The Wheatstone perforator was a manually operated hole punch machine to produce Wheatstone slips. It had three buttons (or keys) labelled "A", "A1" and "A2". "A" punched the pattern for dot, "A1" punched the pattern for space, and "A2" punched the dash pattern in two columns. The keys were so difficult to press that fist-held rubber-tipped mallets were used to depress them and operate the punches. Using this, invalid combinations of holes could not be produced. The blank paper tape was fed in from the right over a roller and came out the left side. It was oriented in a vertical plane. The paper punches were labelled with numbers: 1 for the top hole of the dot, 2 for the sprocket hole for dot, and 3 for the bottom hole for dot. When a dash was punched, extra hole punches to the right punched a centre hole with number 4 and a bottom hole with number 5. The perforator was introduced in 1867. It enabled transmission speeds on a telegraph line to increase to 70 words per minute. The very first message ever punched onto a tape was "SOS EIOS". The manual perforator was subsequently replaced by keyboard perforators like the Gell keyboard perforator or Kleinschmidt keyboard perforator.

Each of the keys had a spring to restore its position after pressing. Each key moved a corresponding lever underneath the instrument. The other end of the levers protruded up into the back of the mechanism. Each punch rod also had a spring to put it back in place after punching a hole. For space and dot keying (A or A1) the star wheel was only allowed to turn one position by a pawl, and the paper tape only moved forward one position. However, when key A2 was hit, the corresponding lever B2 raised a bar (h) which allowed another lever attached to the pawl to move further back when the star wheel rotated, and the wheel could turn two positions, for a dash. The distance the paper tape moved for each position was determined by how far lever k moved, and its range of movement had to be set by adjusting screws i and t. A flat spring g stored energy from the punch to move the paper. The force of the spring was determined by adjusting screws n and n'. A guide roller (r) with a groove was pressed by an adjustable spring to press the pawl against the star wheel. The star wheel was on a frame with a piece sticking out the left hand side as a lever. When the operator wanted to insert paper tape, this lever was pulled, and the star wheel retracted from the paper.

The Wheatstone transmitter read a paper tape (Wheatstone slip) and converted the dot pattern into mark and space symbols on the telegraph line. It worked by two rods alternately rising up to sample the holes in the tape. First of all the top hole was probed, and if the rod could go through, it moved a compound lever that connected the mark signal to the line. With no hole the lever remained unmoved. Next the top hole rod dropped and the bottom hole rod checked whether there was a bottom hole in the tape. If there was, the compound lever was moved back to connect the space signal on the line. If there was no hole, the compound lever was left alone as it was. An extra switch enabled the transmitter to be bypassed so that a Morse key could be used instead.

The Wheatstone receiver converted the signal on the telegraph line to an inked pattern on a paper strip. An electromagnet electrically connected to the telegraph line moved an inking wheel to press against the paper. A clockwork mechanism advanced the paper tape, and turned the inking wheel, and an ink supply wheel. The paper advance speed could be adjusted between 7 and 60 feet per minute. Power to the clockwork had three sources: it could be a coiled spring, a weight, or an electric motor. Paper spools were stored in drawers beneath the reader to allow quick change when one was exhausted. The ink supply wheel turned in an inkwell. The machine was started and stopped by use of a lever. In electrical characteristics, the electromagnet had two windings, each of 100 ohms resistance. These could be connected in parallel or series to achieve a 50 or 200 ohm resistance, to better match the telegraph line. Other maintenance that might have been required was cleaning of the marker and supply wheels, adjusting the armature-coil spacing to avoid a marking or spacing bias, and cleaning the sounding tongue and contact points.

The Wheatstone telegram consisted of strips of paper tape with the Morse code printed on it, pasted on a form. The telegram would later be retyped to make a final presentable message for the recipient.

🔗 Telecommunications 🔗 Law Enforcement

Phone cloning is the copying of identity from one cellular device to another.

🔗 Telecommunications

A payphone (alternative spelling: pay phone) is typically a coin-operated public telephone, often located in a telephone booth or in high-traffic outdoor areas, with pre-payment by inserting money (usually coins) or by billing a credit or debit card, or a telephone card. Prepaid calling cards also facilitate establishing a call by first calling the provided toll-free telephone number, entering the card account number and PIN, then the desired telephone number. An equipment usage fee may be charged as additional units, minutes or tariff fee to the collect/third-party, debit, credit, telephone or prepaid calling card when used at payphones. By agreement with the landlord, either the phone company pays rent for the location and keeps the revenue, or the landlord pays rent for the phone and shares the revenue.

Payphones are often found in public places to contribute to the notion of universal access to basic communication services. One thesis, written as early as 2003, recognised this as a digital divide problem.

In the 20th century, payphones in some countries, such as Spain, used token coins, available for sale at a local retailer, to activate pay phones, instead of legal tender coins. In some cases, these were upgraded to use magnetic cards or credit card readers over the years.

In the past, payphones were ubiquitous worldwide, but their prevalence has decreased significantly over the years due to the increasing availability of mobile phones, even though cell phone service is not always available in emergencies.

🔗 Telecommunications

Through-the-Earth (TTE) signalling is a type of radio signalling used in mines and caves that uses low-frequency waves to penetrate dirt and rock, which are opaque to higher-frequency conventional radio signals.

In mining, these lower-frequency signals can be relayed underground through various antennas, repeater or mesh configurations, but communication is restricted to line of sight to these antenna and repeaters systems.

🔗 Technology 🔗 Telecommunications

A mobile phone, cellular phone, cell phone, cellphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone that can make and receive calls over a radio frequency link while the user is moving within a telephone service area. The radio frequency link establishes a connection to the switching systems of a mobile phone operator, which provides access to the public switched telephone network (PSTN). Modern mobile telephone services use a cellular network architecture, and, therefore, mobile telephones are called cellular telephones or cell phones, in North America. In addition to telephony, 2000s-era mobile phones support a variety of other services, such as text messaging, MMS, email, Internet access, short-range wireless communications (infrared, Bluetooth), business applications, video games, and digital photography. Mobile phones offering only those capabilities are known as feature phones; mobile phones which offer greatly advanced computing capabilities are referred to as smartphones.

The development of metal-oxide-semiconductor (MOS) large-scale integration (LSI) technology, information theory and cellular networking led to the development of affordable mobile communications. The first handheld mobile phone was demonstrated by John F. Mitchell and Martin Cooper of Motorola in 1973, using a handset weighing c. 2 kilograms (4.4 lbs). In 1979, Nippon Telegraph and Telephone (NTT) launched the world's first cellular network in Japan. In 1983, the DynaTAC 8000x was the first commercially available handheld mobile phone. From 1983 to 2014, worldwide mobile phone subscriptions grew to over seven billion—enough to provide one for every person on Earth. In the first quarter of 2016, the top smartphone developers worldwide were Samsung, Apple, and Huawei, and smartphone sales represented 78 percent of total mobile phone sales. For feature phones (slang: “dumbphones”) as of 2016, the largest were Samsung, Nokia, and Alcatel.

🔗 United States/U.S. Government 🔗 United States 🔗 Mass surveillance 🔗 Telecommunications

The Communications Assistance for Law Enforcement Act (CALEA), also known as the "Digital Telephony Act," is a United States wiretapping law passed in 1994, during the presidency of Bill Clinton (Pub. L. No. 103-414, 108 Stat. 4279, codified at 47 USC 1001-1010).

CALEA's purpose is to enhance the ability of law enforcement agencies to conduct lawful interception of communication by requiring that telecommunications carriers and manufacturers of telecommunications equipment modify and design their equipment, facilities, and services to ensure that they have built-in capabilities for targeted surveillance, allowing federal agencies to selectively wiretap any telephone traffic; it has since been extended to cover broadband Internet and VoIP traffic. Some government agencies argue that it covers mass surveillance of communications rather than just tapping specific lines and that not all CALEA-based access requires a warrant.

The original reason for adopting CALEA was the Federal Bureau of Investigation's worry that increasing use of digital telephone exchange switches would make tapping phones at the phone company's central office harder and slower to execute, or in some cases impossible. Since the original requirement to add CALEA-compliant interfaces required phone companies to modify or replace hardware and software in their systems, U.S. Congress included funding for a limited time period to cover such network upgrades. CALEA was passed into law on October 25, 1994 and came into force on January 1, 1995.

In the years since CALEA was passed it has been greatly expanded to include all VoIP and broadband Internet traffic. From 2004 to 2007 there was a 62 percent growth in the number of wiretaps performed under CALEA – and more than 3,000 percent growth in interception of Internet data such as email.

By 2007, the FBI had spent $39 million on its Digital Collection System Network (DCSNet) system, which collects, stores, indexes, and analyzes communications data.

🔗 Telecommunications

Digital mobile radio (DMR) is a limited open digital mobile radio standard defined in the European Telecommunications Standards Institute (ETSI) Standard TS 102 361 parts 1–4 and used in commercial products around the world. DMR, along with P25 phase II and NXDN are the main competitor technologies in achieving 6.25 kHz equivalent bandwidth using the proprietary AMBE+2 vocoder. DMR and P25 II both use two-slot TDMA in a 12.5 kHz channel, while NXDN uses discrete 6.25 kHz channels using frequency division and TETRA uses a four-slot TDMA in a 25 kHz channel.

DMR was designed with three tiers. DMR tiers I and II (conventional) were first published in 2005, and DMR III (Trunked version) was published in 2012, with manufacturers producing products within a few years of each publication.

The primary goal of the standard is to specify a digital system with low complexity, low cost and interoperability across brands, so radio communications purchasers are not locked into a proprietary solution. In practice, given the current limited scope of the DMR standard, many vendors have introduced proprietary features that make their product offerings non-interoperable with other brands.