Data transmission and data reception (or, more broadly, data communication or digital communications) is the transfer and reception of data (a digitalbitstream or a digitized analog signal^[1]) over a point-to-point or point-to-multipointcommunication channel. Examples of such channels are copper wires, optical fibers, wireless communication channels, storage media and computer buses. The data are represented as an electromagneticsignal, such as an electrical voltage, radiowave, microwave, or infrared signal.

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Analog or analogue transmission is a transmission method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable. The messages are either represented by a sequence of pulses by means of a line code (baseband transmission), or by a limited set of continuously varying waveforms (passband transmission), using a digital modulation method. The passband modulation and corresponding demodulation (also known as detection) is carried out by modem equipment. According to the most common definition of digital signal, both baseband and passband signals representing bit-streams are considered as digital transmission, while an alternative definition only considers the baseband signal as digital, and passband transmission of digital data as a form of digital-to-analog conversion.

Data transmitted may be digital messages originating from a data source, for example a computer or a keyboard. It may also be an analog signal such as a phone call or a video signal, digitized into a bit-stream, for example, using pulse-code modulation (PCM) or more advanced source coding (analog-to-digital conversion and data compression) schemes. This source coding and decoding is carried out by codec equipment.

Transmitted: 1 adj occurring among members of a family usually by heredity “genetically transmitted features” Synonyms: familial, genetic, hereditary, inherited, transmissible heritable, inheritable capable of being inherited. The data shows that when it comes to COVID-19, the locations where people contract the virus run the gamut. Most commonly, cases can be traced back to places where people spend a lot of time congregating together — such as your house or work — and crowded, indoor spaces like restaurants or gyms.

Distinction between related subjects[edit]

Courses and textbooks in the field of data transmission^[1] as well as digital transmission^[2][3] and digital communications^[4][5] have similar content.

Digital transmission or data transmission traditionally belongs to telecommunications and electrical engineering. Basic principles of data transmission may also be covered within the computer science or computer engineering topic of data communications, which also includes computer networking applications and networking protocols, for example routing, switching and inter-process communication. Although the Transmission Control Protocol (TCP) involves transmission, TCP and other transport layer protocols are covered in computer networking but not discussed in a textbook or course about data transmission.

The term tele transmission involves the analog as well as digital communication. In most textbooks, the term analog transmission only refers to the transmission of an analog message signal (without digitization) by means of an analog signal, either as a non-modulated baseband signal, or as a passband signal using an analog modulation method such as AM or FM. It may also include analog-over-analog pulse modulatated baseband signals such as pulse-width modulation. In a few books within the computer networking tradition, 'analog transmission' also refers to passband transmission of bit-streams using digital modulation methods such as FSK, PSK and ASK. Note that these methods are covered in textbooks named digital transmission or data transmission, for example.^[1]

The theoretical aspects of data transmission are covered by information theory and coding theory.

Protocol layers and sub-topics[edit]

Courses and textbooks in the field of data transmission typically deal with the following OSI model protocol layers and topics:

• Layer 1, the physical layer:
  • Channel coding including
    • Digital modulation schemes
    • Line coding schemes
    • Forward error correction (FEC) codes
• Layer 2, the data link layer:
  • Channel access schemes, media access control (MAC)
  • Packet mode communication and Frame synchronization
  • Error detection and automatic repeat request (ARQ)
• Layer 6, the presentation layer:
  • Source coding (digitization and data compression), and information theory.
  • Cryptography (may occur at any layer)

It is also common to deal with the cross-layer design of those three layers.^[6]

Applications and history[edit]

Data (mainly but not exclusively informational) has been sent via non-electronic (e.g. optical, acoustic, mechanical) means since the advent of communication. Analog signal data has been sent electronically since the advent of the telephone. However, the first data electromagnetic transmission applications in modern time were telegraphy (1809) and teletypewriters (1906), which are both digital signals. The fundamental theoretical work in data transmission and information theory by Harry Nyquist, Ralph Hartley, Claude Shannon and others during the early 20th century, was done with these applications in mind.

Data transmission is utilized in computers in computer buses and for communication with peripheral equipment via parallel ports and serial ports such as RS-232 (1969), FireWire (1995) and USB (1996). The principles of data transmission are also utilized in storage media for Error detection and correction since 1951.

Data transmission is utilized in computer networking equipment such as modems (1940), local area networks (LAN) adapters (1964), repeaters, repeater hubs, microwave links, wireless network access points (1997), etc.

In telephone networks, digital communication is utilized for transferring many phone calls over the same copper cable or fiber cable by means of pulse-code modulation (PCM), i.e. sampling and digitization, in combination with Time division multiplexing (TDM) (1962). Telephone exchanges have become digital and software controlled, facilitating many value added services. For example, the first AXE telephone exchange was presented in 1976. Since the late 1980s, digital communication to the end user has been possible using Integrated Services Digital Network (ISDN) services. Since the end of the 1990s, broadband access techniques such as ADSL, Cable modems, fiber-to-the-building (FTTB) and fiber-to-the-home (FTTH) have become widespread to small offices and homes. The current tendency is to replace traditional telecommunication services by packet mode communication such as IP telephony and IPTV.

Transmitting analog signals digitally allows for greater signal processing capability. The ability to process a communications signal means that errors caused by random processes can be detected and corrected. Digital signals can also be sampled instead of continuously monitored. The multiplexing of multiple digital signals is much simpler to the multiplexing of analog signals.

Because of all these advantages, and because recent advances in widebandcommunication channels and solid-state electronics have allowed scientists to fully realize these advantages, digital communications has grown quickly. Digital communications is quickly edging out analog communication because of the vast demand to transmit computer data and the ability of digital communications to do so.

The digital revolution has also resulted in many digital telecommunication applications where the principles of data transmission are applied. Examples are second-generation (1991) and later cellular telephony, video conferencing, digital TV (1998), digital radio (1999), telemetry, etc.

Data transmission, digital transmission or digital communications is the physical transfer of data (a digital bit stream or a digitized analog signal[1]) over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibers, wireless communication channels, storage media and computer buses. The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal.

While analog transmission is the transfer of a continuously varying analog signal over an analog channel, digital communications is the transfer of discrete messages over a digital or an analog channel. The messages are either represented by a sequence of pulses by means of a line code (baseband transmission), or by a limited set of continuously varying wave forms (passband transmission), using a digital modulation method. The passband modulation and corresponding demodulation (also known as detection) is carried out by modem equipment. According to the most common definition of digital signal, both baseband and passband signals representing bit-streams are considered as digital transmission, while an alternative definition only considers the baseband signal as digital, and passband transmission of digital data as a form of digital-to-analog conversion.

Data transmitted may be digital messages originating from a data source, for example a computer or a keyboard. It may also be an analog signal such as a phone call or a video signal, digitized into a bit-stream for example using pulse-code modulation (PCM) or more advanced source coding (analog-to-digital conversion and data compression) schemes. This source coding and decoding is carried out by codec equipment.

Serial and parallel transmission[edit]

In telecommunications, serial transmission is the sequential transmission of signal elements of a group representing a character or other entity of data. Digital serial transmissions are bits sent over a single wire, frequency or optical path sequentially. Because it requires less signal processing and less chances for error than parallel transmission, the transfer rate of each individual path may be faster. This can be used over longer distances as a check digit or parity bit can be sent along it easily.

In telecommunications, parallel transmission is the simultaneous transmission of the signal elements of a character or other entity of data. In digital communications, parallel transmission is the simultaneous transmission of related signal elements over two or more separate paths. Multiple electrical wires are used which can transmit multiple bits simultaneously, which allows for higher data transfer rates than can be achieved with serial transmission. This method is used internally within the computer, for example the internal buses, and sometimes externally for such things as printers, The major issue with this is 'skewing' because the wires in parallel data transmission have slightly different properties (not intentionally) so some bits may arrive before others, which may corrupt the message. A parity bit can help to reduce this. However, electrical wire parallel data transmission is therefore less reliable for long distances because corrupt transmissions are far more likely.

Communication channels[edit]

Some communications channel types include:

• Multi-drop:

Asynchronous and synchronous data transmission[edit]

Asynchronous serial communication uses start and stop bits to signify the beginning and end of transmission.^[7] This method of transmission is used when data are sent intermittently as opposed to in a solid stream.

Synchronous transmission synchronizes transmission speeds at both the receiving and sending end of the transmission using clock signals. The clock may be a separate signal or embedded in the data. A continual stream of data is then sent between the two nodes. Due to there being no start and stop bits the data transfer rate is more efficient.

See also[edit]

References[edit]

1. ^ ^abcA. P. Clark, 'Principles of Digital Data Transmission', Published by Wiley, 1983
2. ^David R. Smith, 'Digital Transmission Systems', Kluwer International Publishers, 2003, ISBN1-4020-7587-1. See table-of-contents.
3. ^Sergio Benedetto, Ezio Biglieri, 'Principles of Digital Transmission: With Wireless Applications', Springer 2008, ISBN0-306-45753-9, ISBN978-0-306-45753-1. See table-of-contents
4. ^Simon Haykin, 'Digital Communications', John Wiley & Sons, 1988. ISBN978-0-471-62947-4. See table-of-contents.
5. ^John Proakis, 'Digital Communications', 4th edition, McGraw-Hill, 2000. ISBN0-07-232111-3. See table-of-contents.
6. ^F. Foukalas et al., 'Cross-layer design proposals for wireless mobile networks: a survey and taxonomy '
7. ^'What is Asynchronous Transmission? - Definition from Techopedia'. Techopedia.com. Retrieved 2017-12-08.

Viruses are the most common biological entities on Earth. Experts estimate there are around 10,000,000,000,000,000,000,000,000,000,000 of them, and if they were all lined up they would stretch from one side of the galaxy to the other.

You can think of them as nature’s own nanotechnology: molecular machines with sizes on the nanometre scale, equipped to invade the cells of other organisms and hijack them to reproduce themselves. While the great majority are harmless to humans, some can make you sick and some can even be deadly.

Are viruses alive?

Viruses rely on the cells of other organisms to survive and reproduce, because they can’t capture or store energy themselves. In other words they cannot function outside a host organism, which is why they are often regarded as non-living.

Outside a cell, a virus it wraps itself up into an independent particle called a virion. The virion can “survive” in the environment for a certain period of time, which means it remains structurally intact and is capable of infecting a suitable organism if one comes into contact.

When a virion attaches to a suitable host cell – this depends on the protein molecules on the surfaces of the virion and the cell – it is able to penetrate the cell. Once inside, the virus “hacks” the cell to produce more virions. The virions make their way out of the cell, usually destroying it in the process, and then head off to infect more cells.

Does this “life cycle” make viruses alive? It’s a philosophical question, but we can agree that either way they can have a huge impact on living things.

What are viruses made of?

At the core of a virus particle is the genome, the long molecule made of DNA or RNA that contains the genetic instructions for reproducing the virus. This is wrapped up in a coat made of protein molecules called a capsid, which protects the genetic material.

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Some viruses also have an outer envelope made of lipids, which are fatty organic molecules. The coronavirus that causes COVID-19 is one of these these “enveloped” viruses. Soap can dissolve this fatty envelope, leading to the destruction of the whole virus particle. That’s one reason washing your hands with soap is so effective!

How Coronavirus Is Transmitted: Here Are All The Ways It Can ...

What do viruses attack?

Viruses are like predators with a specific prey they can recognise and attack. Viruses that do not recognise our cells will be harmless, and some others will infect us but will have no consequences for our health.

What Is Transmitted By Em Waves

Many animal and plant species have their own viruses. Cats have the feline immunodeficiency virus or FIV, a cat version of HIV, which causes AIDS in humans. Bats host many different kinds of coronavirus, one of which is believed to be the source of the novel coronavirus that causes COVID-19.

What Is Transmitted By A Wave

Bacteria also have unique viruses called bacteriophages, which in some cases can be used to fight bacterial infections.

Viruses can mutate and combine with one another. Sometimes, as in the case of COVID-19, that means they can switch species.

Why are some viruses so deadly?

What Is A Std

The most important ones to humans are the ones that infect us. Some families of viruses, such as herpes viruses, can stay dormant in the body for long periods of time without causing negative effects.

How much harm a virus or other pathogen can do is often described as its virulence. This depends not only on how much harm it does to an infected person, but also on how well the virus can avoid the body’s defences, replicate itself and spread to other carriers.

In evolutionary terms, there is often a trade-off for a virus between replicating and doing harm to the host. A virus that replicates like crazy and kills its host very quickly may not have an opportunity to spread to a new host. On the other hand, a virus that replicates slowly and causes little harm may have plenty of time to spread.

How do viruses spread?

Once a person is infected with a virus, their body becomes a reservoir of virus particles which can be released in bodily fluids – such as by coughing and sneezing – or by shedding skin or in some cases even touching surfaces.

How Are Diseases Transmitted? - Healthline

The virus particles may then either end up on a new potential host or an inanimate object. These contaminated objects are known as fomites, and can play an important role in the spread of disease.

What is a coronavirus?

The coronavirus COVID-19 is a member of the virus family coronaviridae, or coronaviruses. The name comes from the appearance of the virus particles under a microscope: tiny protein protrusions on their surfaces mean they appear surrounded by a halo-like corona.

Other coronaviruses were responsible for deadly outbreaks of Serious Acute Respiratory Syndrome (SARS) in China in 2003 and Middle East Respiratory Syndrome (MERS) from 2012. These viruses mutate relatively often in ways that allow them to be transmitted to humans.