Aug 11, 2017 At first, parallel connections might seem like better ways to send data - so why are most modern interfaces like USB serial? Visit https://www.tunnelbear.com. Serial And Parallel Data Transmission By ZAK 1. Page 1 of 7 1.2 Communication and Internet technologies 1.2.1 Serial and parallel data transmission TRANSMISSION OF DATA Data transmission refers to the movement of data in the form of bits between two or more digital devices.
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A few weeks ago, we published an article, about storage, and how data was transferred from a storage space to a machine; we will focus today on the methods of transmission of this data.
For each and every data transfer, there is one truth: the emitter and the receiver have to use the same protocol. It allows them to have the same level of information and to know the transfer speed of the data, the signals announcing the beginning and the end of the communication, as well as the method used to check the integrity of the received data. There are numerous protocols, which we developped in our aforementionned article. However, all protocols rely on two transmission methods: parallel transmission and serial transmission.
In this article, discover the differences between these two methods in terms of concept and use!
Bits
Before getting into the heart of the matter, let us have a quick “vocabulary break” and focus on bits. A bit is the smallest unit used to code data, and it can take only two values: 0 or 1.
Let us take ASCII code as an example. It enables to code a character with a byte (a byte is equal to 8 bits). The letter A, in this case, is written 01000001 in ASCII code, or:
A three-letter word, such as “cat”, is thus coded with three bytes, thus 3×8 = 24 bits, etc.
The two data transmission methods we expose in this article are acting at the bit level.
Parallel transmission
This data transmission method consists in sending bits between an emitter and a receiver on several lines, simultaneously. For instance, by associating 8 buses (cables) and transmitting 1 bit per bus at the same time, one has the opportunity to go 8 times faster as by progressively sending the data: it is the biggest advantage of this method. Moreover, it can easily be implemented on a machine, since creating a parallel port to receive the additional buses is very easy. Its drawback is its price: having several cables is much more expensive than having only one, whic makes sense! It is however possible to make parallel data transmission through only one physical line, by dividing the bandwidth into several underlying lanes.
Main use
Parallel transmission can be used for data transfer on a short distance, for instance between components of a machine (PCI protocol). However, for great distances, serial transmission is preferred: using parallel transmission would require too much equipment. Moreover, the longer the cable, the bigger the probability to experience crosstalk: it is a phenomenon of electromagnetic induction where the signal transmitted by one cable creates an interference with a signal on another cable.
Serial transmission
This data transmission method consists in sending succeeding bits through a single bus, between an emitter and a receiver. These bits thus reach the receiver one after the other, which can take time depending on the quantity of data to be sent.
In order to know when the transmission starts and when it ends, the sent data is organized in threads. A thread is made of a header, of data to transmit, and of a trailer (indicating the end of the transmission).
There are two serial transmission methods for these threads:
Synchronous transmission![]()
The emitter and the receiver are adjusted on the same clock, thanks to a synchronisation signal (a signal indicating the moment where the receiver can read data), for the reading frequency to match the sending frequency. Without this, the receiver is likely to read only one out of two bits, for instance, if its reading frequency is twice as slow as the receiving frequency.
For that, there are two solutions: either the signal is regular, in which case the receiver will synchronize its internal clock to the emmiter’s frequency, or it is not. In the later case, the synchonisation signal is sent through a second bus, whose goal is thus to synchronize transmissions, placed in parallel of the bus transmitting the data.
In both cases, data can be sent in an uninterrupted flow, since the receiver adjusts itself depending on the synchronisation signals.
Asynchronous position
With the asynchronous method, however, there has to be an inactivity interval inbetween two data transmissions. The data sending frequency does not count in this case. Indeed, within the general thread, the transmission of one single character is launched by a “starting” signal (or bit). Once the 8 bits of the character are transmitted, there is an “ending” bit indicating the end of the character transmission. The problem with this method is that 20% of the bandwidth is used by these framing bits. It is mainly used for small threads with a moderate pace.
This data division work, as well as the insertion of bits between a “starting” bit and an “ending” bit is made by the UART (Universal Asynchronous Receiver/Transmitter). To be able to send a character made of 8 bits, the emitter’s UART thus puts these between the framing bits. For each character, it thus has a shift register containing the character:
The UART starts by sending the starting bit, then shifts its register to the left.
The first bit is thus in the “sending” position: it is sent. It keeps going this way until the ending bit is sent.
At the receiver level, the principle is the same. The UART has an empty register, made of 10 cases. When it receives the starting bit, its register fills in this way:
The register then shifts to the left in order to receive the following bits, and thus obtain all the bits in the right order. In the end, the register is filled as such:
That is how the character is fully readable by the receiver.
Data integrity
In these two cases, one also has to check that all of the data has been transmitted. There are two ways to do this. The first one is to have a cyclic redundancy check: it is a software tool using the hashing method and enabling to spot transmission errors. The second one is to include, for each character, a parity bit. A parity bit takes the value 0 if the total of the other bits is an even number, and the value 1 if it is odd.
Main use
Serial transmission is mainly used for long distance (telecom, audiovisual media…). It can be found in the following protocols: optic fiber, USB, Ethernet, Fibre Channel, Serial Attached SCSI, PCI, SATA…
Use of these methods today
At the beginning of IT, data transmission was serial; then, the use of parallel transmission grew since it offered better performances. But in 2005, with the improvement of the electronics, serial transmission became comptetitive again: it now offers good performances, sometimes even better ones than parallel transmission, and it is less expensive since it needs less equipment. That is why we use USB disks rather than IEEE 1284, SATA rather than PATA…
Parallel transmission remains used in radio communication, where it is resurfacing, or even inside machines on short distances (with the PCI protocol for instance).
(Redirected from Comms)
Data transmission (also data communication or digital communications) is the transfer 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.
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 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.
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:
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:
Asynchronous and synchronous data transmission[edit]
Asynchronous serial communication uses start and stop bits to signify the beginning and end of transmission.[6] 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]
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Data_transmission&oldid=940598690'
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