Transfer of data over a point-to-point or point-to-multipoint communication channel
"Data transfer" redirects here. For sharing data between different programs or schemas, see
Data exchange
.
Data communication
, including
data transmission
and
data reception
, is the transfer of
data
,
transmitted
and received 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.
Analog transmission
is a 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
is carried out by
modem
equipment.
Digital communications
, including
digital transmission
and
digital reception
, is the transfer of
either a
digitized
analog signal or a
born-digital
bitstream
.
[1]
According to the most common definition, both baseband and passband bit-stream components are considered part of a
digital signal
; an alternative definition considers only the baseband signal as digital, and passband transmission of digital data as a form of
digital-to-analog conversion
.
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
communication 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.
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 modulated
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:
It is also common to deal with the cross-layer design of those three layers.
[7]
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. The first practical method to overcome the problem of receiving data accurately by the receiver using digital code was the
Barker code
invented by
Ronald Hugh Barker
in 1952 and published in 1953.
[8]
Data transmission is utilized in
computer networking
equipment such as
modems
(1940),
local area network
(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) 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. Digital communication to the end user using
Integrated Services Digital Network
(ISDN) services became available in the late 1980s. 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 with
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 compared to the multiplexing of analog signals. Because of all these advantages, because of the vast demand to transmit computer data and the ability of digital communications to do so and because recent advances in
wideband
communication channels
and
solid-state electronics
have allowed engineers to realize these advantages fully, digital communications have grown quickly.
The digital revolution has also resulted in many digital telecommunication applications where the principles of data transmission are applied. Examples include
second-generation
(1991) and later
cellular telephony
,
video conferencing
,
digital TV
(1998),
digital radio
(1999), and
telemetry
.
Data transmission, digital transmission or digital communications is the transfer of data over a point-to-point or point-to-multipoint communication channel. Examples of such channels include 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 light.
While analog transmission is the transfer of a continuously varying analog signal over an analog channel, digital communication 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 a 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.
[
citation needed
]
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 and a check digit or
parity bit
can be sent along with the data easily.
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 typically used internally within the computer, for example, the internal buses, and sometimes externally for such things as printers.
Timing skew
can be a significant issue in these systems because the wires in parallel data transmission unavoidably have slightly different properties so some bits may arrive before others, which may corrupt the message. This issue tends to worsen with distance making parallel data transmission less reliable for long distances.
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.
[9]
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 may be more efficient.
See also
[
edit
]
References
[
edit
]
- ^
a
b
c
A. P. Clark, "Principles of Digital Data Transmission", Published by Wiley, 1983
- ^
David R. Smith, "Digital Transmission Systems", Kluwer International Publishers, 2003,
ISBN
1-4020-7587-1
. See
table-of-contents
.
- ^
Sergio Benedetto, Ezio Biglieri, "Principles of Digital Transmission: With Wireless Applications", Springer 2008,
ISBN
0-306-45753-9
,
ISBN
978-0-306-45753-1
. See
table-of-contents
- ^
Simon Haykin, "Digital Communications", John Wiley & Sons, 1988.
ISBN
978-0-471-62947-4
. See
table-of-contents
.
- ^
John Proakis, "Digital Communications", 4th edition, McGraw-Hill, 2000.
ISBN
0-07-232111-3
. See
table-of-contents
.
- ^
"X.225 : Information technology ? Open Systems Interconnection ? Connection-oriented Session protocol: Protocol specification"
.
Archived
from the original on 1 February 2021
. Retrieved
10 March
2023
.
- ^
F. Foukalas et al.,
"Cross-layer design proposals for wireless mobile networks: a survey and taxonomy "
- ^
Barker, RH (1953).
Group Synchronisation of Binary Digital Systems
. Communication Theory: Butterworth. pp. 273?287.
- ^
"What is Asynchronous Transmission? - Definition from Techopedia"
.
Techopedia.com
. Retrieved
2017-12-08
.