| slovo | definícia |
multiplexing
(encz) | multiplexing,multiplexování n: Zdeněk Brož |
multiplexing
(foldoc) | multiplexing
multiple access
multiplexer
multiplexor
mux
1. (Or "multiple access") Combining several
signals for transmission on some shared medium (e.g. a
telephone wire). The signals are combined at the transmitter
by a multiplexor (a "mux") and split up at the receiver by a
demultiplexor. The communications channel may be shared
between the independent signals in one of several different
ways: time division multiplexing, {frequency division
multiplexing}, or code division multiplexing.
If the inputs take turns to use the output channel ({time
division multiplexing}) then the output bandwidth need be no
greater than the maximum bandwidth of any input.
If many inputs may be active simultaneously then the output
bandwidth must be at least as great as the total bandwidth of
all simultaneously active inputs. In this case the
multiplexor is also known as a concentrator.
(1995-03-02)
2. Writing multiple logical copies of data
files. Placing the copies on totally separate paths to
mirrored devices greatly reduces the probability of all
copies being corrupt. Multiplexing differs from mirroring in
that mirroring takes one data file and copies it to many
devices, thus making it possible to copy a corrupt file many
times. Multiplexing writes the data files to many places
simultaneously; there is no "original" data file.
(2001-05-10)
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| | podobné slovo | definícia |
code division multiplexing
(foldoc) | Code Division Multiple Access
CDMA
code division multiplexing
(CDMA) (Or "spread spectrum") A form of
multiplexing where the transmitter encodes the signal using
a pseudorandom sequence which the receiver also knows and
can use to decode the received signal. Each different random
sequence corresponds to a different communication channel.
Motorola uses CDMA for digital mobile phones. Qualcomm
pioneered the introduction of CDMA into wireless telephone
services.
(2001-03-28)
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frequency division multiplexing
(foldoc) | frequency division multiplexing
FDMA
frequency division multiple access
(FDM) The simultaneous transmission of
multiple separate signals through a shared medium (such as a
wire, optical fibre, or light beam) by modulating, at the
transmitter, the separate signals into separable frequency
bands, and adding those results linearly either before
transmission or within the medium. While thus combined, all
the signals may be amplified, conducted, translated in
frequency and routed toward a destination as a single signal,
resulting in economies which are the motivation for
multiplexing. Apparatus at the receiver separates the
multiplexed signals by means of frequency passing or rejecting
filters, and demodulates the results individually, each in the
manner appropriate for the modulation scheme used for that
band or group.
Bands are joined to form groups, and groups may then be joined
into larger groups; this process may be considered
recursively, but such technique is common only in large and
sophisticated systems and is not a necessary part of FDM.
Neither the transmitters nor the receivers need be close to
each other; ordinary radio, television, and cable service are
examples of FDM. It was once the mainstay of the long
distance telephone system. The more recently developed {time
division multiplexing} in its several forms lends itself to
the handling of digital data, but the low cost and high
quality of available FDM equipment, especially that intended
for television signals, make it a reasonable choice for many
purposes.
Compare wavelength division multiplexing, {time division
multiplexing}, code division multiplexing.
(2001-06-28)
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statistical time division multiplexing
(foldoc) | statistical time division multiplexing
StatMUX
STDM
(STDM, StatMUX) A system developed to
overcome some inefficiencies of standard {time division
multiplexing}, where time slices are still allocated to
channels, even if they have no information to transmit.
STDM uses a variable time slot length and by allowing channels
to vie for any free slot space. It employs a buffer memory
which temporarily stores the data during periods of peak
traffic. This scheme allows STDM to waste no high-speed line
time with inactive channels. STDM requires each transmission
to carry identification information (i.e. a channel
identifier). To reduce the cost of this overhead, a number of
characters for each channel are grouped together for
transmission.
["Data Communications, Computer Networks and Open Systems",
Halsall & Fred, Addison Wesley, p160-161, 1995].
["Digital, Analog, and Data Communication", Sinnema &
McGovern, Prentice Hall, p245, 1986].
(1997-03-05)
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time division multiplexing
(foldoc) | time division multiplexing
TDMA
time division multiple access
(TDM) A type of multiplexing where two or
more channels of information are transmitted over the same
link by allocating a different time interval ("slot" or
"slice") for the transmission of each channel. I.e. the
channels take turns to use the link. Some kind of periodic
synchronising signal or distinguishing identifier is usually
required so that the receiver can tell which channel is which.
TDM becomes inefficient when traffic is intermittent because
the time slot is still allocated even when the channel has no
data to transmit. Statistical time division multiplexing
was developed to overcome this problem.
Compare wavelength division multiplexing, {frequency division
multiplexing}, code division multiplexing.
(2001-06-27)
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wave division multiplexing
(foldoc) | wave division multiplexing
A common misnomer for {wavelength division
multiplexing}.
(2002-07-16)
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wavelength division multiplexing
(foldoc) | wavelength division multiplexing
DWDM
WDM
(WDM) Multiplexing several {Optical Carrier
n} signals on a single optical fibre by using different
wavelengths (colours) of laser light to carry different
signals.
The device that joins the signals together is known as a
multiplexor, and the one that splits them apart is a
demultiplexor. With the right type of fibre you can have a
device that does both and that ought to be called a "mudem"
but isn't.
The first WDM systems combined two signals and appeared around
1985. Modern systems can handle up to 128 signals and can
expand a basic 9.6 Gbps fibre system to a capacity of over
1000 Gbps.
WDM systems are popular with telecommunications companies
because they allow them to expand the capacity of their fibre
networks without digging up the road again. All they have to
do is to upgrade the (de)multiplexors at each end. However
these systems are expensive and complicated to run. There is
currently no standard, which makes it awkward to integrate
with older but more standard SONET systems.
Note that this term applies to an optical carrier (which is
typically described by its wavelength), whereas {frequency
division multiplexing} typically applies to a radio carrier
(which is more often described by frequency). However, since
wavelength and frequency are inversely proportional, and since
radio and light are both forms of electromagnetic radiation,
the distinction is somewhat arbitrary.
See also time division multiplexing, {code division
multiplexing}.
[Is "wave division multiplexing", as in "dense wave division
multiplexing" (DWDM) just a trendy abbreviation?]
(2002-07-16)
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