o Whenever
the TX capacity
of a medium
linking 2 devices
is greater than
the TX
Introduction
needs
of the devices, the link can be shared
o Example: Large Water pipe can carry water
to several separate houses at once
o Multiplexing is the set of techniques
that allows simultaneous TX of multiple signals
across
a single data link
o As data communication usage increases,
traffic also increases
o We can add a new line each time a new
channel is needed
o Or we can install higher capacity links
and use each to carry multiple signals
o All current TX media i.e. Coax, Optical
fiber have high available BWs
o Each of these has carrying capacity far
in excess of that needed for one signal
o If
TX capacity of
a link is
greater than the
TX needs of
devices attached to
it, the
excess
capacity is wasted
Multiplexing
Set of
techniques that allows
the simultaneous transmission of
multiple signals
across
a single data link"
In
the multiplexed system, 'n' devices share the capacity of one link
o Fig. shows two possible ways of linking 4
pairs of device
o In fig. (a), each pair has its own link.
If full capacity of each link is not utilized, it
will
be wasted
o In fig. (b), TX b/w pairs are multiplexed
. The same 4 pairs share the capacity of
single
link
o Fig. (b) shows the basic format of a
Multiplexed system
o The 4 devices on left direct their TX
streams to a MUX ,
which combines them
into
a single stream
o At
the receiving end,
that stream is
fed into a
DEMUX, which separates
the
stream back
into its component
transmissions and directs
them to their
intended
devices
Path: Physical
Link
Channel: A portion of
the path that carries TX b/w a given pair of devices
One path can
have many channels
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