™ Traditional Modems
o Traditional modems are limited to a data
rate of 33.6 Kbps as determined by
Shannon's
formula Data rate ∝
Signal-to-noise ratio
o New modems with bit rated of 56 Kbps are
wide spread now
 |
o TX of data from A to B
o Digital data is modulated by the modem at
site A
o Analog
data is sent
from the modem
to to the
switching station at
site A using
the local
loop
|
o At the switching station, analog data is
converted digital using PCM
|
o Digital data travels through the digital
network of telephone company and arrives at
the
switching station of site B
o At the switching station , digital data
is converted to analog using inverse PCM
o Analog data is sent from switching
station at site B to the modem using the local loop
o Analog data is demodulated by modem at
site B
o The
limiting factor is
step 3. Here
the analog signal
is quantized to create
digital
signal.
The quantization noise resulting from this process limits the data rate to
33.6
Kbps
o The
TX of data
from site B
to site A
follows the same
steps and again
the limiting
factor
is quantization.
ŠRESULT:
The
maximum data rate in each direction is limited to 33.6 Kbps
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