Guys
I am really enjoying the lively discussions regarding
broadband and possible data transfer rates.
Altough an electrial engg. student is the one to
answer the questions, I choose to ask the questions...
Please remember that Ashwin is an authority on such
matters, and I, but a second year student. Please be
kind with me.
However, I am confused by some facts he mentioned and
I basically want to clear my confusion..
>>And then technically specify, if 186 Kbps (capital K
stands for Kilobytes - i.e. for kilobits this becomes
186*8 kbps)
I am abolutely sure that incase of (network) data
transfer rates, a KBps translates to 10 Kbps and NOT 8
Kbps
That is, a 186 Kbps connection will yeild a 18.6
Kilobytes per second thoroughput.
(Lookup Andrew S. Tanenbaum's "Modern OS", Pg. 66-67)
I quote :
"For measuring memory sizes, kilo means 2^10 rather
than 10^3.....
However, a 1Kbps connection transmits 1000 bits per
second...."
I would gladly stand corrected provided an authentic
reference is cited.
>>Cable TV networks are one way i.e. broadcast only.
Very true. Maybe because Cable TV networks signal in
analog domain whereas the most widely used protocol
for sending digital packets onto wild networks
requires the clients to ACKnowledge on receipt of
packets ?
AFAIC, the only thing common between Cable TV and
broadband over Cable TV is the copper coaxial wire !
Twisted pair cables suffer a high rate of attenuation
and noise at high freq. They have high impedance due
to skin effect and radiate out a lot of energy.
Coaxial cables eleminates both these problems, plus
there is negligible cross talk between cables due to
shielding effect..
>>What is the MPEG format (CD format) for such movie
CDs ? How many kilobits per sec for playback ?
112KBps per channel audio (224 KBps, MPEG 2), ~1.5
MBPs video for MPEG - 1 ?
OK - let me put it this way : Say you and I talk over
the phone for 10 Mins. If I were to record our
conversation at phone quality (~56Kbps ?), would I be
able to send you the file in 10 minutes ?
Just consider this - everybody in Kolkata listens to
FM radio, right ? They listen to CD quality music. But
then why is Reliance/TATA Indicom unable to provide
even 112Kbps ??
Would I be wrong in saying that at the wire level we
have Digital-To-Analog and Analog-Digital convertors
working at tandem, and there is the overhead of an
essentially packet switched network, etc..
As far as my seminal knowledge in communications go -
it's all because of the digital and analog signal
domain.
In analog systems, the main goal is to get a suitable
output signal-to-noise ratio. It directly affects how
the listener percieves the message.
However, in digital communications, we ALREADY know
what the possible symbols transmitted are - 0, 1.
Thus, we are not worried about reproducing the
waveform with fidlelity, because the possible
waveforms are known beforehand.
Our goal is to extract, from the noisy signal, which
of the waveforms have been transmitted.
You just cannot transmit a digital sample the same way
you can transmit an analog signal.
Am I right ? Please ruthlessly point out my errors as
I would have to site for an exam which will ask me
such questions in about 4 months from now :D
PS : Should this have been an off topic ? An offlist
post ?
Regards
Subhobroto Sinha
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