Quote:
Originally Posted by The_bluester
We don't even know if the vaunted VDSL plus vectoring solution will scale up and actually work as described.
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Hi Paul,
From an information theory perspective, vectoring is tackling the wrong
part of the
Shannon-Hartley theorem.
The theorem states -
C = B * log2 * (1 + S/N)
Where
log2 is the log to the base of 2;
C is the channel capacity in bits per second;
B is the bandwidth of the channel in hertz;
S is the average received signal power over the bandwidth ;
N is the average noise or interference power over the bandwidth ;
S/N is the the signal-to-noise ratio (SNR)
What we are trying to do is maximize channel capacity.
One can either make S/N larger or make B larger or both.
What vectoring attempts to do is to make N smaller so as to make
S/N larger.
On a copper transmission line, a common noise source (N) in
practice comes about from what electrical engineers refer to as
Far End Crosstalk (FEXT).
FEXT in turn results from mutual inductive and capacitive coupling
and they in turn are a consequence of Maxwell's equations.
[The elegant vector calculus form of Maxwell's equations that
we most commonly see were formulated by
Olivier Heaviside,
an electrical engineer].
Vectoring attempts to mitigate the effects of FEXT.
But whatever we do to improve S/N will only improve the
channel capacity by a factor of log to the base 2, a relatively
flat curve.
For example, log2(2) =1 and log2(8) = 3.
The alternative is to improve B, which then provides a linear increase
in channel capacity. We increase B by many fold when going from
copper to optical fibre.
There are enormous other benefits a FTTP network has over FTTN
including that the former is passive - it has no electricity running
through it. This makes it far more reliable.
To bring about vectoring, one needs powered nodes in the street with
relatively high performance computing elements inside them. The failure
of most modern electronic systems is commonly rooted in thermodynamics
effects. You want to avoid points of failure such as boxes full of electronics
operating 24/7 in the heat and cold out on the street.
As we also know, including myself personally from the copper to my
own premise, the copper network in many streets has deteriorated past
its use-by date. It is literally falling apart.
A short while ago Malcolm Turnbull resigned as Communications Minister.
Image credit of log2 from Wikipedia Commons.
