Text 11309, 61 rader
Skriven 2010-10-15 11:18:16 av Michiel van der Vlist (2:280/5555)
  Kommentar till text 11285 av Björn Felten (2:203/2)
Ärende: Weired vs wireless
==========================
Hello Björn,

On Wednesday October 13 2010 19:32, you wrote to me:

 MvdV>> And we all know that it ended at 56K.

 BF>    Not here. I have 2/0.4M on the very same copper wires with my ADSL
 BF> modem. Those who live close enough to the tele station can get up to
 BF> 24/2M.

Ok. My bad. I read it as "over a voice channel". Which of course is not the
same as "over a pair of wires".

Nobody ever claimed 56K was the limiet for a pair of copper wires. A POTS voice
channel however is limited to 56 kbps. (Actually 33kbps, the 56 kpbs is a trick
that only works on exchanges that are digtal, not POTS)

 MvdV>> No, you get the same number of channels per Hz. It just looks
 MvdV>> like there is more when you plot it on a logarithmic scale.

 BF>    Negatory. There is nothing that limits the amount of "channels" on
 BF> a specific "Hz". It all amounts to the technology used. Just as the
 BF> old 2400-channel could be extended on the same bandwidth by using
 BF> smarter modulations.

What actualy happened there is that part of a channel (the copper wire) that
was only used up to 3500 Hz because of limitations further down the road
(amplifiers, filters etc) is now used to its full capacity.

 BF>  The sky is the limit -- and that goes of course for the frequency
 BF> "roof" too.

No, that is not true. You can pipe more bit/sec though a given amount of Hz by
using a more complex modulation, but the price you pay is that you require
better signal to noise ratio and hence more power. Look up Shannon's law.

 MvdV>> The higher the frequency, the more difficult it becomes. The
 MvdV>> limit is when you drown in the thermal and solar radiation. The
 MvdV>> extreme high frequencies are only usable for very short range
 MvdV>> or point to point.

 BF>    All very true. With today's technology, mind you!

 MvdV>> Sure. But the same goes for data over "wire". Wireless will
 MvdV>> ALWAYS stay behind wire. That was my point.

 BF>    Oh, I thought the point was using mobile internet. :)

You claimed that the wireless internet would some day be "almost as big as the
wired internet". That is the claim I am countering.

I came across an interesting article that sums it up very nicely:

http://www.potaroo.net/ispcol/2010-08/wiredvswireless.html



Cheers, Michiel

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