[CLUG] [OT] Genesis (Is this actually OT?)

[Donnchadh Ó Donnabháin]

Owen Kelly wrote:
> 
> Most telephone people moan on and on about the bandwidth capability of telephone cable.  The theoretical
> bandwidth of phone lines is about 4-5 kHz.  So, instead of being your average modem, Im guessing that the
> "Black Box" Genesis use uses maybe 3Khz for bandwidth modem style, and then uses serious multiplexing of
> signals in the other 1.5kHz, increasing the range of data that can be transmitted dramatically.  Most modems
> only multiplex data using amplitude modulation, frequency modulation, or some other form that I cant
> remember, possibly due to some college social hangover ...
> 
> 56k standard is also about 3-4 years old, no one ever said that would be the last system to transmit data on
> good old copper phone lines.

  The reason 56K modems are limited to 56Kb/s not the line between the
user
 and the exchange, but the fact that the line is sampled at 8Ksamples/s
at 14bits
and converted to 8 bits using mu-law/A-law compression => 8x8K =
64Kbit/s. The line
 itself has much greater capacity than the 3400Hz bandwidth used by
POTS. 
Are Genesis going to connect to customers directly through their own
exchanges
 or are they going to get n*45Mbit/s interconnects to Eircom exchanges
at dirt-cheap
 rates and put their adapters/codecs in the Eircom exchange? 
 Then there's the issue of the channel capacity of the phone line. The
bandwidth
 of a phone line is more than 3400Hz but I don't think it would be
enough to 
give 45Mbit/s. xDSL already places strict limits on the quality of line
that can
 be used. Anyway the Hartley-Shannon Law gives the theoretical maximum
bandwidth:
  C = B lg(1 + S/N)) b/s
where lg is log base 2
S/N is signal to noise ratio
B is bandwidth
C is channel capacity in bits per second.
Also EMC regulations would prevent them just increasing the power level
 to improve SNR.

   Donnchadh