ADSL connection with Woody

[Kareem Shehata]

On Sat, 2003-09-20 at 17:40, Marc Lijour (Professeur d'Informatique)
wrote:
> More seriously, I believed that the filter was working to filter out the DSL 
> frequences from getting into your phone. I did not think that it worked in 
> the other way. And what in a phone could disrupt the line (especially when it 
> is just sitting here, off)?

First thing's first: a telephone wire is a transmission line.  From an
Electrical Engineering perspective, this is very important.  If you have
a sender attached to a transmission line that is open or shorted at the
end (or any other impedance mismatch), you get signal reflections.  Your
ordinary phone equipment is designed to terminate a specific set of
frequencies (i.e. voice band), but not the high frequencies on which 
xDSL operates.  DSL Modems are very sensitive to noise and transmission
line effects, hence the upper limits on distance from the CO.  Your
phone is likely causing a mismatched stub on the line, completely
messing up the transmission line between your modem and the DSLAM.  The
filter terminates the line correctly at DSL frequencies, yet allows
voice frequencies to pass unaltered.

In a nutshell:  standard phone equipment deals with voice stuff, but
messes up DSL.  DSL equipment deals with both.  Filter the phones, and
your modem will be fine.

HTH!

Kareem

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