[asterisk-users] ISDN

[Joe Greco]

> >With ISDN, the conversion is done in your phone
>
> Exactly.  Or in the case of Asterisk, it is a 4 wire digital right into =
> the switch--no degradation.  Even converting back and forth between =
> analog and digital multiple times compromises quality.  Try doing a =
> dial-up modem across such a path.  The best you will get is 20 - 30 K.

A single D/A hop destroys the ability to do 56k.  Successful 56k requires
that there be a single A/D hop at the far end (the user's POTS interface)
and then digital delivery of signal the remainder of the way to the
terminating equipment. (modem -> phone co A/D -> digital to ISP modem
bank).

If you stick an extra D/A (maybe plus A/D) transformation in there, you 
will probably get fairly clean speeds in the upper ranges of 28.8-33.6,
but that'll be it (modem -> phone co A/D -> digital network -> phone co
D/A -> your buddy's modem).  If you're unlucky enough to get some crummy
phone co arrangement where they punt you back and forth from digital to
analog and back to digital within their network, that's even worse.