On Tue 12 Mar at 08:03 Rod Speed (3:711/934.2) wrote to Arthur Marsh:

AM> Unfortunately there can be be a Digital - Analogue - 
AM> Digital conversion at the exchange because Telstra didn't 
AM> have the right equipment to put in a direct digital link 
AM> between the exchange interface to a RIM or RCM and the 
AM> AXE / S12 switch at the exchange.

 RS> Oh sure, I wasnt attempting to describe all the configs that 
 RS> are seen, just pointing out to him that his idea that 
 RS> its currently an analog network has not been true for 
 RS> quite a while now.

True, and many people are not familiar with the example I described above
which could be described briefly as "multiple D/A-A/D
conversions" or "multiple PCM channels".

 RS> Be interesting to see whats causing the problem with Dave 
 RS> Hatch and if its due to some bodgy kludge up like that 
 RS> thats doing it.

No, it seems like there are problems with the line cards or something.
Frank Nitzsche is hard at work on it...

AM> This extra D - A - D conversion will stop V.34 modems from achieving 28800 
AM> bps at reasonably low Bit Error Rates.

 RS> True. Have you ever seen a decent freq response graph done Courier/Courier 
 RS> thru a link like that ?  Be interesting to know that it actually looks like 
 RS> on one of those.

No... maybe Frank Nitzsche could arrange a demo. I'm waiting on him to
release some graphs of impedence matching between modems and AXE and S12
exchanges versus copper losses (or more simply length of copper pair of a
particular gauge between modem and exchange).

 RS> That USR approach really is a hell of an advance, essentially being able 
 RS> to measure the line properly with the modems, tho currently there is some 
 RS> weird glitch which means that the results are a full 6db different 
 RS> right across the spectrum if there is either an M34F of Viper on the other 
 RS> end. Joe Frankowitz (USR) answer on that wasnt very helpful as to why, 
 RS> looks suspiciously like he hasnt come across it.

Hmmm... most of that information is needed by a V.34 modem to perform well,
it's just that USR went to the trouble to make it available to the end
user.

RS> it remains to be seen what gets delivered on those promises tho.

AM> Hint: Alcatel's Liverpool factory is quite busy enough 
AM> as it is, without having to produce RIM-ISDN gear at 
AM> twice the currently planned rate.

 RS> Maybe, but its just those sorts of promises that really do
 RS> shake the system up, as PayTV itself has in another area.

Also, RIM-ISDN hasn't proven itself in the field yet.

--- msgedsq 2.1