From: varney@cbnewsd.cb.att.com (Al Varney)
Subject: Re: end-to-end digital on ISDN -- the real application
Organization: AT&T Network Systems, Lisle, IL
Distribution: na
Date: Fri, 8 Jan 1993 18:04:18 GMT

In article <PICONE.93Jan7174958@trdc001.trdc.ti.com> picone@trdc001.trdc.ti.com (Joe Picone) writes:

>Perhaps I should explain our real application and let you ISDN wizards
>out there solve the problems...
>
>I am interested in collecting large speech databases that represent
>good samples of the variation of speakers, telephones, channels, and
>the ambient conditions found in the "normal telephone network"
>(whatever that means these days).  Of course, we cannot sample all
>dimensions of the problem (collect data in every city, from every
>carrier , etc.).

   If that's the case ("...variation of ... ambient conditions"), why
would you want to bias the results by collecting samples that attempt
to bypass the D-A "reconversion" that occur for normal calls???
I'd think you would want to collect samples from various callers AND
from various types of line terminations.  Are you sure that you aren't
really interested in a "speech" database that DOESN'T include the effects
of the telephone network?

>Two scenarios we have used in the past are the following 
 [details deleted]

>Case 1 suffers from the fact that at the receiving site there is a fixed 
>analog line from the local office to the data collection machine.
>This does impose an additional and unnecessary A/D conversion.

   But it represents the "real telephone network"...

>Case 2 suffers from the fact that the data collection system is a PC
>and T1s are unmanageable for us novices.
>
>So, now that Sun Sparcstation 10s have ISDN interfaces built in,
>we can replace Case 2 with an ISDN interface. Sounds too good to
>be true...
>
>The question was raised: how does the data collected in such a manner
>compare to the T1 connection in Case 2. My instinct is that doing this
>type of data collection with ISDN will be as good, certainly no worse, 
>than the T1 case, and definitely better than Case 1.
>
>Others have raised concerns that there might be, on the average,
>more re-conversions performed.
>
>ISDN gurus please comment...

   I'm not one, but that's never stopped me before!! :-)  ISDN on YOUR
end would be very similar to Case 2 in preservation of the signal.  It
obviously would be more flexible than the PC system (does it ever drop
samples??  What does it do with the A/B bits, if anything?).
ISDN could also be cheaper than the T1, but obviously depends on usage
and SW Bell's tariffs.  You could run a side-by-side trial for a while;
have the T1 system direct callers to call another 800 number and do the
same thing into the ISDN system.

   ISDN on the CALLERS end would remove the big three sound mutilation
sources in the customer-to-EO loop (cheap phones & other junk on the line
[FAX,modem,other phones], loop noise/loss/echo, customer's wiring).  
But that would mean your samples would NOT represent the "real world"
telephone network.

   ISDN vs. T1 could result in an added "re-conversion" (in the LEC),
but if you are on an ISDN-capable EO, that's not likely in Dallas.
The primary AT there is a 4ESS(tm) digital switch, so even calls that
aren't direct will almost certainly stay digital.  

   As I've mentioned before, I think you are unduly worried about
"re-conversions" at an analog switch.  In metro areas (and many others),
the analog switch + analog facilities will generally be very short
(<500 feet) connections between the 2 A-D converters.  If the converters
are good, they should add a very small error into the total call.

   You are going to get more distortion from "Toys-R-Us(sm)" cheap
telephones than from a typical telephone network connection, IMHO.
Maybe you should have the callers identify the brand/type of telephone
they are using....

  Al Varney - just MY opinion

Al Varney