From: dewey@vpdbox.austin.ibm.com (Dewey Coffman)
Newsgroups: austin.talk
Subject: Re: Info on ISDN
Date: 25 Aug 92 18:39:36 GMT
Reply-To: dewey@vpdbox.austin.ibm.com
Distribution: austin
Organization: IBM, Austin, TX. US of A.

In article <1992Aug21.215041.7563@chinacat.unicom.com>, chip@chinacat.unicom.com (Chip Rosenthal) writes:
|> In article <1992Aug17.153337.11667@awdprime.austin.ibm.com>
|> 	dewey@vpdbox.austin.ibm.com writes:
|> >
|> > * V.35, Data Transmission @ 48k baud, using 60-108 KHz group bank circuits.
|> >
|> >   -Retix, 1990 ISO & CCITT Data Communications Standards
|> >	
|> >I find the use of "baud" interesting. Maybe Chip Rosenthal will enlighten
|> >us how that is possible.
|> 
|> Sorry.  From lack of context I don't understand it either.
|> 
	That was the context. The Retix guide mentioned had a list of
	V.?? whatever and out beside it, a short description.

I also had the following information float my way...
-------------------------------------------------------------------------
From: csc@malone.austin.ibm.com (Chris Cheyney)

An ISDN TA isn't a V.35 beast that I know of ..... this sounds awfully
strange.  If I remember right, an ISDN TA is able to provide V.24
signaling (read: pretty close to RS-232-D).  The specific frequencies
mentioned also tell me that this is most likely NOT an ISDN TA.

Here's the deal.  Some telephone companies provide data services on
a "Data-Over-Voice" FDM sort of arrangement.  It just so happens that
the frequencies they provide this service over are about 60 kHz to
100 kHz or so.  The subscribers get modems which make the telco's
DCE look like an X.3 PAD.

An ISDN TA adapts a V.24 signal to a 56k-bit/s signal by bitstuffing.
To get the data rate required, you just stuff a certain ratio of
filler patterns so the TA on the other end knows what V.24 data rate
is being used.  The reference for the data rate is based on the
crystal clock in the interface card in the telco switch, and not
from anything on the customer's end.  This is also important to
note.

Also note that some ISDN manufacturers also claim that ISDN is 64k-bit/s
but it isn't because the switches require one's bit density and they get
it by bitstuffing.  The switches also have clock variances to the tune of
140 parts per million (if I remember the DS-0 specification) which also
decreases the data rate.

There's not a way to get 48 kilobaud out of the line using ISDN.
There is a way to get that using data-over-voice FDM.

My interpretation: The person who this person (ages ago in this chain)
talked to at the phone company probably had no idea what they were talking
about and just wanted to give some sales figures to someone.  The people
giving the figures out were reading from a prepared listing of prices for
services, and weren't about to make a sale, so they just went with what
they had and that was that.

Anyhow, you might want to check the specs but I think this is pretty
much right .....

Feel free to mention this in the group if you want .....
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ok, on both parts, next months CACTUS meeting is about ISDN. Be there.

-- 
Dewey Coffman				ibmpa!dewey@vpdbox.austin.ibm.com
Consulting @ IBM			Bldg 007, Div 44, Loc 966, Dept 06T
11400 Burnet Rd				Zip 1514, Room 1D-052
Austin, TX 78758-3493			(512) 823-6463
In article <21315@rpp386.lonestar.org>, jfh@rpp386.lonestar.org (John F. Haugh II) writes: "...I'm completely stupid, .."
Xref: sparky austin.talk:225 austin.general:2896