From: lars@CMC.COM (Lars Poulsen)
Newsgroups: comp.dcom.telecom
Subject: Some Questions on Public Data Networks
Date: 9 Nov 92 00:15:57 GMT
Organization: CMC Network Systems (Rockwell DCD), Santa Barbara, CA, USA
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 12, Issue 827, Message 2 of 4

[Moderator's Note: The original of this message was in issue 818 of
TELECOM Digest on Monday, November 2. It then circulated in comp.dcom.
telecom over the November 2-4 period. Apparently Sahsidhar is so busy
cross posting to various newsgroups that he does not bother reading
his articles later.  PAT]

In article <92307.085325KONDARED@PURCCVM.BITNET> 

   (appearing in comp.dcom.isdn) Sashidhar Kondared (?) writes:

> I have some questions on Public data networks for which comp.dcom.telecom
> may be more approriate, but its moderator doesn't seem to think so. I think
> someone on this group can easily clarify my doubts with out any reference to
> secondary info sources. Any response would be greatly appreciated.

I am surprised that PAT would discourage this; I am cc'ing TELECOM on
this response, in the hope that he may reconsider.

> *  Value added networks of common carriers (like AT&T) never cross paths
> with their voice networks. ie traffic on one never use the other network.
> Am I right?

I think you are wrong. SprintNet, ACCUNET and their cousins are using
cicuits provisioned in the same way that customers' leased lines would
be provisioned. This means that these circuits typically will be
sharing multiplexed trunks with interoffice trunks from the voice
network.

I.e. a handful of 56 kbps data circuits may be multiplexed together to
form a T1 circuit. (That same T1 may also be carrying some 56kbps
lines from the SS7 network supporting the voice network.) Likewise, a
number of voice trunks from your local toll access switch to the next
toll switch down the road may be multiplexed together on a T1. These
two T1's may be multiplexed together on a T3 fiber, along with some
T1's that were sold that way.

> *  Public data networks (common carrier VANs, Tymnet, Telnet etc) are not
> as extensive as plain old telephone networks. ie if someone in some
> remote place in say oklahama wants a data connection , most probably he
> will not get it. Is this right?

Yes, and no. Plain old telephone service is available just about
everywhere, because it is the government's policy that it should be.
On the other hand, no carrier is required to offer data service unless
they think they can make money on it.

But some form of data service is available just about anywhere.
Certainly, if you can get telephone service, you can dial up a modem
connection. If you can get a leased voice-grade line (and I think you
can get that almost anywhere, although you may have to pay for laying
the wire, if there isn't a wire already) you can set up a leased
dataline with modems. The value added carrier will typically offer you
service at their point of presence, and if you can get your data
there, you can use the service. Mostly, in metropolitan areas, I think
they prefer to sell the service at your premise, and THEY lease the
access line; this lets them earn a profit on the access line, and in
principle cuts down on the fingerpointing.

> *  Internet, Bitnet 'et. al.' do not use any public data network -
> they have their own infrastructure which is not shared with anyone.
> Is this right?

"There is no network called Internet". The Internet is a loose
connection of networks that use the same protocol stack. Each of the
"member" networks is separately provisioned. Most links are leased
digital data service lines, from 56kbps all the way up ... NSFnet's
backbone consists of 45Mbps (T3) links provisioned by MCI. Some links
out near the edges are dial-up links using asynch V.32bis modems (see
footnote).

So these networks "have their own infrastructure" in the sense that
they see some private lines, but the actual "wire" between cities is
likely to be part of a phone company fiber.

> *  Common carrier offerings like Frame Relay, SMDS do not use their plain
> old voice infrastructure. I'am wrong. Right?

Frame relay networks are generally built in a similar fashion as the
above mentioned X.25 networks.

SMDS is intended to be a more streamlined pipe for data into the
higher levels of the ISDN hierachy. SMDS uses phone numbers as data
link addresses.


Lars Poulsen, SMTS Software Engineer	Internet E-mail: lars@CMC.COM
CNC Network Products / Rockwell Int'l	Telephone: +1-805-968-4262	
Santa Barbara, CA 93117-3083		TeleFAX:   +1-805-968-8256

Footnote: My company just announced the NetHopper; a low-cost dial-up IP
router, which will connect your local ethernet to the Internet by
automatically dialing up a modem connection when there is traffic.


[Moderator's Mote: You are correct Lars. I did use his message
although it was around for a couple days in the queue with a few
hundred other submissions waiting for attention.  I wish people would
take the time to *read* each issue -- or at least scan it -- before
writing to me saying their article was not used. This gentleman has
since posted a summary of responses received. I will run it in the
next issue of the Digest.   PAT]