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1995-01-22
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247 lines
(in the US) Carrier, TWO copper pairs are required. Your "ordinary"
telephone line can support 144 Kbps (BRI ISDN) - not just the 30 Kbps
that you might get from analog technology -- that was an apple and
orange comparison.
> Has anyone ever used/seen a PRI? The above is just a guess because I
> have not seen/used one. PRI/T1 are, I heard, usually run over 2
copper
> pairs (4 wires). This means that your ordinary telephone line should
> at least be able to run at 1 Mbps per pair. And ISDN Basic Rate
(BRI)
> runs at 192kbps. The telephone company wants you to pay different
> prices for services over the same old pair of copper wire.
The ability to operate anything over copper is dependent on the
quantity of impedance loss. You could get 150 Mbps to work over a
single pair of copper if it's only 6 ft long. The process of
delivering bandwidth over any medium has more to do with how to
deliver the signal with minimal loss than anything else. What the
telephone company wants you to pay for is the cost of maintaining a
quality and low loss signal to your home/office and the equipment it
takes to get it there.
To imply that the same or less equipment investment by the telco's is
required to deliver telephone (voice) grade service and high bandwidth
digital service over the same pair(s) of wires is not just ludicrous -
it displays a complete lack of understanding on the technology in
question and serves only to further confuse those that do not spend
their days and nights in the industry.
I would sincerely hope that you refrain from providing us with more
seemingly technical responses that have no basis in fact in order to
express your own opinions referecincing something you obviously know
considerably less about than you think.
My suggestion: Read more - type less.
Ed Goldgehn
[I've never worked for a telephone company, so this response is not at
all
biased by who pays my salary - just for the record].
------------------------------
From: jhallen@world.std.com (Joseph H Allen)
Subject: Re: What is a T1 Line?
Organization: The World Public Access UNIX, Brookline, MA
Date: Mon, 26 Dec 1994 03:21:44 GMT
In article <telecom14.469.17@eecs.nwu.edu>, L S Ng
<lsn92@ecs.soton.ac.uk>
wrote:
> The reason why T1 can run at 1.5Mbps plus whereas your ordinary
telephone
> line can run only at 30kbps is because of a low pass filter! Low
pass
> filters are inserted at the end of the ordinary telephone lines for
two
> reasons: to improve speech quality and (more importantly) to limit
your
> modem speed!
I think there's more to it that that. At 1.5Mbps (a signal needing
>3MHz bandwidth) the crosstalk should be pretty severe in a large
bundle of twisted pairs. This would prevent you from giving T1s to
everyone.
> Has anyone ever used/seen a PRI? The above is just a guess because I
> have not seen/used one. PRI/T1 are, I heard, usually run over 2
copper
> pairs (4 wires). This means that your ordinary telephone line should
> at least be able to run at 1 Mbps per pair.
The loss at 1Mbps on both twisted pair and coaxial is pretty high.
This means you would need lots of repeaters. I don't think with voice
that you need any repeaters between home and local office. So at the
very least, they have to add lots of repeaters everywhere.
> 2Mbps is the limit of working in full duplex mode. In some
> applications such as video/TV, it is possible to pump more than
6Mbps
> down the copper wires. This technique is known as ADSL
(Asymmetrical
> Digital Subscriber Loop) and it is half duplex. British Telecom was
> blocked by Bristish Government last month from using this technology
> for broadcasting TV over the old copper telephone networks to home.
> The technology is ready but the bureaucrats are not.
I'd really like to see a detailed technical description of how this is
done. Perhaps they transmit at a different carrier on each pair in
the bundle? I really don't see how else they would get rid of the
cross-talk.
jhallen@world.std.com (192.74.137.5) Joseph H. Allen
------------------------------
Subject: Re: T1 + Ethernet -> Fiber
From: drharry!aboritz@uunet.uu.net (Alan Boritz)
Date: Mon, 26 Dec 94 07:00:25 EST
Organization: Harry's Place - Mahwah NJ - +1 201 934 0861
Paul A. Lee </DD.ID=JES2CAOF.UEDCM09/@SMX.sprint.com> writes:
>> My company is upgrading both their computer system (my
responsibility)
>> and their phone system (outside contractor). In the process, we
are
>> installing a cable between two sites. Currently, this cable will
contain
>> a fiber pair for linking two lans together and 75-pairs of copper
for the
>> PBX.
>> The fiber costs $.45 per foot and the copper costs ~$1.10/foot.
The
>> distance is 3000 ft.
> First and foremost, consider the installation cost and plan for the
> future. The cost of either fiber or copper is relatively small,
> compared to the cost of installing the cable. Installation costs can
> range from $4 per foot for shallow plow-in under turf to $30 or more
> per foot for a ducted installation under pavement.
I think you're missing much more important point. Fiber facilities
cost much less to provide, but they're more difficult to maintain than
copper. If you install it sloppy, like NY Tel, you can't even be
certain that some inadvertent local power loss (entirely beyond your,
and telco's, control) could shut you down completely. If you don't
control all of the points on a fiber network (and provide
uninterruptable
power for mux's and other critical equipment), you don't have much of
a network. The last major power failure in lower Manhattan
illustrated
that point very well, when NY Tel customers in the financial district
went without telephone service for days (even after their own office
electrical power was back on) because there was no power to run the
fiber facilities.
Compare the installed cost of fiber AND all of it's ancillary
equipment
(that bring it's reliability up to that of copper facilities) and
you'll have a TRUE comparison of fiber vs. copper.
aboritz%drharry@uunet.uu.net or uunet!drharry!aboritz
Harry's Place (drharry.UUCP) - Mahwah NJ USA - +1-201-934-0861
------------------------------
From: holloman@Cybernetics.NET (Robert F. Holloman)
Subject: Re: Disabling Call Waiting
Date: 25 Dec 1994 19:24:04 GMT
Organization: Cybernetx, Inc.
> entered it in the beginning. The trick is, if the recipient of the
> call wants to do that from the very beginning, he has to go off hook
> long enough to establish the connection, flash, enter *70 and get
back
> to the call in a timely way without having first allowed his modem
to
> answer (or at least not sending tones to the other modem). PAT]
I ran into this problem several years ago and have done quite a bit of
experimenting with it. Here's my own little mini-faq that I post
anytime
I see someone bring up this issue.
You should be able to disable Call Waiting on incoming calls by using
"ATDT!*70R|" (or a variation of this) in place of "ATA|". This won't
work when the modem's auto-answer function is being used. Also it
won't work if your phone system doesn't allow you to cancel CW while a
call is in progress. Or you might have to have three-way conference
calling. Works fine without three-way calling here on the Southern
Bell and the United Telephone exchanges I've tried it from. All have
been DMS-100 switches. In a few areas *70 (sometimes called "Call
Waiting Control") is an extra-cost feature you must order.
It works like this:
1) "AT" gets the modem's attention.
2) "D" tells them modem to go into originate mode, go off-hook, and be
ready to dial. (Caller's modem is waiting for answer tones.)
Modem will also check for dialtone, if you have dialtone detection
enabled (X2, X4, etc). Since there is no dialtone in this
situation, you must put "X3" in your init. string. Or you could
put it in this string after "AT" ("ATX3DT!*70R|"). (If you do the
latter, you'd probably want to make your regular dial prefix
"ATX4DT*70," or such.) With some modems, such as Intels, dialtone
detection can be overridden by changing "D" to "H1D," (or "DT" to
"H1DT," - same difference).
3) "T" tells it to use tone dialing. Needs to be "P" for pulse lines.
4) "!" flashes the line, which puts the caller on "hold" and gives a
dialtone. If your modem flashes too soon after going off hook
(like the USR Sportster), put a "," before the "!". If your modem
dials too soon after flashing, it will be necessary to put a ","
(or "W") behind the "!".
5) "*70" ("70#" in some areas, "1170" for pulse lines) cancels CW. It
should automatically switch back to the caller. If it doesn't
switch back, add a "!" behind the "*70".
6) "R" tells the modem to "reverse" to answer mode. You may need a
"," before the "R" to prevent truncation of answer tones. Because
"R" is meant to be used when calling originate-only modems (e.g.
"ATDT555-1234R|"), some modems will listen for ringback, followed
by a lack of ringback, before generating the answer tones. Since
there is no ringback in this situation, some of these modems will
wait too long before trying to connect. For these, change "R" to
";A". If that doesn't work, change "R" to ";|~~~~~~~~~~~~ATA"
instead. The ";" along with the "|" (see #7 below) causes the
modem to go into command mode after dialing. Each "~" causes the
comm program to pause for 1/2 second. Twelve of them here causes
the program to wait six seconds before sending "ATA" to the modem.
Add more or less to optimize the command. (Your program might use
a different character and/or the pause might not be for the same
duration.)
7) "|" is the same as pressing <ENTER>. Leave out this character when
entering command from terminal mode. (Some comm programs use
something different, such as "^M".)
"ATH1DT,!*70;A|" worked best when I had a 2400EX Intel.
"ATX3DT,!*70,X4R|" works best with my USR Sportster and phone system.
(The "X4" just turns back on dial tone detection. I believe most
non-USR modems won't understand such a command occurring after the
"D"ial command.)
Please leave me a reply if you know of any more IF's I should add.
------------------------------
End of TELECOM Digest V14 #470
******************************