
In article <telecom14.470.8@eecs.nwu.edu>edg@ocn.com (Ed Goldgehn)
says:

> T-1's require TWO pair of copper.  ISDN (BRI) requires ONE pair of
> Copper.  Since a Primary Rate (not Access) Interface rides on a T-1
> (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.

Technically, BRI ISDN is 2-64K B chanels, 1 16K D channel and another
16K channel for Telco maintenance use totaling 160K or 80K baud
capacity.  Not nitpicking, just thought you might like to know that.
And the above is the NORMAL configuration, there are several others.

Also, BRI ISDN can go upto 18, 000 feet from the actual serving office
before it requires any type of regenaration.

And talking about T-1 facilities, there is a new type called HDSL. It
stands for High Density Subscriber Loop. It is a FULL Duplex 768K on
two NON conditioned copper pairs that provides the 1.54mbit speed.
The 18,000 ft limit can be surpassed by a regenarator. The bridge tap
allowed is <2K ft.  AND there is NO separation needed in the cable.
AND it works! :) [I was skeptical at first when I saw one]

Why use them? CHEAP to install. The cable does not need to be
conditioned for T-1 carrier. No span repeaters or group separation is
needed. Thusly an enginerring job is not required.

The original poster is from England and the telco's over there are
vastly different in there usage of copper and fiber.


Scott Darling    Telco installer 

------------------------------

From: balcroan@netcom.com (Butch lcroan/.nameBalcroan Lilli)
Subject: Re: What is a T1 Line?
Organization: NETCOM On-line Communication Services (408 261-4700 
guest)
Date: Thu, 29 Dec 1994 17:37:40 GMT


Joseph H Allen (jhallen@world.std.com) wrote:

> 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!

The reason for the filters is to prevent some carrier above 3300HZ
from entering the A to D convertor and being multiplexed into the T1
which runs at 1.5MHZ . The reason for this is numerous and preceded
<MODEMS by quite a few yaers. The evil telephone company did this not
prevent you from sending higfh speed data as you implied ... there is
something called the Nyquist Law at work here that says you sample at
two times the fundamental frequency!

------------------------------

From: dos@spam.wdns.wiltel.com (Dave O'Shea)
Subject: Re: What is a T1 Line?
Date: 29 Dec 1994 20:14:08 GMT
Organization: WilTel
Reply-To: dave_oshea@wiltel.com


Joseph H Allen (jhallen@world.std.com) wrote:

> 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!

Well, not quite. Typically, a voice call that goes through a digital
circuit (which is true for almost all non-local calls these days) gets
fed into some variant of an FXS or SLIC, which breaks the analog
conversation down into a 56k data stream.

Once broken down into that neat little stream -- which often happens
before you even get to the CO in many urban areas -- the call is
placed into a data channel on a T1. So, you see, the fact that you
have telephone service doesn't guarantee you your own copper even a
foot past the premises.

We happen to be in a nice, modern building, so the total length of the
copper is only about 150 feet, from the telephone room, across the
warehouse, and down into NJ Bell's "shack". From there, it does right
into a fibermux, and it's a 56k stream on a DS3 before it hits the
sidewalk. If I make a long distance call, it goes digital before it
even leaves the switch.

In some cases, your already-digitized call may be packetized for some
sort of cell-relay arrangement. In this case, you don't even have a
time slice on a DS1 anymore, unless you're actually talking.

So, when I ring up someone in another city, I'm not actually paying
for a straight copper run from one end to the other -- I'm just buying
bandwidth for the period that I use it.

> 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.

Certainly given the state of some of the wiring that's out there. With
good-quality copper and proper termination, 10mhz signalling (a la
10baseT) is achievable for decent distances today, and I think most
people expect both the bandwidth and distance to grow, with the price
of the equipment coming down.

It's the long-haul bandwidth that's expensive, and the equipment that
it takes to switch it.

>> 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.

If users want more bandwidth, the carriers seem quite eager to bring
it in. I don't expect we're really going to see a big drop in the cost
of high-capacity private circuits anytime soon, though, unless someone
comes out with an application to use it.

>> 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.

I'm not familiar with the technique, but I'd guess it's analogous to
the v.42 compression used by commercial modems; you put intelligent
equipment at each end that can spot and tokenize repetitive data
streams.


Dave O'Shea                         dave_oshea@wiltel.com
Technical Development Manager       201.236.3730
WilTel Communications Systems       Did I *say* I'm a WilTel 
spokesman?

------------------------------

From: mpd@adc.com (Matthew P. Downs)
Subject: Re: What is a T1 Line?
Date: 29 Dec 1994 14:29:42 GMT
Organization: ADC Telecommunications


lsn92@ecs.soton.ac.uk (L S Ng) writes:

> Edward F. Munro writes:

>> If T1 is 24 X 64K on 4 wires, and ISDN is 2 X 64K, then why do you 
only get

>> 4 X 64K when you use 2 ISDN links?  Is there a way to get 2 ISDN 
lines and 
>> set yourself up with T1 bandwidth?!?

> I thought T1 has now been repackaged by the telephone companies as
> ISDN Primary Access or Primary Rate ISDN (PRI), consisting of up to 
24
> B channels (1.5Mbps) in North America or 30 B channels (2Mbps) in 
'the
> rest of the world'.

T1 is just a line format. PRIMARY rate uses this in order to make
higher rate connections.  The underlaying technology even to primary
rate is a T1 line with 24 DS0's each at 64 kbps.

> Originally T1 or Primary Access were used only within the telephone
> networks (from one local exchange/central office (CO) to another), 
but
> now it seems that, by packaging it as PRI, such rate now runs from 
CO
> to customers premises (your office/home). Each T1 link is 
essentially
> either a copper pair or an coaxial cable. 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!

Who has telephony via coax right now in the field? Right now each one
is either a copper or optical fiber connection.  There is a difference
between coax and fiber. These filters are not to limit your modem
speeds, but to protect you 64 kbps channel from others.  So you don't
hear the cross talk on your line!  This was done a long time before
modems were ever thought of ...

> So remember this: when you ask for ATM from your telephone company,
> make sure you get an optical fibre. Or they would give you a copper
> coax for 150Mbps and ask for more money when you need to 'upgrade' 
it
> to 600Mbps.  It is not possible to use copper coax at 600Mbps which 
is
> why you need a piece of cheap glass wire, otherwise known as the
> optical fibre by the telephone companies who want to glamorised 
their
> product names.

A lot of things are stated as fact that are not in this ... such as
with SONET.  They are not planning on giving any one a 150 mpbs or
even 600 mbps links.


Matt

------------------------------

From: stans@panix.com (Stan Schwartz)
Subject: Re: '500' Numbers Finally Available
Date: 29 Dec 1994 01:45:04 -0500
Organization: PANIX Public Access Internet and Unix, NYC


The Toddster (todd@access.digex.net) wrote:

> Hopefully, the local phone companies will reprogram their switches 
to
> allow dialing of 1 + 500 and 0 + 500 calls.  If they do not, it is 
my
> assumption that calls can still be made via +1.800.CALL.ATT (though
> this is PURELY speculation).

Hopefully, INDEED!  Rochester Telephone never upgraded their switches
to allow for EasyReach service, and I _COULDN'T_ complete the calls
through AT&T's 800 numbers either, as of the summer of '93.  An AT&T
rep told me that they couldn't force local phone companies to upgrade
their hardware/software to handle new LD services, and they also had
the same problem in Cincinnati.  This was one of the many reasons I
cancelled my EasyReach service.


Stan


[TELECOM Digest Editor's Note: Well I am sure Ameritech will be making
all the needed adjustments very soon now since they are also entering
the 500 arena. According to the {Chicago Sun Times} on Thursday, 
Ameritech
has been given approval to offer their own 500 numbers for local and
long distance use. As to be expected, AT&T and MCI both screamed 
loudly
to protest, claiming Ameritech would favor itself in the form of 
reduced
access rates (charged to its own telcos on its books) as opposed to 
the
access rates it has already demanded from AT&T and other long distance
carriers who intend to offer this service. So I don't think anyone is
going to have to tell *our* telephone company here about it ... grin.

Not only that, Ameritech's version is going to have a prefix for 
cellular
customers where the caller pays for the airtime instead of the 
traditional
method where the cellular owner pays in both directions. They are 
going to
offer voicemail, transfer on busy/no answer and a few other goodies on
their version as well, and this has gotten AT&T all the more annoyed 
according to the newspaper account.   PAT]

------------------------------

From: Jerry Eckler <jeck@onramp.net>
Subject: Re: Newbridge Channel Bank
Date: 29 Dec 1994 17:38:45 GMT
Organization: On-Ramp; Individual Internet Connections


tague@cwinc.win.net (Michael Tague) wrote:

> where is the Newbridge company located (or phone number)?

The listing in the new Dallas Yellow Pages shows the following:

   Newbridge Network, Inc.
    14275 Midway Rd.
    I am not sure if this is Dallas or Addison, Texas
    (214) 490-4200

I think this is the home office.  If not they should be able to give
you the number.


Hope this helps.

Jerry

------------------------------

From: anadigi@cerfnet.com (William J. Dawson)
Subject: Re: Newbridge Channel Bank
Date: 29 Dec 1994 21:45:02 GMT
Organization: Anadigicom Corporation


In article <telecom14.470.2@eecs.nwu.edu>, tague@cwinc.win.net says:

> Could someone suggest a good -- inexpensive -- place to get a
> Newbridge channel bank.  Also, where is the Newbridge company 
located
> (or phone number)?

> Does anyone have any thoughts about the most cost effective channel
> bank to get -- for voice use.
>
 Our organization manufactures the Channel Bank Multiplexer,
Model MUX100-1 which might meet your requirements.  The MUX100-1
supports various voice interfaces such as 4-wire E&M, 2 wire FXS or
FXO, etc. and converts them into either a T1 or E1 interface.  The
MUX100-1 can be configured to operate from either -48vdc or 115/230VAC
nominal input power.  Data ports are also available although you did
not specify this requirement.  The MUX100-1 can also be configured for
signaling conversion should you require this.

 If you need additional information, please respond via email
anadigi@cerfnet.com or to the below with your requirements:

 Anadigicom Corporation
 Ph-703-803-0400
 Fax-703-803-2956
 Attn: Gene Delancey

------------------------------

End of TELECOM Digest V14 #471
******************************

              
