Subject: [USR-TC] Anyone familiar with Balance and Un-Balanced E1/PRI

From: "Stephen Rivera - WRCA.Net" <[email-masked]>
Date: Mon, 24 Jun 2002 16:31:09 +0000

Customer is asking....(in regards to Dual E1/PRI)
Can you please explain to me whether these should be balanced or
unbalanced?

I'm asking..Is this dictated by Telco? If so, does the card have the ability to
change via software setting or board jumper? Does it even matter to the 
card set?

Steve Rivera  IM: srivera711
Toll Free: (877)WRCANET x102  DIRECT: 732-833-2034
Fax available equipment to: (732)833-2115
for more product info got www.wrca.net

---

From: Jeff Mcadams <[email-masked]>
Date: Mon, 01 Jul 2002 14:18:53 +0000

First off...sorry for the delay in replying to this...was on vacation
last week hiking in Colorado (no, I didn't see any wildfires ;)  Didn't
see any other responses, so hopefully this will help.

Also sprach Stephen Rivera - WRCA.Net
>Can you please explain to me whether these should be balanced or

In general usage, a balanced line is a line where the "signal" (analog
or digital) is sent on two different wires with opposite polarity (ie,
where one has a positive voltage, the other wire will have an equal but
negative voltage).  This gives greater immunity to RF interference and
the like.  Unbalanced, of course, being when it only uses a single wire
for the signal, and the measurement of the signal is measured relative
to ground, thus resulting in less resistance to RF interference.

FWIW, ethernet, and traditional 4-wire T1's are balanced signals (2
transmit wires, 2 receive wires, the polarity of the signals on the 2
wires of each type are opposite of each other).  DSL is *un*balanced (it
only uses 2 wires, so there aren't 4 wires on which to balance the
signals).  I don't know about how E1's work down at the wire level
(being in North America), but I suspect they are balanced.

Also, FWIW (this may be getting into more than you wanted to know), the
balancing of the signals is why you have the twisting in twisted pair
cables.  If the wires ran straight side by side (we'll say left and
right for example), another wire running to the left of the two wires
would induce more signal in the left wire than it would in the right,
and screw up the balanced signal (only slightly, but over long runs, it
can add up).  By twisting the wires together, at one point the other
wire will induce more signal on the first wire, but after the twist, it
will be inducing more signal on the second wire, offsetting the previous
extra induced signal in the first wire...overall this keeps the balanced
signal correct over long hauls.

>I'm asking..Is this dictated by Telco?

Typically, yeah...whatever the interconnect is, is what you'll need to
run, unless you convert it somewhere along the way.  I'd be really
surprised if it wasn't a balanced line as pretty much all T1's on copper
are balanced.

(Note, this whole discussion has to do with copper wiring, you don't get
RF interference from fiber, so the issue is moot there).

>If so, does the card have the ability to change via software setting or
>board jumper? Does it even matter to the card set?

I've not seen any settings to change this, but haven't had the need to
look for it.
-- 
Jeff McAdams                            Email: [email-masked]
Head Network Administrator              Voice: (502) 966-3848
IgLou Internet Services                        (800) 436-4456

---

From: Charles Sprickman <[email-masked]>
Date: Tue, 02 Jul 2002 07:31:50 +0000

I'm pretty sure T1's are NOT balanced.  Think of the tx and rx pairs as
two seperate lines, they aren't necessarily bundled together.  If it was
balanced, you'd see three wires per tx/rx "pair"; you'd have the ground,
positive and negative...  Haven't seen that (yet).  The closest I've seen
is a shielded run...

--
Charles Sprickman
[email-masked]

On Mon, 1 Jul 2002, Jeff Mcadams wrote:

> _______________________________________________
> USR-TC mailing list
> [email-masked]
> http://mailman.xmission.com/cgi-bin/mailman/listinfo/usr-tc
>

---

From: Jeff Mcadams <[email-masked]>
Date: Tue, 02 Jul 2002 12:59:31 +0000

Also sprach Charles Sprickman
>two seperate lines, they aren't necessarily bundled together.  If it
>was balanced, you'd see three wires per tx/rx "pair"; you'd have the
>ground, positive and negative...  Haven't seen that (yet).  The closest
>I've seen is a shielded run...

Being balanced doesn't require a ground.  A ground just means that its
grounded.  Balanced is just having two signals of opposite polarity and
reading the signal as half the voltage differential between the two
wires.  Unbalanced is reading the signal as the differential between the
signal wire (just one) and ground.  Ground, in the unbalanced case, can
be a local ground, there doesn't have to be a ground in the cable to
measure against.  In fact, after a cable run, its likely to *not* have
the same potential as a real ground as there's a good chance that there
will have been current induced in it.
-- 
Jeff McAdams                            Email: [email-masked]
Head Network Administrator              Voice: (502) 966-3848
IgLou Internet Services                        (800) 436-4456