[sdiy] question about cables

[Jerry Gray-Eskue]

True the majority of connections inside the CO are wire wrap, the punch down
blocks are most extensively used outside the plant in pedestals and
cabinets. Don't forget about all the large IDC connectors used for equipment
hookup (not used to reroute individual pairs). The Matching of the pairs is
by manufacturing specifications, a small mismatch ( feet) in length is no
big deal. Each pair is however color coded and it is bad form to mix tip and
ring across pairs. As you say the twist is only a few turns per foot.

- Jerry

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Cary Roberts
Sent: Monday, August 24, 2009 11:47 AM
To: synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] question about cables


>The telephone systems are designed and built using matched solid
>wire twisted pairs throughout the system.

I've never heard the term "matched" or "twisted pair" when referring to
copper in a physical plant, inside or out.  POTS and T1 circuits are at best
on CAT3 which has three twists per foot.  There is a mix of 22, 24, and
26AWG in every CO I've been in.  For voice, DSL, and T1 I've seen no regard
for matching length of tip and ring.

>They do make extensive use of insulation displacement connections
>in punch down blocks and other connector types.

Very few offices use punchdown.  Most everything is wirewrap including voice
circuits.  Outside plant typically uses IDC for splicing and cross-connects.

>The entire system is designed for reliability and ease of rerouting
>hardwiring, notably a lot of the IDC is reused when wiring changes
>are made without a loss of reliability.

Again, I've seen very little IDC in the central office.  Many CLECs used IDC
but wirewrap and soldered tree terminals still reign in most US incumbent
LEC offices for anything that is frequently moved, added, or changed.

-Cary
(who spent 4+ years running test and install crews for what is now the
largest US telco provider)

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