[Tfug] CAT5 Cables, The Sequel

[Bexley Hall]

Hi, George,

--- George Cohn <gwcohn at simplybits.net> wrote:

> > In the order listed (above).
> > IIRC, pairs were red-green, black-yellow,
> > blue-orange and gr[ea]y-brown
> 
> Those are standard telecom colors, not data colors.

<shrug>  I don't think the cable manufacturer
ever intended for anyone to ever *see* the colors
of the pairs inside their cables!  :>
 
> In a typical analog phone, the red-green pair is
> ring and tip, the 
> connection to the central office or PBX.
> 
> In the old days of mechanical 1A2 multiple line
> phone sets, the 
> red-green pair was voice, the black-yellow pair was
> control for the hold 

IIRC, on pay telephones, ages ago, you could ground
one of the yel-blk pair to get a dial tone.  But,
that may just have been on the "out in the sticks"
exchanges where I lived (dunno, its been many years
since I did any phreaking)

> mechanism, the white-blue pair was the lamp, and the
> grey-brown pair was 
> often used for signaling like the buzzer or bell. 
> If a mechanical phone 
> had more than one line, they went with 25 pair
> cable.  On the old 10 
> button sets, all 25 pairs were used and some ground
> pairs were shared!

Have a 50' length of 25pair you can part with?  :>
(need to run all the pairs from one set of punch-down
blocks to another set on the other side of the house)
 
> Digital phones (not VOIP) also use the red green
> pair and occasionally 
> the black yellow pair depending on the manufacture. 
> Older Nortel SL-1 
> sets used those two pairs but the later digital sets
> used only the 
> red-green pair and power was phantomed over the
> red-green pair.
> 
> I have used 8 conductor flat ribbon telecom wire to
> connect a CSU to a 
> T1 NIU but I try to keep the length short, IE: 7
> feet or less.  A T1 has 
> a bandwidth of 1.54 mb, somewhat less than a 100 meg
> or 1 gig data 
> cable.  Real T1 cable is two twisted pairs with a
> heavy string in each 
> pair and between them to reduce cross talk. Using
> standard cat 3 cable, 
> the telco had to put a digital repeater every 6,000
> feet for a T1 circuit.
> 
> Cat 5 or greater cable has better insulation and the
> pairs are twisted 
> to reduce cross talk at data's higher speeds.  You
> can get away with 
> using cat 3 telecom wire sometimes but it depends on
> the length and what 
> is nearby.  Cables are relatively inexpensive
> compared to other hardware 
> and the cost of data loss until you have to pay to
> have them replaced. 

Exactly.

> It's better to err on the side of better quality
> cables initially than 
> have to waste a lot of time troubleshooting flaky
> problems.

In my case, all the cabling (that I am talking about)
is exposed.  The stuff in the walls is already
nailed down.
 
> There are classes in proper Cat 5 and higher wiring
> as well as industry 
> certifications for folks who do it on a daily basis.
> Things like how 
> tightly a bundle of cables can be grouped and not
> running them over 
> florescent light fixtures. It doesn't sound as

Or next to phone lines.

> glamorous as an analyst 
> or programmer but in the over all scheme of things,
> it's just as important.  ;-)

<grin>  I recall having to manually twist conductors
(3 twists per inch) when doing high speed ECL designs.
More "art" than "science".

> We used to have a saying in the telecom industry,
> "If they touch, they 
> talk."  That worked at analog speeds but once things
> went digital, 
> cabling became a serious issue.  Why do you think
> some areas still can't 
> get DSL?  It's because a lot of the old cable in the
> ground won't 
> support the relatively meager 1.5 mb speed!  To get

Exactly.  And, if you have any ground water
infiltration of the cables, the problem gets
even worse (imbalances, etc.)

> around this, the 
> telco has to run fiber to DSLAMS and multiplex the
> data onto the voice pair for the "last mile."
> 
> I was certainly glad when fiber became relatively
> inexpensive as it 
> allowed us to replace a lot of old, slow copper and
> microwave with a 
> more reliable medium that was less affected by
> lightning and ground 
> loops.  Where I used to work, we had a dual
> redundant OC-48 (2.5 gig) 
> Sonet ring backbone between three facilities in
> Tucson.  Even that is 
> relatively slow now, especially when you are sending
> digital images all over the network.

All that free porn!  :>

> http://en.wikipedia.org/wiki/OC-192
> 
> Sorry to ramble on and get OT, my 3+ decades of
> working in the telco and IT industries made me
> do it!  ;-)

I think, nowadays, folks see everything as it was
ALWAYS that way.  I can recall arguing with friends
about the virtues of having to dial "1" to call
"out of town"  :<

--don


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