[Tfug] CAT5 Cables, The Sequel

[George Cohn]

> 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.

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 
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!

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

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

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 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.

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!  ;-)

George Cohn