Re: [school-discuss] Cat-5 question

[Les Richardson <richl@mail.tfsd.sk.ca>]

Hi Steve,

Great history lesson. Thanks,

Les R.

On Wed, 14 Aug 2002, Tonnesen Steve wrote:

> 
> On Wed, 14 Aug 2002, Mark Evans wrote:
> 
> > A possible alternative is GgOBboNn, but the only
> > time you are likely to see this is on a crossover
> > cable.
> 
> 
> Just as a bit of historical explanation for the strange pairing in CAT5
> wiring:
> 
> 
> 1 2 3 4 5 6 7 8
> G g O B b o N n
> 
> As people have pointed out, the pairs are 12 36 45 and 78.
> 
> The 45 (Bb) pair lines up with the original tip and ring wires used by
> POTS (Plain Old Telephone System) phones.  Note that the 45 pair is still
> right in the center of a CAT5 jack.  You can still plug in a POTS phone in
> a CAT5 jack with a single pair cord and it will work just fine.  This
> system has been used since shortly after farmers used their barbed wire
> fences to talk to their neighbours. 
> 
> Later a data pair was added.  To ensure that old two wire cords could
> still be plugged in, this new pair was added to either side of the
> original tip and ring pair.  The new data pair was used for a second phone
> line, or as a data connection between a PBX phone switch and their
> proprietary telephones.  [SIDENOTE: At the time, the color code used was
> Red and Green for the inside pair and Black and Yellow for the outside
> pair.  You might still see this colour coding on older jacks and cords.]
> 
> When the standard was expanded next, two new pairs were added, one on
> either side of the 4 wire standard.  They couldn't continue the trend of
> putting one wire on either side, because the length required to untwist to
> make a 27 and 18 pair would be too long.  The 8 wire standard is still
> compatible with 2 wire and 4 wire cables. 
> 
> Hope that explains why we have 36 and 45 pairs instead of just 12 34 56
> 78. :)
> 
> 
> Steve Tonnesen
>