Re: DATACENTER: Pictures of practical, neat, and scalable cable systems

[Sam Etler <etler@cs.wisc.edu>]

>     The basic idea was to use connectorized 25 pair cat five cabling
> in a star configuration to each equipment rack.  If you have large

We have this with cat three cabling.  Basically we have 25 pair trunks
going to various general places in the machine room from 66 or 110 blocks
in one central location.  Unfortunately, it's Category 3, so no
100BaseTX for us there.  It was a good idea but for some reason we never
extended that to Category 5.  We also do stuff like RS232 over UTP, but
we've pretty much stuck with separate Category 5 runs there too.  It would
be nice to do the same with Cat 5, but the amount of cable that's already
in place sort of makes it pointless for us.  Ah well.

>     In the machine room I spec'd this idea out for, we were carrying
> 10/10 ethernet, PRIs, RS232, RS422, and several other signaling types
> over the existing twisted pair.  For this project I had tested out
> signalling robustness for carrying all of the above on the same cable
> bundle.

I'd be interested in seeing the results from this.  I've always been a
little wary of mixing signal types on wires in close proximity.  I don't
have any good justification for this though and I could be totally wrong.
I've also wondered about problems like crosstalk on things like 25 pair
Cat 5 cables.  I suppose it can't be too big of a problem since people
seem to use them.

One thing I have wondered about, and maybe people have had experiences
with this.. In some of our older 4 pair Cat 3 wiring, we use the two
standard pairs for 10BaseT and then use the regularly unused other pairs
for another 10BaseT link.  This works really well for offices when there
are a shortage of jacks.  What I've wondered and haven't had time to play
around with is if this would work with 100BaseTX and Cat 5.  Something
tells me that there would be some sort of cross talk issues, even if it
was one 100BaseTX with one 10BaseT.  But I'm not an Electrical Engineer or
anything so I can't really justify this thought either.

Sorry if that's a bit off topic for this list.  Email privately if you
think it is.

Sam Etler
UW Madison
CSL Networking