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'Network cat5 cabling question'
1998\05\11@202222 by Wendall Siemens

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If you get this mail, our network is working! (100M)

-Wendall

-----Original Message-----
From:   john pearson [SMTP:spam_OUTxeroTakeThisOuTspamCWIA.COM]
Sent:   Monday, May 11, 1998 6:26 PM
To:     .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject:        OT: Network cat5 cabling question

Thank you for reading

Is it ok to run 15 to 20 cat5 network cables through about 6' of metal
conduit (1-1/4" emt). I hope this is enough info.

Thank you
John

1998\05\12@104226 by paulb

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Chris Eddy wrote:

> Yes, you are safe.  Cat 5 and other twisted types (twisted pair, not
> mentally) are reasonably good at keeping signals to themselves.  Think
> of phone lines on the pole.

 I'd take this all with a "grain of salt".  Six feet, you should get
away with it.  Some longer distance, maybe fifty feet, you may well
strike problems.

 I'm not actually sure what is meant by "cat 5".  If it refers to
shielded lines, no complaints at all.  If it refers to 10BaseT cabling
using 4 out of an 8-wire cable, then there is a trick as this is *not*
in fact twisted pair.

 Telephone lines on the pole *are* twisted pair as they are carefully
balanced by regular swapping of individual pairs in a pattern (Gray code
variant - it's  abit of a subject in itself); it it to *this* that the
"twist" refers.  Pairs in a composite cable are actually twisted at
different pitches.

 It's all about balancing out "crosstalk".  The flat "strap" cable used
with "RJ" connectors is not twisted pair, and is *not* designed as such
to avoid crosstalk.  Randomly and separately pulled through a duct with
other like cables, it may act "twisted", but if the straps are
accidentally or deliberately laid neatly together for any distance you
really are "asking for" crosstalk problems.

 This is of course exactly what Chris goes on to describe.

 Cheers,
       Paul B.

1998\05\12@223301 by Harold Hallikainen

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On Tue, 12 May 1998 22:17:39 -0000 Eric Smith <ericspamKILLspamBROUHAHA.COM> writes:

>
>Note that flat modular telephone cable is often wired with a flip
>(i.e.,
>pin 1 at one end is wired to pin 'n' at the other end.  10BaseT and
>100BaseT
>cable has to be "straight-through", unless you're using a crossover
>cable
>between two nodes, in which case two pairs get swapped.
>
>


       Anyone know why telephone line cords are assembled with a "flip"?
Actually, the flip SEEMS like it'd be a great idea for data cables.  All
sockets would be wired the same.  The swapping of transmit and receive
pairs would happen in the cable flip.  You could hook anything to
anything (eliminating the old RS232 DTE/DCE problem).


Harold



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1998\05\13@024102 by William Chops Westfield

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   Actually, the flip SEEMS like it'd be a great idea for data cables.
   All sockets would be wired the same.  The swapping of transmit and
   receive pairs would happen in the cable flip.  You could hook anything
   to anything (eliminating the old RS232 DTE/DCE problem).

The last round of "rs232 on rj45" pinouts developed at cisco had exactly
this feature.  You could plug one end of a (flipped) rj45 flat cable into
one jack and the other end into another jack, and the right wires would be
connected so that everything (data, hw flow control, modem control) worked
right.  In addition, the "important" wires were in the middle, so you could
use as small as 4-wire cable for a 3-signal circuit.  I thought it was a
great idea.

It generated quite a bit of complaint and confusion however...

1) Using "standard" wiring schemes, it apparently results in inappropriate
  wires being twisted with each other once you get to the twistewd part
  of the wiring.

2) While we based this and the db25 adaptors on an existing (flipped)
  rj-45 cable assuming that they were "standard", they weren't.  At
  least one entire product line that uses the same pinout for the rj45
  jacks for the "console" and "auxilliary" somehow missed something and
  shipped (for a LONG time) with NON-flipped flat cables, and their own
  (different) rj45-db25 adaptors.  Really confusing things happened if
  you tried to move connectors or cables from those products to or from
  the "terminal server" products that understood the original pinout.

3) Things get confusing when you try to chain cables together...

BillW
cisco

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