| Author |
Message |
DaveC
Guest
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 Posted:
Wed Apr 27, 2005 4:20 pm Post subject:
10base-T & POTS in same Cat-5 cable? |
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Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are
being used for 10base-T? Wondering about cross-talk, etc., introducing noise
between these two.
Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.
DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group |
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Rick Merrill
Guest
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| Posted:
Wed Apr 27, 2005 9:25 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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DaveC wrote:
| Quote: | Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are
being used for 10base-T? Wondering about cross-talk, etc., introducing noise
between these two.
Thanks,
|
Yes. Make sure you have the right pairs connected to the right terminals
(i.e. follow the specs) |
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Robert Redelmeier
Guest
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| Posted:
Wed Apr 27, 2005 10:07 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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In comp.dcom.cabling DaveC <me@privacy.net> wrote:
| Quote: | Is it acceptable to use 1 pair in a Cat-5 cable for POTS
when 2 pair are being used for 10base-T? Wondering about
cross-talk, etc., introducing noise between these two.
|
Yes, the 10baseT specs were actually designed with this
in mind, although most people try to avoid it.
-- Robert |
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Dmitri(Cabling-Design.com
Guest
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| Posted:
Wed Apr 27, 2005 10:53 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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DaveC wrote:
| Quote: | Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair
are
being used for 10base-T? Wondering about cross-talk, etc., introducing
noise
between these two.
Thanks,
|
Makes it a pain in the neck to wire at both ends since all the termination
equipment is designed with one jack-one cable paradigm in mind. Also makes
it not standard-compliant as you are not supposed to share horizontal
cable between applications, but it will work. As long as you don't mess up
the pinouts on both ends, of course. Make sure you use pair #1 (blue) for
POTS and #2 (orange) and #3 (green) for Ethernet. Creates less confusion
that way.
Good luck!
--
Dmitri Abaimov, RCDD
http://www.cabling-design.com
Cabling Forum, color codes, pinouts and other useful resources for
premises cabling users and pros
http://www.cabling-design.com/homecabling
Residential Cabling Guide
-------------------------------------
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no-spam read and post WWW interface to your favorite newsgroup -
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Floyd L. Davidson
Guest
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| Posted:
Wed Apr 27, 2005 11:03 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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DaveC <me@privacy.net> wrote:
| Quote: | Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are
being used for 10base-T? Wondering about cross-talk, etc., introducing noise
between these two.
|
That is in fact what CAT5 was designed for!
The higher twist (and generally every other characteristic of
twisted pair designed for 10baseT frequencies) makes it a superb
cable for VF frequencies.
The most likely problem is that any kinks or other damage to the
cable would allow cross-talk from ring current on the phone line
to interfere with the 10baseT signal, but obviously that would
be rare, intermittent, and of very short duration to the point
of virtually never being even noticed (unless you have a couple
teenagers using the phone line... :-) .
The most serious problem would be wiring the connectors wrong.
If they are connected just straight across, with pairs on 1 & 2,
3 & 4, and so on, the Ethernet segment will have a crossed pair
using the tip from one pair and the ring from another. That
will guaranteed result in the phone line, and perhaps other
sources of noise, interfering with the Ethernet. On relatively
typical short runs of CAT5 it will still work though, for
10baseT, and may not ever be discovered. The same cable will
not work at all for 100Mbs Ethernet though, so if you move to a
higher speed network that would immediately become critical.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Floyd L. Davidson
Guest
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| Posted:
Thu Apr 28, 2005 12:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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DaveC <me@privacy.net> wrote:
| Quote: | On Wed, 27 Apr 2005 11:03:15 -0700, Floyd L. Davidson wrote
If they are connected just straight across, with pairs on 1 & 2,
3 & 4, and so on, the Ethernet segment will have a crossed pair
using the tip from one pair and the ring from another.
What you're saying is to be sure to correctly wire 1,2,3,6 as Ethernet pairs,
and 4,5 as POTS, and all should go well. Yes?
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.
|
You clearly have not Googled that question! But we can talk
about it anyway... ;-)
There are 8 pairs of pins on an RJ-45 connector, and at least
three different wiring arrangements that are not compatible.
(And given the 10BaseT arrangement, you can use the 4,5 and/or
the 7/8 pins for something other than 10BaseT on the same cable.)
For example, the same connector and CAT5 cable is commonly
used by telecom people for T1 or DSX-1 circuits. A home user
might not ever see that, but these days even small business
users may have T1 or Fractional T1 services, and could even
have a patch panel and therefore have patch cords for it that
are wired for T1's.
Those will not work when used for 10/100BaseT Ethernet.
The typical mistake that a non-aware person makes is just wiring
the Blue/Orange/Green/Brown pairs straight across to pins 1
through 8 in order. As you've noted above, 1 & 2 is one pair
and 3 and 6 are the other for 10BaseT, hence a straight across
cable will put that signal on the Ring of the orange pair and
the Ring of the Green pair, which is called a "split pair".
Since it is not a twisted pair there is a lot of unbalanced
induction into the pairs which is not canceled by the
common-mode operation as expected when using twisted pair cable.
For short runs it will actually work though, at 10Mbps, and
might go undetected if the only test made on the cable is for
continuity. It won't work at all past a few feet for 100Mbps
Ethernet.
Of course if you are are wiring *both* the plugs on the cords
and the jacks, it makes no difference at all as long as they are
done the same. Hence you can wire them for T1's, for 10BaseT,
or just pairs 1 to 4... but then you have to keep all the cords
from getting mixed up too! That problem is already bad enough,
what with crossover and non-crossover already needed for the
10BaseT cords, so even if you don't have T1's you'd still
potentially have 3 types of cords just for 10BaseT.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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DaveC
Guest
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| Posted:
Thu Apr 28, 2005 12:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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| Quote: | What you're saying is to be sure to correctly wire 1,2,3,6 as Ethernet
pairs,
and 4,5 as POTS, and all should go well. Yes?
|
On Wed, 27 Apr 2005 14:09:19 -0700, Floyd L. Davidson wrote
(in article <87vf682agw.fld@barrow.com>):
| Quote: | You clearly have not Googled that question! But we can talk
about it anyway... ;-)
|
Actually I didn't need to; I know the pin-out of 10baseT (see above). Your
answer was not clear to me, so I asked a 1-line clarification question...
| Quote: | And given the 10BaseT arrangement, you can use the 4,5 and/or
the 7/8 pins for something other than 10BaseT on the same cable.
|
....to which the answer is, apparently, "yes". :-)
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.
DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group |
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James Knott
Guest
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| Posted:
Thu Apr 28, 2005 12:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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DaveC wrote:
| Quote: | Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are
being used for 10base-T? Wondering about cross-talk, etc., introducing
noise between these two.
|
Yes, it's entirely acceptable. When twisted pair ethernet was created, it
was intended to be run on existing cat 3 telephone cables, along side phone
lines. Also, the frequencies used on telephones are nowhere near those
used by ethernet, so interference is unlikely. I've even seen
installations, where two 100 Mb ethernet circuits share one cable. |
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James Knott
Guest
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| Posted:
Thu Apr 28, 2005 12:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Robert Redelmeier wrote:
| Quote: | In comp.dcom.cabling DaveC <me@privacy.net> wrote:
Is it acceptable to use 1 pair in a Cat-5 cable for POTS
when 2 pair are being used for 10base-T? Wondering about
cross-talk, etc., introducing noise between these two.
Yes, the 10baseT specs were actually designed with this
in mind, although most people try to avoid it.
|
And of course, it won't work with Gigabit. |
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James Knott
Guest
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| Posted:
Thu Apr 28, 2005 12:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | The most likely problem is that any kinks or other damage to the
cable would allow cross-talk from ring current on the phone line
to interfere with the 10baseT signal, but obviously that would
be rare, intermittent, and of very short duration to the point
of virtually never being even noticed (unless you have a couple
teenagers using the phone line... :-) .
|
Given the great difference in frequencies used, how is cross-talk an issue.
Ringing is generally 20 Hz and voice is less than 4 KHz, whereas ethernet
is up around 5 - 10 MHz (for 10 Mb ethernet). |
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Floyd L. Davidson
Guest
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| Posted:
Thu Apr 28, 2005 12:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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James Knott <james.knott@rogers.com> wrote:
| Quote: | DaveC wrote:
Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are
being used for 10base-T? Wondering about cross-talk, etc., introducing
noise between these two.
Yes, it's entirely acceptable. When twisted pair ethernet was created, it
was intended to be run on existing cat 3 telephone cables, along side phone
lines.
|
I'm not going to look that up to be certain, but I don't think
it is correct. T1 was certainly designed for telephone lines,
but I don't think 10baseT was. Look at the difference in the
twist on CAT5 compared to lesser grade twisted pair!
| Quote: | Also, the frequencies used on telephones are nowhere near those
used by ethernet, so interference is unlikely. I've even seen
installations, where two 100 Mb ethernet circuits share one cable.
|
The frequency has little to do with whether it will interfere.
The voltage level is what makes a difference. Besides, 10baseT
does *not* run at 10Mbps... that is merely the highest bit
rate. The actual frequency spectrum runs from DC on up through
at least 15 Mhz (three times the 5 Mhz fundamental for 10 Mbps).
Which is to say that VF circuits and 10baseT do in fact share
the same frequency range for the entire VF range.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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DaveC
Guest
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| Posted:
Thu Apr 28, 2005 12:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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On Wed, 27 Apr 2005 11:03:15 -0700, Floyd L. Davidson wrote
(in article <87ll743xng.fld@barrow.com>):
| Quote: | If they are connected just straight across, with pairs on 1 & 2,
3 & 4, and so on, the Ethernet segment will have a crossed pair
using the tip from one pair and the ring from another.
|
What you're saying is to be sure to correctly wire 1,2,3,6 as Ethernet pairs,
and 4,5 as POTS, and all should go well. Yes?
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.
DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group |
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Rich Seifert
Guest
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| Posted:
Thu Apr 28, 2005 5:46 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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In article <87r7gv3i1q.fld@barrow.com>,
floyd@barrow.com (Floyd L. Davidson) wrote:
| Quote: | James Knott <james.knott@rogers.com> wrote:
T1 was certainly designed for telephone lines,
but I don't think 10baseT was. Look at the difference in the
twist on CAT5 compared to lesser grade twisted pair!
|
10BASE-T was designed to operate on early Cat-3 UTP wiring. This was
better than untwisted (quad-type) telephone wire, or "silver satin"
modular phone cords. Cat-5 wiring was designed for 100 Mb/s operation.
| Quote: | Besides, 10baseT
does *not* run at 10Mbps... that is merely the highest bit
rate. The actual frequency spectrum runs from DC on up through
at least 15 Mhz (three times the 5 Mhz fundamental for 10 Mbps).
|
Actually, the maximum fundamental frequency for 10BASE-T signals is
10 MHz, not 5.
--
Rich Seifert Networks and Communications Consulting
21885 Bear Creek Way
(408) 395-5700 Los Gatos, CA 95033
(408) 228-0803 FAX
Send replies to: usenet at richseifert dot com |
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Floyd L. Davidson
Guest
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| Posted:
Thu Apr 28, 2005 7:15 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Rich Seifert <usenet@richseifert.com.invalid> wrote:
| Quote: | floyd@barrow.com (Floyd L. Davidson) wrote:
T1 was certainly designed for telephone lines,
but I don't think 10baseT was. Look at the difference in the
twist on CAT5 compared to lesser grade twisted pair!
10BASE-T was designed to operate on early Cat-3 UTP wiring. This was
better than untwisted (quad-type) telephone wire, or "silver satin"
modular phone cords. Cat-5 wiring was designed for 100 Mb/s operation.
|
CAT3 is not "telephone" cable though. Twisted pair telephone
cable is CAT1, useful up to relatively 1 MHz. (A 1.544 Mbps
rate of a T1 has a maximum required frequency bandwidth of 750
KHz, and works just fine on CAT1.)
CAT2 cable was designed for 4Mbps Token Ring and is useful up to
1.5MHz. CAT3 was designed 10Mbps 10baseT, and is useful up to
16 MHz. CAT4 for 20 Mbps (meant for 16Mbps token ring) or
20MHz. CAT5 for 100Mbps 100baseTX and useful up to 100MHz.
The point is still that 10baseT was not designed to work over
telephone cable.
| Quote: | Besides, 10baseT
does *not* run at 10Mbps... that is merely the highest bit
rate. The actual frequency spectrum runs from DC on up through
at least 15 Mhz (three times the 5 Mhz fundamental for 10 Mbps).
Actually, the maximum fundamental frequency for 10BASE-T signals is
10 MHz, not 5.
|
Opps. That's true. It uses Manchester encoding, not NRZ or
AMI. There is either always 1 transition per bit, and sometimes
two. So half the bit rate is the lower frequency limit and the
upper frequency limit is the bit rate (one Hz per bit).
The spectrum used by 10baseT is 5 to 10 MHz. Which makes CAT3
cable a relatively conservative choice... and CAT5 is simply
overkill, but then again I don't even know if anyone stocks CAT3
cable these days!
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Floyd L. Davidson
Guest
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| Posted:
Thu Apr 28, 2005 7:23 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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James Knott <james.knott@rogers.com> wrote:
| Quote: | Floyd L. Davidson wrote:
The most likely problem is that any kinks or other damage to the
cable would allow cross-talk from ring current on the phone line
to interfere with the 10baseT signal, but obviously that would
be rare, intermittent, and of very short duration to the point
of virtually never being even noticed (unless you have a couple
teenagers using the phone line... :-) .
Given the great difference in frequencies used, how is cross-talk an issue.
Ringing is generally 20 Hz and voice is less than 4 KHz, whereas ethernet
is up around 5 - 10 MHz (for 10 Mb ethernet).
|
If the transition period of the eithernet signal happens at a
time when the induced voltage from crosstalk is greater than the
threshold for the ethernet receiver, the receiver will decode an
incorrect value. The significance that frequency plays is just
how often and for how long that effect lasts.
Essentially a 20Hz ring voltage could, for example, wipe out
1/40th of a second worth of 10baseT data if, for example, the
entire positive transition of the ring signal is able to block
the eithernet receiver.
Granted however that the sensitivity to a 20 Hz interfering
signal is going to be significantly less than to a single
frequency that falls inside the spectrum of the desired signal.
But then the voltage level for the ring voltage is huge by
comparison too...
I misspoke about the spectrum of 10baseT ethernet too. You are
right that it is 5 - 10 Mhz, not DC to 5 Mhz (which is what 10
Mbps would be using NRZ encoding).
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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