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James Knott
Guest
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 Posted:
Sun Dec 05, 2004 6:21 pm Post subject:
Re: Cable ends: how important is standard? |
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Watson A.Name - "Watt Sun, the Dark Remover" wrote:
| Quote: | You don't have to follow the standard, so long as you use correct
pairing.
As how far your cable would work, is anyone's guess. Also, the
problem is
not inductance, it's the lack of shielding and the unbalance caused by
mixing pairs that causes problems.
There is no shielding with UTP, that's what U stands for - unshielded.
It's not unbalance, it's crosstalk between the transmit and receive
pairs. When pairs are split, the crosstalk is, well, it's intolerable.
|
What do you think is the cause of crosstalk, between the pairs? A twisted
pair, even when used in an unbalanced circuit, provides a significant
amount of shielding, though not as much as an overall contiuous cover
shield, such as you'd find in coaxial cable. When a pair is twisted, there
is that shielding behaviour at work, along with the rejection of common
mode signals, in balanced circuits.
Transmission lines are a very complex topic, which most people have not
studied. I have. |
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James Knott
Guest
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| Posted:
Sun Dec 05, 2004 6:22 pm Post subject:
Re: Cable ends: how important is standard? |
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dg wrote:
| Quote: | Weird huh? When I was first introduced to twisted pair data cabling I
couldn't understand why it mattered and you couldn't just use straight
through termination. Keeps some of us employed!
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For the reasons, read up on transmission line theory. Some amateur radio
books are a good resource for beginners. |
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Dmitri(Cabling-Design.com
Guest
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| Posted:
Mon Dec 06, 2004 7:02 am Post subject:
Re: Cable ends: how important is standard? |
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Newbie wrote:
| Quote: | I note that if you don't follow the 568A/B standard and just connect
the
pins according to matching colors, straight thru, then a cable will
work.
If it's short, anyway. How long would you think that a CAT5e cable need
to
be before the failure to follow the standard would cause so much
inductance
that the cable might fail? I'm wondering if a 50-meter cable might fail
for
that reason. A network cable tester confirms signals on each connector,
but
NIC cards don't recognize it. It's not wired according to standard.
(Don't
ask me why: it's a long story I don't fully understand myself.) Thx.
|
A 50-meter cable WILL fail for that reason. The pin layout is important,
and not just because cabling standards guys said so. The NIC cards and its
hub/switch counterpart port are designed to expect a balanced signal to
come out of the transmitter and come into the receiver. Even the RJ45 jack
inside the NIC card is not just a jack these days but a pretty complex
part with impedance matching transformers inside, and the end of the coils
are connected to the particular pins of the jack, and it is expected that
both conductors of a twisted pair will connect to a particular coil.
So, if you mess around with such basic principals of the signal
transmission, you run a risk of degrading the performance so much that it
would only work within a room or two, and then fail inevitably.
Here is the correct pin layout for your cable repairing pleasure ;-)
http://www.cabling-design.com/references/pinouts/t568ab.shtml
BTW, a not-so-sophisticated cable tester will not pick up the pin layout
problem if all the conductors are wired straight through: it only measures
connectivity between the pins, and not the proper impedance of the circuit
between the pins.
--
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
-------------------------------------
##-----------------------------------------------#
Article posted with Cabling-Design.com Newsgroup Archiv
http://www.cabling-design.com/forum
no-spam read and post WWW interface to your favorite newsgroup -
comp.dcom.cabling - 844 messages and counting
##-----------------------------------------------## |
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Watson A.Name - \"Watt Su
Guest
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| Posted:
Mon Dec 06, 2004 8:04 am Post subject:
Re: Cable ends: how important is standard? |
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"James Knott" <james.knott@rogers.com> wrote in message
news:T5adnaWcK9TVli7cRVn-tg@rogers.com...
| Quote: | Watson A.Name - "Watt Sun, the Dark Remover" wrote:
You don't have to follow the standard, so long as you use correct
pairing.
As how far your cable would work, is anyone's guess. Also, the
problem is
not inductance, it's the lack of shielding and the unbalance caused
by
mixing pairs that causes problems.
There is no shielding with UTP, that's what U stands for -
unshielded.
It's not unbalance, it's crosstalk between the transmit and receive
pairs. When pairs are split, the crosstalk is, well, it's
intolerable.
What do you think is the cause of crosstalk, between the pairs? A
twisted
pair, even when used in an unbalanced circuit, provides a significant
amount of shielding, though not as much as an overall contiuous cover
|
There _is_no_shielding_. You don't seem to understand the concept of a
balanced pair.
| Quote: | shield, such as you'd find in coaxial cable. When a pair is twisted,
there
is that shielding behaviour at work, along with the rejection of
common
mode signals, in balanced circuits.
|
There is NO shielding behavior. The (common mode) interfering signal
can be very high level on both conductors (because there is no
shielding!), but since the interfering signal is _equal_ on both
conductors, there is *no* difference of potential _between_ the
conductors, so there is _no_ transfer of interference to the receiver.
| Quote: | Transmission lines are a very complex topic, which most people have
not
studied. I have.
|
You need to go back and study to learn the basic concept of a balanced
line.
There is _no_ shielding in a UTP cable. |
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glen herrmannsfeldt
Guest
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| Posted:
Mon Dec 06, 2004 8:39 am Post subject:
Re: Cable ends: how important is standard? |
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Newbie wrote:
| Quote: | I note that if you don't follow the 568A/B standard and just connect the
pins according to matching colors, straight thru, then a cable will work.
If it's short, anyway. How long would you think that a CAT5e cable need to
be before the failure to follow the standard would cause so much inductance
that the cable might fail? I'm wondering if a 50-meter cable might fail for
that reason. A network cable tester confirms signals on each connector, but
NIC cards don't recognize it. It's not wired according to standard. (Don't
ask me why: it's a long story I don't fully understand myself.) Thx.
|
My usual numbers are 3m for 10baseT, 0.3m for 100baseTX, and
0.03m for 1000baseT. It depends, though, on exactly which
pairs are mispaired.
-- glen |
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glen herrmannsfeldt
Guest
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| Posted:
Mon Dec 06, 2004 8:40 am Post subject:
Re: Cable ends: how important is standard? |
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James Knott wrote:
(snip)
| Quote: | Inductance is the opposistion to current flow, along a conductor, not the
coupling of signals between adjacent wires.
|
That is self inductance.
| Quote: | There is however, inductive coupling, between conductors,
along with capacitive coupling. The characteristics of the
cable determine both.
|
That is mutual inductance.
-- glen |
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Watson A.Name - \"Watt Su
Guest
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| Posted:
Mon Dec 06, 2004 1:12 pm Post subject:
Re: Cable ends: how important is standard? |
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"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
news:%vQsd.143193$V41.93879@attbi_s52...
| Quote: | Newbie wrote:
I note that if you don't follow the 568A/B standard and just connect
the
pins according to matching colors, straight thru, then a cable will
work.
If it's short, anyway. How long would you think that a CAT5e cable
need to
be before the failure to follow the standard would cause so much
inductance
that the cable might fail? I'm wondering if a 50-meter cable might
fail for
that reason. A network cable tester confirms signals on each
connector, but
NIC cards don't recognize it. It's not wired according to standard.
(Don't
ask me why: it's a long story I don't fully understand myself.) Thx.
My usual numbers are 3m for 10baseT, 0.3m for 100baseTX, and
0.03m for 1000baseT. It depends, though, on exactly which
pairs are mispaired.
|
Oh, gee, you make this mistake so often that you have a usual number for
it? ;-)
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The Chairman
Guest
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| Posted:
Mon Dec 06, 2004 1:52 pm Post subject:
Re: Cable ends: how important is standard? |
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Are either of these the preferred or more up-to-date standard, or are they
interchangable.
Also, do any of you guys have tricks (ala Roy G. Biv for the colors of the
rainbow) to remembering this? I suppose it's not hard if you do dozens a
week, but if you are doing only a few a year it would be helpful.
Thanks. |
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David Lesher
Guest
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| Posted:
Mon Dec 06, 2004 4:39 pm Post subject:
Re: Cable ends: how important is standard? |
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The Chairman <monster@earthlink.net> writes:
As long as you make both ends the same, they are functionally equal. [1]
That said, 95% of the folks use 568B; except some USG contracts still
call for 568A.
| Quote: | Also, do any of you guys have tricks (ala Roy G. Biv for the colors of the
rainbow) to remembering this? I suppose it's not hard if you do dozens a
week, but if you are doing only a few a year it would be helpful.
|
Every jack I have seen in years has the color code on the label;
usually the only confusion is me getting out my reading glasses
to read it.
If you are punching down PLUGS, you need to be "dope-slapped" {in
the words of Click & Clack} as you can buy patch cables cheaper than
make them....and get a better cable.
That said: note that the lay alternates COLOR WHITE COLOR WHITE etc.
[1] Well, almost... since the twists are different rates, the pairs
are different lengths. This is of zero interest since the difference
is so small, EXCEPT to the standards folks working on the latest
NTP protocol. Seems that there, the few nanoseconds of difference
DOES matter.
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433 |
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Robert Redelmeier
Guest
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| Posted:
Mon Dec 06, 2004 9:47 pm Post subject:
Re: Cable ends: how important is standard? |
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David Lesher <wb8foz@panix.com> wrote:
| Quote: | As long as you make both ends the same, they are functionally
equal. [1] That said, 95% of the folks use 568B; except
some USG contracts still call for 568A.
|
The residential std now calls for -A to get USOC compatibility
for pair one (blue) _and_ pair two (orange).
| Quote: | If you are punching down PLUGS, you need to be "dope-slapped"
{in the words of Click & Clack} as you can buy patch cables
cheaper than make them....and get a better cable.
|
_FULLY AGREED_. If you don't know what a split pair is,
nor why it's bad, then you've got no business with crimpers.
| Quote: | That said: note that the lay alternates COLOR WHITE
COLOR WHITE etc.
|
Are you _trying_ to be mean? :) The most common error
(in-order pairs crimped) is also perfectly alternating.
The big problem with crimping is it is counter-intuitive.
| Quote: | [1] Well, almost... since the twists are different rates,
|
Always presuming no split pairs!
-- Robert |
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David Lesher
Guest
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| Posted:
Tue Dec 07, 2004 12:10 am Post subject:
Re: Cable ends: how important is standard? |
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Robert Redelmeier <redelm@ev1.net.invalid> writes:
| Quote: | As long as you make both ends the same, they are functionally
equal. [1] That said, 95% of the folks use 568B; except
some USG contracts still call for 568A.
The residential std now calls for -A to get USOC compatibility
for pair one (blue) _and_ pair two (orange).
|
Sigh; WTH cares if you use OR or GN as the 2nd pair...
| Quote: | That said: note that the lay alternates COLOR WHITE
COLOR WHITE etc.
Are you _trying_ to be mean? :) The most common error
(in-order pairs crimped) is also perfectly alternating.
The big problem with crimping is it is counter-intuitive.
|
True, but it's also he case if you DO follow the rules.
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433 |
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Newbie
Guest
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| Posted:
Tue Dec 07, 2004 7:22 am Post subject:
Re: Cable ends: how important is standard? |
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On Sat, 04 Dec 2004 19:14:20 +0700, Newbie <me@privacy.net> wrote:
| Quote: |
I note that if you don't follow the 568A/B standard and just connect the
pins according to matching colors, straight thru, then a cable will work.
If it's short, anyway. How long would you think that a CAT5e cable need to
be before the failure to follow the standard would cause so much inductance
that the cable might fail? I'm wondering if a 50-meter cable might fail for
that reason. A network cable tester confirms signals on each connector, but
NIC cards don't recognize it. It's not wired according to standard. (Don't
ask me why: it's a long story I don't fully understand myself.) Thx.
|
I'm glad this has led to some interesting and informative discussions.
I rewired the connectors according to 568B and then my 50-meter cable
worked fine. Splitting pairs definitely does lead to failure on longer
cables!
Friend of mine and I were doing this lil' home network and our deal was
that I'd do the computer configs if he did the cables. He'd never done
network connectors, though, just telephone connectors (which is more than
I'd ever done), and he'd assumed that straight thru would be fine :). What
was confusing was that the short cables he did for practice worked OK and
the cheap network cable tester confirmed the current on each pin. So then
owing to the help received here and at alt.comp.hardware, I found out about
the standards etc. and the rest is history.
Well, now I also know that there's lots I'd rather be doing than fixing
connectors. Fortunately I won't be doing them often--if ever again!
Wanna thank everyone for the help. Nice group here. |
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Robert Redelmeier
Guest
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| Posted:
Tue Dec 07, 2004 8:43 am Post subject:
Re: Cable ends: how important is standard? |
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David Lesher <wb8foz@panix.com> wrote:
| Quote: | Sigh; WTH cares if you use OR or GN as the 2nd pair...
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Ma Bell! Go wash your mouth out with soap! :)
-- Robert |
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Phil Partridge
Guest
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| Posted:
Tue Dec 07, 2004 3:50 pm Post subject:
Re: Cable ends: how important is standard? |
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In article <ZKadnRsJI5iQly7cRVn-jw@rogers.com>, James Knott
<james.knott@rogers.com> writes
| Quote: | David Lesher wrote:
The ends of the Ethernet are transformer coupled. What this means
is they can differentiate between common mode and differential
mode noise.
That only applies, if the transformers are connected to balanced circuits.
There are many situations, where they are used with unbalanced circuits.
Twisted pair (10baseT etc.) ethernet is a balanced circuit. Coaxial cable
ethernet (10base2 & 10base5) are unbalanced.
Agreed. Coaxial is unbalanced (lets ignore twinax, which has two central |
conductors).
However, coaxial cable is SCREENED. That is how you can get away with a
length of unbalanced cable/signal not picking up everything in the
neighbourhood. - Its down to the screen.
Even then, it is not always that successful.
Phil Partridge
philp@pebbleGRIT.demon.co.uk
Remove the grit to reply |
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Ed Nielsen
Guest
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| Posted:
Tue Dec 07, 2004 6:44 pm Post subject:
Re: Cable ends: how important is standard? |
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If you terminate the jacks B and the phone guy comes out and adds a 2nd
line, he's going to hook up the orange pair. Then somebody's gonna care.
CIAO!
Ed
David Lesher wrote:
| Quote: | Sigh; WTH cares if you use OR or GN as the 2nd pair...
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