| Author |
Message |
Newbie
Guest
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 Posted:
Sat Dec 04, 2004 5:14 pm Post subject:
Cable ends: how important is standard? |
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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. |
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David Lesher
Guest
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| Posted:
Sat Dec 04, 2004 5:14 pm Post subject:
Re: Cable ends: how important is standard? |
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Newbie <me@privacy.net> writes:
| Quote: | 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?
|
A foot or two...
Fix the terminations -- the wire is paired for very good reasons.
--
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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Sonco
Guest
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| Posted:
Sat Dec 04, 2004 5:42 pm Post subject:
Re: Cable ends: how important is standard? |
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I believe your splitting pairs with straight thru, Pins 1-2 are paired and
pins 3-4 are paired, where it should be pins 3-6 for your second pair.
usefully works at 10mbs and all sorts of problems at 100mbs, regardless of
the length.
"Newbie" <me@privacy.net> wrote in message
news:5u93r0p4cchfkr7ampagd1b5rjkrk0ojaq@4ax.com...
| 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.
|
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David Lesher
Guest
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| Posted:
Sat Dec 04, 2004 8:55 pm Post subject:
Re: Cable ends: how important is standard? |
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James Knott <james.knott@rogers.com> writes:
| Quote: | Newbie 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.
|
It *is* inductance; as well as the imbalance. As correctly configured,
the transmit data is on one pair; the receive data on another.
When you split the pairs, you get a long linear transformer between
the one wire of the {say} transmit pair is now coupled to another
single wire. When that other wire is the receive pair... so instead
of *many* dB of isolation between the transmit and receive pairs;
you get near zero.
--
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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Dr. Anton T. Squeegee
Guest
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| Posted:
Sat Dec 04, 2004 9:17 pm Post subject:
Re: Cable ends: how important is standard? |
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In article <5u93r0p4cchfkr7ampagd1b5rjkrk0ojaq@4ax.com>, me@privacy.net
says...
| 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.
|
<snippety>
Barely. And don't ever expect one wired like that to work at more
than CAT3 (10Base-T) speeds.
Those standards exist for good reason. By wiring as you describe,
instead of wiring to standard, you'll end up splitting the pairs which
is a Really Bad Idea.
If the cables you're dealing with are not wired to standard, then
they should be re-done correctly. Period.
Good luck.
--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
(Known to some as Bruce Lane, ARS KC7GR,
kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
"If Salvador Dali had owned a computer, would it have been equipped
with surreal ports?" |
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David Lesher
Guest
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| Posted:
Sat Dec 04, 2004 11:37 pm Post subject:
Re: Cable ends: how important is standard? |
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James Knott <james.knott@rogers.com> writes:
| Quote: | Inductance is the opposistion to current flow, along a conductor, not the
coupling of signals between adjacent wires. There is however, inductive
coupling, between conductors, along with capacitive coupling. The
characteristics of the cable determine both.
|
No, inductance is the physics effect, for lack of a better label,
that causes "inductive coupling"...
But it's not worth debating definitions. The OP has a choice: punch
down the cable correctly, or not expect it to work.
--
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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James Knott
Guest
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| Posted:
Sat Dec 04, 2004 11:37 pm 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.
|
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. |
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James Knott
Guest
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| Posted:
Sun Dec 05, 2004 2:42 am Post subject:
Re: Cable ends: how important is standard? |
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David Lesher wrote:
| Quote: | James Knott <james.knott@rogers.com> writes:
Newbie 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.
It *is* inductance; as well as the imbalance. As correctly configured,
the transmit data is on one pair; the receive data on another.
When you split the pairs, you get a long linear transformer between
the one wire of the {say} transmit pair is now coupled to another
single wire. When that other wire is the receive pair... so instead
of *many* dB of isolation between the transmit and receive pairs;
you get near zero.
|
Inductance is the opposistion to current flow, along a conductor, not the
coupling of signals between adjacent wires. There is however, inductive
coupling, between conductors, along with capacitive coupling. The
characteristics of the cable determine both. |
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David Lesher
Guest
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| Posted:
Sun Dec 05, 2004 4:48 am Post subject:
Re: Cable ends: how important is standard? |
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The Chairman <monster@earthlink.net> writes:
| Quote: | Since you both seem to know a lot about this, can you explain it to me
in layterms? Basically, from what I knew before I started dealing with
computer networking, a wire is a wire and as long as wire 1 goes to
terminal 1, wire 2 goes to terminal 2, etc. the cable will work. For
instance, this is the case with phone cords.
However, I have been much disabused of this notion lately. So,
basically, in terms for the common man like me, why do the pairs need to
stay together?
|
The ends of the Ethernet are transformer coupled. What this means
is they can differentiate between common mode and differential
mode noise.
If you have 2 parallel wires, say spanning a room, both are antennas,
picking up the noise from {say} the next room. I think you can see
that to the most part, they pick up the SAME noise. That's common_mode
input. But the next receiver stage, what the wires connect to, will
ignore that and only look at the pushme-pullyou difference between
wire 1 and wire 2's potential. That difference comes from whatever
drives the input end of those two wires.
OK, now take those two wires and twist them together into a tightly
pair. This raises the ability of the pair to differentiate between
the outside, common_mode {noise} and the intended pushme-pullyou
signal to the nth degree. Why? "an exercise for the student. [1]
Basically, things cancel far better.
Now, you can (and do...) put another twisted pair right next to the
first one and {esp. if the twist rate is different between the two
pairs} almost zero signal will leak from one to the other. THAT's
your goal, and it's important because the receiver in your Ethernet
card [or switch, or..] must hear the far weaker signal from the far
end over its own transmit signal.
But "split" those pairs, and you have in fact coupled most
of the transmit signal into the receiver... and that's
bad news [tm]...
Does that help?
[1] If you are up to the integral calculus, you can prove this.
I emphasize the "you" in this part...cuz I have long since
forgotten..
--
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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The Chairman
Guest
|
| Posted:
Sun Dec 05, 2004 7:44 am Post subject:
Re: Cable ends: how important is standard? |
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David Lesher <wb8foz@panix.com> wrote in news:cothnv$cm2$1
@reader1.panix.com:
| Quote: | James Knott <james.knott@rogers.com> writes:
Inductance is the opposistion to current flow, along a conductor, not
the
coupling of signals between adjacent wires. There is however,
inductive
coupling, between conductors, along with capacitive coupling. The
characteristics of the cable determine both.
No, inductance is the physics effect, for lack of a better label,
that causes "inductive coupling"...
But it's not worth debating definitions. The OP has a choice: punch
down the cable correctly, or not expect it to work.
|
Hey Guys,
Since you both seem to know a lot about this, can you explain it to me
in layterms? Basically, from what I knew before I started dealing with
computer networking, a wire is a wire and as long as wire 1 goes to
terminal 1, wire 2 goes to terminal 2, etc. the cable will work. For
instance, this is the case with phone cords.
However, I have been much disabused of this notion lately. So,
basically, in terms for the common man like me, why do the pairs need to
stay together?
Thanks. Ryan |
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Watson A.Name - \"Watt Su
Guest
|
| Posted:
Sun Dec 05, 2004 10:39 am Post subject:
Re: Cable ends: how important is standard? |
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|
"James Knott" <james.knott@rogers.com> wrote in message
news:Q9CdnYq6Brxmni_cRVn-jA@rogers.com...
| 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.
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. |
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dg
Guest
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| Posted:
Sun Dec 05, 2004 10:46 am Post subject:
Re: Cable ends: how important is standard? |
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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!
--Dan
"Newbie" <me@privacy.net> wrote in message
news:5u93r0p4cchfkr7ampagd1b5rjkrk0ojaq@4ax.com...
| 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.
|
|
|
| Back to top |
|
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Watson A.Name - \"Watt Su
Guest
|
| Posted:
Sun Dec 05, 2004 5:07 pm Post subject:
Re: Cable ends: how important is standard? |
|
|
"The Chairman" <monster@earthlink.net> wrote in message
news:Xns95B5BEEB88E70monsterearthlinknet@140.99.99.130...
| Quote: | David Lesher <wb8foz@panix.com> wrote in news:cothnv$cm2$1
@reader1.panix.com:
James Knott <james.knott@rogers.com> writes:
Inductance is the opposistion to current flow, along a conductor,
not
the
coupling of signals between adjacent wires. There is however,
inductive
coupling, between conductors, along with capacitive coupling. The
characteristics of the cable determine both.
No, inductance is the physics effect, for lack of a better label,
that causes "inductive coupling"...
But it's not worth debating definitions. The OP has a choice: punch
down the cable correctly, or not expect it to work.
Hey Guys,
Since you both seem to know a lot about this, can you explain it to me
in layterms? Basically, from what I knew before I started dealing with
computer networking, a wire is a wire and as long as wire 1 goes to
terminal 1, wire 2 goes to terminal 2, etc. the cable will work. For
instance, this is the case with phone cords.
However, I have been much disabused of this notion lately. So,
basically, in terms for the common man like me, why do the pairs need
to
stay together?
Thanks. Ryan
|
Most NICS (network interface cards) have transformers that have windings
that drive the line and receive the signla from the far end. The
winding is like a see-saw in that there must be a difference in the
voltage on the ends to have a current flow, like if both ends of the
see-saw are pushed down equally, there is no movement.
An interfering signal that affects the twisted pair line affects both
conductors equally so there is no difference between the conductors, and
there is no current flow in the winding, and no interference gets thru
the transformer. If you have one conductor 'different' i.e. longer or
shorter, or if it's mixed with another pair, then there is a difference
and the current flows in the transformer winding, and interference gets
thru.
The RS-232 signals were each on a single conductor, relative to the
ground. The data rates were slow, and the voltages were high so any
interference didn't affect the signal enough to cause errors. But as
data rates increased, the world needed a better system, so the RS-422
standard with balanced pairs was developed. This allowed the data rate
to be increased orders of magnitude from ten thousand to a million bits
per second.
But ethernet over twisted pair is still much faster than this, so the
balanced pairs are even more critical to maintaining good signal to
noise ratio. |
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James Knott
Guest
|
| Posted:
Sun Dec 05, 2004 6:12 pm Post subject:
Re: Cable ends: how important is standard? |
|
|
The Chairman wrote:
| Quote: | Since you both seem to know a lot about this, can you explain it to me
in layterms? Basically, from what I knew before I started dealing with
computer networking, a wire is a wire and as long as wire 1 goes to
terminal 1, wire 2 goes to terminal 2, etc. the cable will work. For
instance, this is the case with phone cords.
However, I have been much disabused of this notion lately. So,
basically, in terms for the common man like me, why do the pairs need to
stay together?
|
That's a *BIG* topic. However, the idea is that a single wire can act as an
antenna, radiating to and picking up signals from other wires. If two
wires are twisted together, and used in a balanced circuit, the current in
the two wires cancel out the antenna effect, so that they're less likely to
suseptible to interference and also less likely to create interference.
A balanced circuit, is one where neither conductor is grounded. An
unbalanced circuit, is one where one side of the circuit is tied to ground
and often uses coaxial cables, such as those used for cable TV.
You might want to read up on transmission lines. A good reference for
beginners, is "The Handbook for Radio Amateurs", published by the American
Radio Relay League. These books are in many public libraries. |
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James Knott
Guest
|
| Posted:
Sun Dec 05, 2004 6:15 pm Post subject:
Re: Cable ends: how important is standard? |
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David Lesher wrote:
| Quote: | 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. |
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