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Stuart Robinson
Guest
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 Posted:
Wed Jan 19, 2005 9:34 am Post subject:
Design of the test for 100baseT Ethernet. |
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This question relates to how carefully the CAT5\TSB67 test was designed to
match the operational requirements of 100baseT at the electronic interface
level.
Is the CAT5 test (as in TSB67) good enough to tell us in that a link
should be functional and reliable on 100baseT ?
There are circumstances where it may be convenient to set up a link
between two 100baseT machines, where that link does not conform to
Category 5 specification.
For instance a 30M long patch cable will easily pass the Cat5\TSB67
channel or basic link test, where the main parameters tested are NEXT and
attenuation.
So whilst a 30M patch cable is clearly NOT Category 5 compliant, what is
the probability that it will be functional as a 100baseT link, 50%, 99%,
99.99% ?
Stuart. |
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Robert Redelmeier
Guest
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| Posted:
Wed Jan 19, 2005 6:47 pm Post subject:
Re: Design of the test for 100baseT Ethernet. |
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Stuart Robinson <Stuartr@nospam.please> wrote:
| Quote: | Is the CAT5 test (as in TSB67) good enough to tell us in
that a link should be functional and reliable on 100baseT ?
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AFAIK, yes!
| Quote: | There are circumstances where it may be convenient to set
up a link between two 100baseT machines, where that link
does not conform to Category 5 specification.
|
Then it may not work.
| Quote: | So whilst a 30M patch cable is clearly NOT Category
5 compliant, what is the probability that it will be
functional as a 100baseT link, 50%, 99%, 99.99% ?
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99.99+% if correctly wired and crimped.
Cat5 is a _functional_ spec. If you can make the electrical
parms, you can make it of barbed wire. The "cat5" label on
cable & components isn't "offical" or ultimately meaningful.
It is mostly a fervent hope (promise) by the mfr that if you
match and install these bits correctly, your link will meet Cat5.
A 100m patch-cord may well pass Cat5, the higher attenuation
of stranded being offset by few impedenced discontinuities
and jacks.
A 30m patch-cord might offend against TIA/EIA-568 Structured
Wiring Standard. But it isn't permanent.
-- Robert |
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Stuart Robinson
Guest
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| Posted:
Thu Jan 20, 2005 8:55 pm Post subject:
Re: Design of the test for 100baseT Ethernet. |
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| Quote: | A 30m patch-cord might offend against TIA/EIA-568 Structured
Wiring Standard. But it isn't permanent.
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True, it is a temporary link, and thus the Cat5 standard does not apply
anyway, and thus is cant break that standard.
Does anyone know which was developed first ?
Was the tech standard defining how 100baseT would work (and its electrical
limits) developed first and then a Cat5 spec developed to match those
parameters ?
Or was Cat5 developed first and 100baseT specified to operate within the
capabilities of the cable ?
Stuart. |
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Guest
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| Posted:
Thu Jan 20, 2005 10:29 pm Post subject:
Re: Design of the test for 100baseT Ethernet. |
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Stuartr@nospam.please (Stuart Robinson) wrote:
| Quote: | So whilst a 30M patch cable is clearly NOT Category 5 compliant
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Why is a 30M patch cord not CAT5 compliant? |
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J. Clarke
Guest
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| Posted:
Thu Jan 20, 2005 10:55 pm Post subject:
Re: Design of the test for 100baseT Ethernet. |
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William P.N. Smith wrote:
| Quote: | Stuartr@nospam.please (Stuart Robinson) wrote:
So whilst a 30M patch cable is clearly NOT Category 5 compliant
Why is a 30M patch cord not CAT5 compliant?
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If one is being picky about the EIA/TIA spec that defines CAT5, the longest
allowable patch cables are IIRC 5 meters. A 30 meter patch cable doesn't
meet the letter of the spec, however if one does a channel test on it it
will pass.
--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net) |
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Dmitri(Cabling-Design.com
Guest
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| Posted:
Fri Jan 21, 2005 5:01 am Post subject:
Re: Design of the test for 100baseT Ethernet. |
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"Stuart Robinson" <Stuartr@nospam.please> wrote in message
news:memo.20050119093420.1308A@srnet.compulink.co.uk...
| Quote: | So whilst a 30M patch cable is clearly NOT Category 5 compliant, what is
the probability that it will be functional as a 100baseT link, 50%, 99%,
99.99% ?
Stuart.
|
You are not designing a life support system around that cord, are you? If
not, then what difference does probability make?
If you are designing a (cabling) system and made a conscious decision to
disregard the known standard, then you are dismissing the factual/empirical
data collected during development of the standard. In this case, if you want
to make sure the system you design will work, you have to do tests yourself
and, after you've done statistically significant number of them, decide if
the design is viable, and what's the probability of failure (not zero!).
If you don't want to go through the trouble of proving the new design, and
use it anyways, you'd have to live with (at best) 50% probability that it
will be functioning.
In many situations in life it is sufficient! So, go for it as long as
someone's life does not depend on it. In this case you better pick a
standard solution thus reducing your probability of failure to xx% (no data
known to me in cabling, but pick any low number ;-))
Good LUCK!
--
Dmitri Abaimov, RCDD
http://www.cabling-design.com
Cabling Forum, color codes, pinouts and other useful online resources for
premises wiring users and professionals
http://www.cabling-design.com/homewiring
Downloadable Residential Cabling Guide |
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Guest
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| Posted:
Fri Jan 21, 2005 5:27 am Post subject:
Re: Design of the test for 100baseT Ethernet. |
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"J. Clarke" <jclarke@nospam.invalid> wrote:
| Quote: | If one is being picky about the EIA/TIA spec that defines CAT5, the longest
allowable patch cables are IIRC 5 meters. A 30 meter patch cable doesn't
meet the letter of the spec, however if one does a channel test on it it
will pass.
|
And will work just fine for 100BaseT, which brings us full circle to
the OP's question. The answer, AFAICT is that if it passes
qualification by a CAT5 tester (even if it's barbed wire) it'll work
just fine with 100BaseT.
I suppose the inverse question might be: Is there a transmission line
that will _pass_ a CAT5 certification that will _not_ work with
100BaseT, and if so what are it's characteristics? |
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J. Clarke
Guest
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| Posted:
Fri Jan 21, 2005 8:02 am Post subject:
Re: Design of the test for 100baseT Ethernet. |
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William P.N. Smith wrote:
| Quote: | "J. Clarke" <jclarke@nospam.invalid> wrote:
If one is being picky about the EIA/TIA spec that defines CAT5, the
longest
allowable patch cables are IIRC 5 meters. A 30 meter patch cable doesn't
meet the letter of the spec, however if one does a channel test on it it
will pass.
And will work just fine for 100BaseT, which brings us full circle to
the OP's question. The answer, AFAICT is that if it passes
qualification by a CAT5 tester (even if it's barbed wire) it'll work
just fine with 100BaseT.
I suppose the inverse question might be: Is there a transmission line
that will _pass_ a CAT5 certification that will _not_ work with
100BaseT, and if so what are it's characteristics?
|
As far as the EIA/TIA spec goes, I believe the channel test is the final
arbiter. But the channel test can't be conducted until the cable is in
place wherever it is going to end up. If a cable passes the channel test
but doesn't carry signal, then something pathological is going on.
--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net) |
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J. Clarke
Guest
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| Posted:
Fri Jan 21, 2005 8:02 am Post subject:
Re: Design of the test for 100baseT Ethernet. |
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Dmitri(Cabling-Design.com) wrote:
| Quote: |
"Stuart Robinson" <Stuartr@nospam.please> wrote in message
news:memo.20050119093420.1308A@srnet.compulink.co.uk...
So whilst a 30M patch cable is clearly NOT Category 5 compliant, what is
the probability that it will be functional as a 100baseT link, 50%, 99%,
99.99% ?
Stuart.
You are not designing a life support system around that cord, are you? If
not, then what difference does probability make?
If you are designing a (cabling) system and made a conscious decision to
disregard the known standard, then you are dismissing the
factual/empirical data collected during development of the standard. In
this case, if you want
to make sure the system you design will work, you have to do tests
yourself and, after you've done statistically significant number of them,
decide if the design is viable, and what's the probability of failure (not
zero!).
If you don't want to go through the trouble of proving the new design, and
use it anyways, you'd have to live with (at best) 50% probability that it
will be functioning.
In many situations in life it is sufficient! So, go for it as long as
someone's life does not depend on it. In this case you better pick a
standard solution thus reducing your probability of failure to xx% (no
data known to me in cabling, but pick any low number ;-))
|
I think you're exaggerating the situation--the limit on patch cable length
in the EIA/TIA spec is put there assuming that the patch cables will be
used in conjunction with a permanently installed cable and two jacks. In
fact ten meters of patch cable are allowed, but broken into two five meter
chunks, and 90 meters of solid cable is allowed in between them along with
two jacks and two plugs and IIRC one cross-connect as well. All in
addition to the plugs at the ends of the channel.
If there is no 90 meters of solid cable and there are no jacks or plugs and
no cross-connect then 30 meters of patch cable will, barring some really
bizarre circumstance, work fine. And such a bizarre circumstance, if it
would selectively prevent 30 meters of patch cable from working but not
prevent ten meters of patch cable, two plugs, two jacks, 20 meters of solid
cable, and a cross-connect from working, be something that I would really
like to see.
--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net) |
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glen herrmannsfeldt
Guest
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| Posted:
Fri Jan 21, 2005 2:42 pm Post subject:
Re: Design of the test for 100baseT Ethernet. |
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J. Clarke wrote:
(snip)
| Quote: | If there is no 90 meters of solid cable and there are no jacks or plugs and
no cross-connect then 30 meters of patch cable will, barring some really
bizarre circumstance, work fine. And such a bizarre circumstance, if it
would selectively prevent 30 meters of patch cable from working but not
prevent ten meters of patch cable, two plugs, two jacks, 20 meters of solid
cable, and a cross-connect from working, be something that I would really
like to see.
|
Yes.
30m of stranded cable should work fine, even 90m. The attenuation
is slightly higher, so you might not want to go to 100m.
There are two standards. The ethernet standard, which Cat 5
satisfies, and tells you what works.
TIA/568 which tells you what works assuming the rest of the
system follows TIA/568. This allows 90m of solid wire, and
two 5m patch cables. You don't have to go measure the 90m
to be sure that a 5m patch cable will work.
Many things that won't satisfy TIA/568 will satisfy ethernet.
Two 100baseTX repeaters more than 5m apart. Even three
100baseTX repeaters if the rest of the cabling is short
enough! Look at the model 2 rules for 100baseTX.
-- glen |
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glen herrmannsfeldt
Guest
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| Posted:
Fri Jan 21, 2005 2:45 pm Post subject:
Re: Design of the test for 100baseT Ethernet. |
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Stuart Robinson wrote:
(snip)
| Quote: | That was rather the reason behind the question, if a link of whatever
makeup passes the Cat5 test, can we be sure to > 99.99% or so that it will
work ?
For instance has anyone ever seen a link pass a Cat5 test but fail in
operation ?
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If you touch the cable, probably not. Maybe 99.5, though.
I have seen too many cables where the connector crimp wasn't
good enough, or for some other reason didn't make contact,
even commercial cables that likely had passed some tests.
Did you include the connectors in the 99.99%?
-- glen |
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Guest
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| Posted:
Fri Jan 21, 2005 7:36 pm Post subject:
Re: Design of the test for 100baseT Ethernet. |
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Stuartr@nospam.please (Stuart Robinson) wrote:
| Quote: | TSB67 only details tests for length, attenuation, NEXT and wire map.
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In terms of a transmission line that you are moving 100BaseT over,
what else matters? |
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Stuart Robinson
Guest
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| Posted:
Sat Jan 22, 2005 9:35 am Post subject:
Re: Design of the test for 100baseT Ethernet. |
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| Quote: | Did you include the connectors in the 99.99%?
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I suppose I meant 99.99%, excluding mechanical failures caused by bad
crimps.
I agree with your point on the crimps though, I have seen many
commercially produced cables that are poorly crimped, but they seem to
work.
On reflection I cant ever recall a 100baseT link failing, but since the
critical point would be at maximum length (greatest attenuation) and most
cables will be well under max length, perhaps thats not surprising.
Stuart. |
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Stuart Robinson
Guest
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| Posted:
Sat Jan 22, 2005 9:35 am Post subject:
Re: Design of the test for 100baseT Ethernet. |
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| Quote: | In terms of a transmission line that you are moving 100BaseT over,
what else matters?
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Not sure, when they incorporated the test into the EIA\TIA 568 spec I
thought they added some other tests.
I dont have a copy of the relevant bit of EIA\TIA 568 (its expensive)
Stuart. |
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