Re: Ethernet connection sensitive to cable length
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Posted by glen herrmannsfeldt on May 4, 2008, 4:09 pm
Please log in for more thread options (snip) Shouldn't that be gato tres? What do they call the wiring in Spain and Mexico? (snip) > (408) 395-5700 Los Gatos, CA 95033
-- glen | ||||
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Posted by DTC on May 4, 2008, 6:39 pm
Please log in for more thread options > What do they call the wiring in Spain and Mexico?
TIA/EIA 583-Ã | ||||
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Posted by msg on May 4, 2008, 2:18 am
Please log in for more thread options Jeff Liebermann wrote:
<snip>
4. In the miscellaneous category...ethernet over 25 pair
> telco bundles
...or perhaps LatticeNet? | ||||
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Posted by Rich Seifert on May 4, 2008, 12:38 pm
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> I once calculated the maximum cable length at about 1,200ft for
> 10baseT-HDX before timing becomes an issue. Why 2,000ft worked is > still a mystery to me. It shouldn't have unless the timing on the > ethernet devices is more relaxed than required. The propagation velocity of UTP is about 5.1 ns/meter, or roughly 1.5 ns/foot. Your 2,000 foot run has a round-trip delay of around 6 us, which is far less than the 48 us allowance in half-duplex 10 Mb/s Ethernet (i.e., 51.2 us less the 3.2 us "jam" time). As long as the *signal characteristics* were still acceptable to the line receiver, it should work, as there are no protocol timing violations in this arrangement. Much of the timing allowance in ordinary networks is allocated to the repeaters; I suspect that your setup was a two-station back-to-back connection, which has LOTS of timing margin. > Also, note that I was
> using 10baseT-HDX (half-duplex). Full duplex and/or 100baseT will not > work due to collision domain issues and cable near end crosstalk. Backwards. The collision domain (timing) issues are related only to *half* duplex Ethernet, not full duplex. You can (and we often do) run full-duplex Ethernet over tens or hundreds of kilometers (using fiber) with no timing concerns. -- 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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Posted by Robert Redelmeier on May 4, 2008, 8:10 pm
Please log in for more thread options > I enjoy asking the original questions backwards. In this
> case, it's "what would I have to do, to CREATE the problem"? A good diagnostic method. > At the time (about 1998), if you purchased any manner of pre-wired
> ethernet jumpers, you got EIA-568B wiring. Never mind that EIA-568A > is the real standard. Well, my accomplice was working on his BICSI > certification, and they were preaching EIA-568A. Probably because the US government requires -A > Never mind that I told him that I wanted the color coding to
> be consistent throughout the entire building, all of which > was EIA-568B. While US industry historically has been -B > Careful here. That's not an endorsement for installing 2,000ft
> CAT5e runs. I once calculated the maximum cable length at > about 1,200ft for 10baseT-HDX before timing becomes an issue. > Why 2,000ft worked is still a mystery to me. It shouldn't have > unless the timing on the ethernet devices is more relaxed than > required. 10basedT has such relaxed timing because of the cascading permitted. It became 100baseTX by tightening the circle. Timing is mostly relevant for collision situations. If you are isolated by a switch, how can it matter? > Also, note that I was using 10baseT-HDX (half-duplex).
> Full duplex and/or 100baseT will not work due to collision > domain issues and cable near end crosstalk. Keeping crosstalk out is probably the main benefit. > As for stretching the technology, I done my part:
I hope these installations have adequate lightening protection! > One of these days, I'll follow the standards and rules,
> but not this week. That's fine when expertise is available for troubleshooting and the reliability is acceptable. -- Robert | ||||
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> office and shot a bobcat who was chasing my house cat, whose name
> happens to be "Cat 3"(he is my third cat). No, I am not planning to
> upgrade him to Cat 5.