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#11
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Opticreep wrote:
But that still doesn't make sense. I don't think the signal-to-noise ratio should be affected so drastically from this one little mistake. What you think has no bearing on physics. Mispairing the signals eliminates essentially *all* of the noise immunity that's designed in to Cat5 cables. This is undoubtedly the source of your problem and why we always recommend buying commercially manufactured patch cables rather than making them yourself (or having a friend make them). And besides, why would this 24-ft CAT5e cable work between a DSL straight to my PC, but *not* work between a router and a PC? Maybe it has to do with signal strength or the different impedences, but thinking too much makes my head hurt. More likely it's because your DSL modem only supports 10BaseT, so your PC to DSL modem connection is only running at 10Mb whereas the router and your PC probably both support 100BaseTX and thus are trying (unsuccessfully) to run at 100Mb when they're connected together. -Larry Jones I hate it when they look at me that way. -- Calvin |
#12
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Rick Wintjen wrote in message om...
The router probably has a 10/100 interface, also your NIC, so they would have tried to operate at 100T. The modem is almost certainly a 10T. Mis-matched pairs are tolerated better at the lower speeds, but you may have had data errors that weren't bad enough to get your attention. I switched around the mismatched pairs, and now the problem is gone Thanks to everyone for their help. |
#13
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The speed setting at your computer and router should match are at the best
be set to Auto. Mismatch speeds usually don't work well at all. wrote in message ... Opticreep wrote: But that still doesn't make sense. I don't think the signal-to-noise ratio should be affected so drastically from this one little mistake. What you think has no bearing on physics. Mispairing the signals eliminates essentially *all* of the noise immunity that's designed in to Cat5 cables. This is undoubtedly the source of your problem and why we always recommend buying commercially manufactured patch cables rather than making them yourself (or having a friend make them). And besides, why would this 24-ft CAT5e cable work between a DSL straight to my PC, but *not* work between a router and a PC? Maybe it has to do with signal strength or the different impedences, but thinking too much makes my head hurt. More likely it's because your DSL modem only supports 10BaseT, so your PC to DSL modem connection is only running at 10Mb whereas the router and your PC probably both support 100BaseTX and thus are trying (unsuccessfully) to run at 100Mb when they're connected together. -Larry Jones I hate it when they look at me that way. -- Calvin |
#14
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Opticreep wrote:
(snip) It's straight-through. Although I may have a weird theory on why I'm having problems. Apparently, my CAT5 cables weren't properly made. I noticed that pins 3 & 6 on the RJ45 didn't make a twisted pair. Instead, the techie who installed the RJ45's for me made twisted pairs out of pins 3 & 4, and then 5 & 6. This probably generated a lot of noise on signals going through pins 3 and 6. I'm quite sure that category 5 standards state that pins 3 & 6 make up a pair (and so does 4 & 5). It isn't so much signal to noise, but the signal couples to the other wires. Depending on which wires, it can make a big difference in the signal at the other end. This oversight probably didn't affect my short 0.5 meter cables too much. But on a 25-meter cable, the signal-to-noise ratio might have become too high. At least that's my theory. But that still doesn't make sense. I don't think the signal-to-noise ratio should be affected so drastically from this one little mistake. And besides, why would this 24-ft CAT5e cable work between a DSL straight to my PC, but *not* work between a router and a PC? Maybe it has to do with signal strength or the different impedences, but thinking too much makes my head hurt. All routers I know of have 10baseT input and 10/100 output. That makes a big difference in how well the cable works if mispaired. -- glen |
#15
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glen herrmannsfeldt wrote:
It isn't so much signal to noise, but the signal couples to the other wires. Depending on which wires, it can make a big difference in the signal at the other end. Anything other than the desired signal is noise. Therefor signal from the other wires is noise. There's even a word for that type of noise. It's called crosstalk. -- Fundamentalism is fundamentally wrong. To reply to this message, replace everything to the left of "@" with james.knott. |
#16
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James Knott wrote:
glen herrmannsfeldt wrote: It isn't so much signal to noise, but the signal couples to the other wires. Depending on which wires, it can make a big difference in the signal at the other end. Anything other than the desired signal is noise. Therefor signal from the other wires is noise. There's even a word for that type of noise. It's called crosstalk. Well, it is, but neither describes this case so well. If you pair on (3,4) and (5,6) for 100baseTX the (3,6) signal will couple to wires 4 and 5. Most likely the result is that there isn't enough signal left at the end, even without any noise. The receiver requires a certain amount of signal, independent of the amount of noise actually present. Depending on the arrangement of the pairs in the cable, some will couple as common mode signals onto other pairs, again lost to the intended receiver. For a different example, if you manage to pair (1,3) and (2,6) the signal will then couple between the active signaling pairs. Though even in this case it should be absorbed by the terminating resistors on the transmitter and not affect the receiver much (for 100baseTX). Now for gigabit, where all four pairs are used in both directions, any coupling goes directly into the receiver of the wrong pair. I don't believe that the OP is using gigabit, though. -- glen |
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