Re: Ethernet connection sensitive to cable length
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Posted by windsurferLA on May 4, 2008, 12:25 am
Please log in for more thread options Robert Redelmeier wrote: >> windsurferLA wrote:
>>> Location #2 ? WORKS fine when linked by home built 40? long
>>> CAT5 cable. Location #3 ? DOES NOT WORK when linked by home >>> built 100? long CAT5 cable. ? Not only is there no communication >>> over the link, but the lights on both routers do not even >>> indicate a connection. YET, if at this same location #3, the >>> 100? long cable is plugged into any one of several computers, >>> the connection indicator lights come on immediately, and full >>> normal network access is quickly obtained. >
> These homebuilt cables, which wiring pattern did you use? > T-568A or -B ? If you don't know what I'm talking about, > it is highly likely you split a pair. > > Please do not complain "but the other comp works". > Difference NICs and drivers are more error-tolerant > and have more robust fall-backs. > > Electrons may be color blind, but they _do_ know > who their dance [twist] partners are. > > -- Robert > Robert ... thanks for the hint.. the likely cause has been identified. When you asked about T-568A or T-568B, it triggered a memory. I then recalled that the connectors were not assembled at the same time; one end was rebuilt because of intermittent connection problems. The intermittent end had been the very first RJ45 connector that I had ever assembled. I further recalled being uncertain at the time I was rebuilding the connector whether to use the "A" or "B" configuration. Now doubting my wiring skills, I got out my jeweler's eye loop to very carefully look at both ends to make sure one had not be wired "A" and the other "B." The result was not what I expected. A careful examination of the newer end appears to reveal that the blue-white (#5) and the green white (#3) were inadvertently interchanged at that end and only that end. I expect that repairing the cable will solve the problem. WHAT I FIND SURPRISING is that the cable has worked with so many (guest's) computers for so long that it was not until the A - B question was raised that I thought to check the colors of the inner wires - a not so easy a task for old eyes like mine. Obviously, there is enough cross talk between the pairs to effect a connection with most, but not all, hardware. Although I feel rather stupid for not spotting the wiring error earlier, I never suspected a wiring error would be the problem. When ever I assemble a connector, I keep a multi-colored wiring chart right in front of me. Obviously, it was not enough to preclude the error. Thanks for everyone's help.. Tomorrow, we try a rebuild. | ||||
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Posted by Robert Redelmeier on May 4, 2008, 3:22 pm
Please log in for more thread options > When you asked about T-568A or T-568B, it triggered a memory.
That's the idea. > Now doubting my wiring skills, I got out my jeweler's eye
> loop to very carefully look at both ends to make sure one had > not be wired "A" and the other "B." The result was not what > I expected. A careful examination of the newer end appears to > reveal that the blue-white (#5) and the green white (#3) were > inadvertently interchanged at that end and only that end. This is the most common newbie wiring mistake. Swapping the whites turns the layout into side-by-side and splits the green and blue pairs. > I expect that repairing the cable will solve the problem. WHAT
> I FIND SURPRISING is that the cable has worked with so many > (guest's) computers for so long that it was not until the A - > B question was raised that I thought to check the colors of the > inner wires - a not so easy a task for old eyes like mine. It is hard for everybody, and impossible with some cable mrfs where the whites are unmarked (some plenum). > Obviously, there is enough cross talk between the pairs to
> effect a connection with most, but not all, hardware. Crosstalk is not really required. rememeber the signal is differential and also present full-strength on the green. Still, a bit surprising it ran as well as it did. Of course, it never needed to carry more than 1 MBps, so retransmits would go largely unnoticed. > Although I feel rather stupid for not spotting the wiring
> error earlier, I never suspected a wiring error would be > the problem. Many years of experience have led to to _ALWAYS_ check the cabling first. Especially if there is any indication it is home-made. It is incredibly difficult to crimp connectors correctly. -- Robert | ||||
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Posted by DLR on May 6, 2008, 2:30 pm
Please log in for more thread options Robert Redelmeier wrote:
>> When you asked about T-568A or T-568B, it triggered a memory.
>
> That's the idea. > >> Now doubting my wiring skills, I got out my jeweler's eye
>> loop to very carefully look at both ends to make sure one had >> not be wired "A" and the other "B." The result was not what >> I expected. A careful examination of the newer end appears to >> reveal that the blue-white (#5) and the green white (#3) were >> inadvertently interchanged at that end and only that end. >
> This is the most common newbie wiring mistake. Swapping > the whites turns the layout into side-by-side and splits > the green and blue pairs. Which is why I like the Leviton Quick port for the part time do it yourself crowd. You can buy the jacks at Home Depot on Saturday afternoon and they have the wire colors on the sides of the jacks. David | ||||
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Posted by Robert Redelmeier on May 6, 2008, 3:53 pm
Please log in for more thread options > Which is why I like the Leviton Quick port for the part
> time do it yourself crowd. You can buy the jacks at Home > Depot on Saturday afternoon and they have the wire colors > on the sides of the jacks. Agreed. The key is _JACKS_ . They're much easier to get right than _PLUGS_ . -- Robert | ||||
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Posted by DLR on May 6, 2008, 9:53 pm
Please log in for more thread options Robert Redelmeier wrote:
>> Which is why I like the Leviton Quick port for the part
>> time do it yourself crowd. You can buy the jacks at Home >> Depot on Saturday afternoon and they have the wire colors >> on the sides of the jacks. >
> Agreed. The key is _JACKS_ . They're much easier > to get right than _PLUGS_ . I made a patch cord once. Then decided I had the cash to buy them. With hooded and/or snag proof ends no less. At a price that valued my labor at $1 or $2 an hour. | ||||
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