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I have somewhat successfully installed Cat5e cabling in my home, which works flawlessly for 10 and 100 Mbit/s, but I am experiencing severe packets loss at Gigabit speeds, on all of the eight cables. So obviously I must have done something wrong.

I've already verified that all connections have 1:1 mapping (all jacks are wired as T568A) and all pins are connected, using cheap testing equipment.

The obvious next step would be renting the expensive kind of testing device, but I wonder if there is either something obvious that I might have missed here, or that I could try with a modicum of skill and an oscilloscope.

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You may have checked for continuity, but have you checked for shorts? Check at each end, between each pin and all the other pins. Cables have been known to be crushed which causes shorts. – Martin Feb 22 '11 at 17:52
@Martin I would imagine that 1:1 means that 1 pin goes to 1 pin and not more then that. – Kellenjb Feb 22 '11 at 18:05
@Martin: If there was a short, the I doubt he would even get 10/100Mbps, and even a cheap tester would pick that up. – BG100 Feb 22 '11 at 22:39
@BG100 - 10/100 only uses two of the four wire pairs, so a short may not affect the behavior at 10/100. – Connor Wolf Feb 22 '11 at 22:51
@Fake Name: Ok, my mistake. – BG100 Feb 23 '11 at 8:04

As you increase in speed the quality of the construction and length of the cable makes a big difference. CAT5E can support Gigabit speeds, but only when constructed at high quality. While CAT6 can have a slightly poorer construction and still work.

The main thing I would check is how much of the twisted pair you have untwisted. You should have none except for what is in the slots of the connector.

The other things to check is to make sure that your connector is actually rated as CAT5e. Just because your cable is CAT5e doesn't mean your plugs are.

Do you have access to CAT6 connectors? If so try putting them on your CAT5e cable and see if you get improved performance. The CAT6 connectors are designed for a slightly thicker cable, which is not ideal for your situation, but may help you get the untwisted part to be less.

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Most likely not twisted far enough up to the connector. I've not seen hardly any issues from the connectors themselves. In nearly every case it's been untwisting too far back. Second most likely is not having all the wires pushed in far enough. It's common for people to only get the wire pushed far enough for the first half of the vampire tap to make a connection, leaving the second half unconnected. – Brian Knoblauch Feb 22 '11 at 18:29
That sounds like it could be the problem -- although I'm still puzzled that all cables I made seem to have the same issue, regardless of length. – Simon Richter Feb 23 '11 at 12:52
any kinks or sharp bends (90 degree) in cat 5E will also be a major problem at gigabit speeds. You mentioned jacks, if you mean wall jacks make sure you haven't coiled/kinked up extra wire behind the jack and that you didn't use a staple gun directly on the wire, pinching it. In generally cat-5e is quite sensitive when running at gigabit speeds. – Mark Feb 23 '11 at 21:20

Gigabit needs all 4 pairs, 10/100 uses only two. If you hadn't connected all 4 pairs, it wouldn't have worked all. Since yours is working at Gigabit but with a high error rate, this is not your problem. But others finding this question might have that, so that's why I answered.

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Outside of a faulty connection or poor quality cable, I have found the most common cause of the types of packet loss you describe, is interference from electrical devices. The most notorious is of course, the fluorescent light. Other common contributors are the ambiguous AC adapters (wall warts) often found powering computer and network gear, including the switch your cable probably connects to. My advice is to trace each cable route and ensure there are no electrical devices near the cables. This doesn't necessarily require any tools, but it is a good step to follow in verifying your Cat5e cable installation.

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"ambiguous AC adapters" - do you mean ubiquitous or anonymous? – Martin Feb 23 '11 at 9:24
@Martin - good question. I called them ambiguous because they all seem to look alike and unless they are labeled (pet peeve) it's very difficult to tell what they are powering. So, at least in MHO, they are "ambiguous - their meaning/use is not well defined. Probably not the best use of the word, but it seemed to fit with my experience. Ubiquitous would certainly fit too, but for a different reason. Thanks for reading closely enough to question that! :) – TMarshall Feb 23 '11 at 16:52

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