Network – Confused about the results from the cable tester

cablingNetworkspeedtesting

A little bit of backstory, just in case you want some context. In the last couple of weeks the network at least internally has slowed down. As far as I can tell the only things that have changed has been new emergency lighting has been installed and some servers have been moved from a different subnet.

Anyway onto the problem / question.

We have a NaviTEK-NT tester and below is an image of one of the network ports results. I have been told the ports should be Cat5e as that is what was requested when the points got installed.What exactly is happening in the image below? As Far as I can tell it's got 2 pairs going 20M, which is about the length of the cable between the network point I use and the patch cabinet. I then have 2 pairs going around 1M, which is maybe the rough length of the Ethernet cables combined (about 0.3/0.4m * 2).

In my head this indicates that maybe their is a break or something as I'd expect 4 pairs of 20M ~ cable length. However as far as the manual is concerned I would see a red line cutting the cable if there was a break.

TLDR:
In the image below why are 2 pairs 20m and the other 2 are 1m in length. What does this indicate? It should be patched up as Cat5e though I wouldn't rule out it being just a cat5.

If I have missed anything let me know and I will try and find out anything else that could help. Thank you very much.

Network Test Results

Best Answer

I offer another interpretation: 4 wire cable for 100Mbit/s.

This is basically the same as zac67's answer "Either it's a bad LSA contact, a bad panel insert or a damaged cable.", but probably the situation is intentional, not accidental.

It is compelling that it's exactly pairs 1/2 and 3/6 that are 20m long, while the other pairs are just shown with the length of the patch cable used to connect the tester to the cable.


EDIT: Actually, the above statement might be wrong.

The cable tester's graphical result is somewhat puzzling. It does show "S" (shielding) as a interrupted link, but the presentation of wire pairs 4&5 and 7&8 is shown as single strech of 1m cable.

If wire pairs 4&5 and 7&8 were discontiguous, i.e. present in the 1m patch cords, but "absent" (probably: "used elsewhere") in the ~20m of fixed-installation cable, they should be shown the same way as the shielding link: with a gap.

Then again, this might be a misinterpretation by the cable tester.


There were days when installed 8-wire cable was used to provide two 8P8C connectors (a.k.a. "RJ45"), but equipped with just 4 wires each (1,2,3,6), to "save some money", and of course because 100Mbit/s Ethernet was a big thing back then and because it ran fine on just two twisted pairs.

Saving money that way has a veeeeery long tail, as we now see. And then there were "Cat5" labelled patch cords too, with just two pairs inside. m-(

You may want to check if you happen to have found one of these old tripwires (pun intended).

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