cat6 cable only getting 100mbps over larger distance

Question

I know this question has already been asked a few times but I feel that my case is a little different since I've tried all the solutions provided in the other threads.

I created a small diagram to avoid any potential confusion.

So I have a cat6 cable of 80 meters. This cable has worked in the past. However, 2 years later I want to use that cable again and now it only gives me 95 mbps(tested with iperf3), it also gets recognized as a 100mbps link instead of a 1000mbps link. Image 1 provides a visual representation of how everything is laid out at this point.

Parts:

• The lsa wall plug that I use: https://www.allekabels.be/netwerk-wandcontactdoos/11438/1084697/cat6-wandcontactdoos-inbouw.html
• All other ends of the cable are terminated with this rj45 connector: https://www.allekabels.be/stekker-doos-en-krimptang/188/1349725/cat6a7-modulaire-connector.html
• The type of cable I use: S/FTP - CU 250mhz

My troubleshooting steps:

• Redo the connector, router side (changed nothing)
• Redo the lsa wallplug, pc side (changed nothing)
• Test the cable with a cable tester. (all wires are working, but still only 100mbps)
• Check the entire cable for kinks (Found two kinks and cut that piece out. Connected the now 2 cables by adding an rj45 to the ends and connecting them with an ethernet extender, see the after part in the image) (solved nothing)
• Test the cable again with cable tester (all wires are working, still 100 mbps)
• Test the cable with iperf from the router to the extender (950 mbps, recognized as 1000mbps link)
• Test the cable with iperf from the extender to the PC (95 mbps, recognized as 100mbps link)
• (The previous 2 test results do not change if I do them with or without the extender included.)
• Redo the connector for the cable from the extender to the pc (nothing changes)
• Redo the lsa plug for the cable from the extender to the PC (nothing changes).
• Test again with the cable tester (all wires are working)
• Nothing changes no matter what I try.

Things I know for sure:

• The rj45 connectors support solid core cable.
• The lsa plug supports cat6.
• I use the T568B standard everywhere.
• The type of cable I'm using is S/FTP cat6.
• The cable does not run anywhere near any other cables(except where it connects to the router).
• Short distance of about 15 meters works just as it's supposed to.
• Longer distance of about 65 meters gets recognized as a 100 mbps link
• The entire cable runs inside a conduit.

What else could it be?

The only thing I can think of right now is that the signal isn't strong enough by the time It reaches the pc. So I am still planning putting a switch in the middle of the 65 meter part of the cable. However I would rather not do this since this is outdoors and I don't have a good way of protecting the switch or the not interrupted cable from the elements.

If this also does not help, would upgrading to a cat6a help? I read somewhere that cat6 Is not that reliable after about 50 meters.

PS: If you find any spelling/grammar mistakes, please let me know. I am still learning English ;)

UPDATE I fixed the issue by adding a gigabit switch in the middle. Now I have a 1000mbps link with a PC to PC transfer speed of +-870 mbps.

However, there are still a few very interesting answers which you should definitely read if you stumble upon this post in search of a solution to your ethernet problems. Especially the answers from @Zac67 and @The Unix Janitor

Answer 1

Ethernet auto-negotiates using (low-frequency) link pulses. It does not check or train the cable[*1]. Link pulses are exchanged on the two 10/100 pairs and for 1 Gbit/s, all four pairs do an additional link check each.

Some Ethernet devices may fall back to 100 Mbit/s when 1000 Mbit/s has been negotiated but fails to link due to one or two missing pairs - 1 Gbit/s requires all four pairs, 10/100 Mbit/s only use two pairs. This is not by standard though and usually limited to Broadcom chips (they call it Ethernet@Wirespeed). So possibly, one of the pairs in the cable has failed.

Another possibility is that you've mispaired some contacts when terminating the cable. Cheap cable testers cannot detected split pairs as they only check for continuity and shorts. Double check the color codes inside the connectors - you can (but shouldn't) swap entire pairs or the wires within a pair but you must not swap wires across pairs.

While Ethernet over twisted pair is generally limited to 100 m, 90 m of those are required to use somewhat rigid, solid-core cable. Only 10 m are allowed to run over flexible, stranded (patch) cable. Anything beyond that may cause (more or less) errors or fail at any time.

Also, DIY cables for Gigabit Ethernet can very easily exceed the Category 5(e) specification margins and cause transmission errors. You need to make sure that you obey all twisting and pairing rules and generally do a neat job. Connectors must fit the cable (stranded or solid-core) and crimping tools must match the connectors. Buying decent, ready-made cables is very reasonable.

[*1] Notable exceptions to the rule are 2.5GBASE-T and 5GBASE-T aka Smartrate Ethernet. Smartrate ports do train the cable and then link at an appropriate speed between 10GBASE-T and 1000BASE-T, depending on their capability and the cable grade.

Answer 2

You have a lot of variables here:

• To get 1Gbit ethernet you need all 4 pairs of the cable that have no faults and are OFC [Oxygen-Free Copper]; any extenders, joins, or couplers are going degraded the signal (to get 100Mbit, you only need 2 pairs working well).

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A better solution may be to use fiber and a fiber media converter at each end, as it negates the below and is future-proofed (i.e. 10Gbit), while also avoiding all the below since it's non-electrical, more resistant to water damage, easier to work with, and won't be affected by direct or nearby power surges, with the armored types being very hardy.

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Regarding ethernet:

• Do you have a cable tester so you can verify all 4 pairs match at each end and are not being crossed or disconnected?
  • The pairs needed for 1Gbit could be slightly damaged, so test the electrical resistance of each pair or run a known-good cable to rule this out.
  • Do the extenders actually extend all 4 pairs (some cheap ones only do 2)?
• Not all network cards are created equal:
  I've had some network cards/devices be able to go 200m, and upon changing the card out, only 50m; whereas others have better noise filtering and power output, so use a high-quality network card if going for a longer range.
  • Cheap routers can have the worst ethernet ports on them for range and power, as they are designed for the home (20m or less).
  • Try setting each endpoint to 1000Mbit non-auto, as sometimes auto-negotiation to 1000Mbit/s fails due to firmware/software problems, or if there are many errors, it falls back to a slower speed.

UPDATE: (Autonegotiation is a requirement for using 1000BASE-T according to Section 28D.5 Extensions required for Clause40 (1000BASE-T). At least the clock source has to be negotiated, as one endpoint must be master and the other endpoint must be slave." Failed autonegotiation means something is broken )

• You can never rule out interference, even though it's not near anything, as EMF can come from anywhere in the environment.
  • Is the cabled shielded (it should be at that length) and is the shield grounded?
• Every time you terminate the cable or use an extender, breaking and rejoining the cooper, you are adding resistance and attenuation, which is something you're trying to avoid

If this cable runs outside, there are many reasons why this isn't recommended:

• Weather, corrosion, and environmental damage (rodents, wind, electrical storms, etc.)
• EMF from such things as underground powerlines
• If both endpoints are on different power supplies and have different ground paths, they have different potentials, which can cause ground loops, creating interference, and this voltage difference can build-up, damage network equipment, and, in the worse cases, even shock you.

Answer 3

This cable has been outside in the weather. Unless you live in the Atacama Desert, rain water has had a chance to penetrate any slight break in the jacket, such as from a kink, and you could now have water at random locations inside the jacket surrounding the insulated conductors. The water has a higher capacitance than the air that is normally inside the jacket, and this can round-off your square waves and smear your signals enough that the cable won't work at 1000 Mbps.

Do you have access to a vacuum chamber? If you could roll up the cable, stick it in the chamber and maintain a vacuum of about 1 torr or less for a couple of hours, any water inside the jacket should evaporate. If you note a prolonged pause in the pressure drop at 4-5 torr, this is indicative of water leaving the cable, and you should continue pumping down until the pressure remains at or below 1 torr.

If the cable now works at 1000 Mbps for its full length, you should be good until the next time it rains.

Answer 4

Your question says you have an "80 meter" cable, but the evidence you provide suggests you have a 15 meter cable and a 65 meter cable.

If you know the 65 meter cable doesn't work at 1Gbps, adding couplers to the ends of it or attaching the 15 meter cable will not make it better.

As another answer states, if the 65 meter cable has been outside and is not rated for outdoor exposure the jacket may be cracked and been contaminated by moisture.

You should replace the known-broken 65m cable with new wire rated for outdoor use. You may also want to consider replacing this run with optical fiber, especially if the connection is between buildings.

Answer 5

Adding a switch in the middle to boost the signal worked for me. However, I am still only getting +-870 mbps when testing with iperf3 between 2 PC's but that's more than good enough for me.

This is the current layout of everything:

Answer 6

You say the plugs support solid-core cable, which implies you've used solid core cable.

Is there anywhere in the cable path that is unsupported? I've found that any flex at all allows solid core cable to fail internally.

Sometimes people use solid core because its marginally cheaper, and is a lot easier to put into plugs before crimping. This is false economy, and the only time you should use solid core is when the cable is inside a wall/ceiling and will never move.

Solid core wire that is cable-tied to a fence will move as wind pushes the fence about.

Your best option is to replace the one run of solid core cat6 with TWO runs of stranded core cat6. Why two? One for now and one for spare - its only very little more work to run two cables over one cable.

If the run is exposed to weather, you should take the time to run it all inside conduit. It is possible to pull two cat6 down a common garden hose provided you use a draw wire, but three is impossible for more than a few metres. Or you can purchase cat6 externally-rated cable, which has an additional casing and a grease fill. It is horridly messy stuff to terminate though.

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Another option is to use fibre, but the prices generally rule this out.

Answer 7

RJ45 connector itself can impact the link. Be careful that there is some for single-stranded, multi-stranded copper pairs.

There is rj45 for cat5e cat6 cat7 ....

Answer 8

Don't use crimped ends. Period. Won't certify (yes, there are exceptions to every rule, depending on length, and actual RF/ Radiation interference) CAT6/ CAT6a. Use keystone jack's, and patch cables to your desired/ required bandwidth.