9 ms·

How a bad RJ45 termination can ruin a cable

113 points by cyanoacry 12y ago

sumanthvepa 12y ago
Absolutely fascinating. I've been crimping my own RJ45s for a while now, surprised that I'm not quite getting the speed I'd hoped for with CAT6. Lesson learned. Thanks!
BryanB55 12y ago
I just terminated a ton of CAT5e for security cameras and I can definitely see the margin of error begin high. It sucks to do, I feel like there should be an easier way to terminate them that doesn't involve carefully trying to align the right color combination and holding them steady enough to then align them in that same order with tiny slots on the plug.
- rdl 12y ago
  Yes, the correct solution is structured cabling with punchdown jacks, punchdown patch panels, and commercially manufactured and certified patch and lobe cords. No one is going to pay commercial electrician rates, even lv, to futz around with a crimper, especially when one little plastic tab getting snapped off means a cable needs to be re terminated.
  - mturmon 12y ago
    I have done a lot of punchdown jack connections, and a few crimp connections, and I have to agree that the punchdown connections (into a female jack which receives a patch cord, and the patch cord goes to the device) have been much more deterministic. It is rare when one does not work the first time. I wasn't using structured cabling, just ordinary Cat5e cable. But I think for a security camera, as in the parent comment, which may be getting PoE, the tidiest connection would use a crimp-down male RJ45. I would not enjoy being up on a ladder fussing with a crimping tool and 8 stubby wires.
    - DrPhish 12y ago
      Still better to put a jack (facing down!) into a surface mount box and patch into the camera. When you are working with outdoor gear, put the surface mount box into a waterproof jbox. Even if you are going into gear with a gasket that requires you to crimp an end on a patch cable, it's still better to do it this way. Jack-to-jack lasts so much longer and is so much more reliable, I will almost never allow crimped ends anywhere in my networks. Patch cables are a commodity, horizontal runs are an investment.
skylan_q 12y ago
But it's a mistake to assume that just because network signals are electrical, any electrician is automatically qualified to put a network together. This can't be stressed enough, especially when running horizontal cabling through buildings. We've had issues in taking ownership of network infrastructure that was installed by "reliable" electricians. Some advice: Make sure that you keep a decent bend radius on the connections and that you're able to sustain (near) peak transfer over the connection. Cable testers and certifiers add to the confidence that you've got a solid connection. Modern switches will also report on CRC errors and issues that come from physical layer problems.
- beloch 12y ago
  I once worked in an optics lab that had been really well planned. Each bench had network connections and optical fiber connections that go to each bench in each room of the lab. The idea was that you could build something in one room and send it's output to another room just by using the right fiber port on your bench. No need to string fiber optics along the floor and through doors! Planning was undone by execution unfortunately. The installers claimed they had worked with fiber optics before and could do a great job. They installed the cat5 cables with such tight turns that only half of them work. The fiber optic cables had the same tight turns, and fiber is more sensitive to bends. The loss between benches just 4 meters apart is in excess of 30 dB! Totally unusable for practically all experiments.
- mturmon 12y ago
  Having diagnostics on the switch can be a big plus. I wired a long run, partly underground, myself, and it was erratic. I had two parallel cat5e lines, and I could only use one. After I got the better switch, it was able to tell me approximately how far along the cable the fault was, which was enough to narrow down the problem. I checked bend radius and re-terminated, and problem solved. So nice to work with good equipment. It turns voodoo into engineering.
GutenYe 12y ago
I've crimped some RJ45s for my own house, but always got wrong, and have to crimp 3 or more times to make it work (cut off connectors at both side, and re-crimp again). Any tips on it?
- _kerbal_ 12y ago
  Correctly crimping RJ45 is one of those things that seems impossible, but once you get the hang of it works out most of the time. - Make sure your wires are extending far enough into the plug, you should see the wire fully overlap the brass spades. - Confirm you have the right wire layout by looking through the plug before you crimp the cable. - As mentioned in the article, the tail part of the connector is meant to cover the tip of the cable's insulation to provide a bit of stress relief, make sure it's not too short.
- raldi 12y ago
  I never had any trouble; maybe you're using poor-quality cabling, or a lousy crimper. Do you happen to have one of these bad cables lying around? A close-up photo of the end might reveal something.
- rdl 12y ago
  Make sure you are using solid wire cable with solid wire connectors, or stranded wire cable with stranded wire connectors. They are quite different. I used to make a lot of Ethernet cables, but pretty much stopped when I went to Cat 6. Beyond that, you need to be careful to remain consistent 568B or 568A, etc., and it gets messy. Almost all 10GE I've ever used has been fiber, though. Almost had a physical altercation with someone who wired a building straight through vs correctly. Amazingly you could still get a 10M link on longer runs, or a 100M link on patches.
  - Dylan16807 12y ago
    Wait, what did the person you argued with do wrong? I don't understand.
    - function_seven 12y ago
ars 12y ago
Even home electrical circuits can have crosstalk. People sometimes find that LEDs and even florescent lights glow dimly even with the switch off. The is caused by magnetic induction in lines, which is in turn caused by not running the hot and neutral near each other.
beloch 12y ago
"Most of us, if we do not deal in high-speed digital signalling, have a kind of "DC Circuits" understanding of wiring where the most important thing is simply that the wires connect the right points together." An example of this is thinking that the order of wires in your crimps doesn't matter so long as it is consistent at both ends. This is emphatically not the case! Each twisted pair in a cat5 cable is intended to carry a signal and it's inverse. If you add a signal to it's inverse you should get nothing, but if noise has skewed both signal and inverse, the result of addition will be the isolated interference you need to subtract from your signal. Cat5 connections rely on this noise cancellation to work, as the wires used have little or no shielding. If you put wires into the wrong order so that signals are not paired with their inverses, this noise cancellation system is totally fubar'd and will likely make things worse than if there was no noise cancellation at all. It might work over a few meters, but longer cables are almost guaranteed to fail. Pick a wiring standard (568-A or 568-B) and stick to it. If you do this, it's pretty hard to mess up anything else so badly that your cables won't work. Bluejeanscables is a cable manufacturer, so they're probably exaggerating how hard it is to make a good cable. In particular, their "buy american" schtick is not very applicable to cabling. Monoprice is functionally equivalent, even if it's from China. Note: If you're wiring your home, be sure to use plenum grade cable. Other cables may be flammable and fire codes tend to disapprove of having flammable cords running through your home. Also Note: I am not an electrician. I just found out the hard way by making bad cables for my home. If you buy one $50 spool of cable, $5 of terminations, and a $20 crimp tool you'll never have to pay for network cables again. I'm not sure if it would be worth it now, but it certainly was 10 years ago!
- rdtsc 12y ago
  I had no idea there were even 2 wiring standards. Only found out last year when trying to connect via an older cat5 cable that was going from my garage to the office at my house. And after reading your comment also realized it is probablhy not up to code as well...
  - Intermernet 12y ago
    You actually require both wiring standards to create a cross-over cable. The tricky bit I've found (and I also used a Fluke tester on all cables I manually terminated) is that when terminating cat-6 cables, the inner two pairs had to be separated and terminated perfectly symmetrically. With cat-5, or 5e, you seem to be able to get away with some sloppiness, but with cat-6 you need to think like a seamstress. Those wires need to be exactly in place, and exactly the right length. I used to find cable termination quite a zen-like experience. I'd do a hundred cable terminations, then fifty cable tests, and very rarely get to smile at a perfect result.
imperialdrive 12y ago
doesn't show the after picture - if you're the author, please show... it kind of ruins the point of the article otherwise
Animats 12y ago
The test equipment required for cable testing is expensive. Entry level from Fluke is CableIQ at $1200. Fluke cable testers go up to about $45K.
userbinator 12y ago
I don't find this article particularly convincing; in fact it feels suspiciously to me like the same sort of technical arguments made by some "premium audiophile cable" vendors. The fact that your fancy test equipment can detect significant differences between your cables and others' is not necessarily correlated with how well they actually work in practice. This doesn't look like one of those truly insane companies who sell $1500/m cables to a niche audience, but they're using some of the same techniques... The fact that differences can be seen in the analogue domain is also not a direct correspondence to how the cable will perform digitally. Ethernet is digital, and as long as the signals pass the thresholds at the receiver, there will be no difference. The most unusual thing here is that they didn't mention at all whether they actually solved any of the problems the customer originally had, which would be the true validator of their theory. (If they did, wouldn't it be a great thing to mention?) "Network performance issues" are vague - I was expecting to see tests of throughput/packet loss between the original and reterminated cables. Edit: downvotes. Care to explain...?
- mjrpes 12y ago
  It is similar to DSL connection issues cause by spotty telephone wiring. Cross talk and outside interference raise noises levels on the line and the devices on either end can't tell the signal from the background noise. This is different from audiophile cabling, which is usually over short distances where noise is not an issue.
- wl 12y ago
  You'd be surprised at just how analog high speed digital is. The data represented by the signal is digital, but the signal over the wire is an analog waveform more complicated than simple high and low voltages. Poor cables can absolutely cause high BER and lower performance. If you've ever watched digital television over the air and seen the picture drop out, it's a similar thing. A lot of the audiophile nonsense is only nonsense in its application to the ridiculously low frequency world of audio. But when we're dealing with transmission lines, yes, cables absolutely do matter.
  - userbinator 12y ago
deleted 12y ago
[deleted]
chx 12y ago
Hey, Blue Jeans Cable! These are the guys who told Monster Cable to get stuffed. Very nice way of dealing with a patent troll: http://www.bluejeanscable.com/legal/mcp/response041408.pdf http://www.bluejeanscable.com/legal/mcp/response041408.pdf transcribed at http://www.audioholics.com/news/blue-jeans-strikes-back http://www.audioholics.com/news/blue-jeans-strikes-back Best part: "Not only am I unintimidated by litigation; I sometimes rather miss it."
- cbd1984 12y ago
  > "Not only am I unintimidated by litigation; I sometimes rather miss it." Rather Reaganesque: If they think you're crazier than they are, they'll leave you alone. (Note: Doesn't work if you have no way to hurt them and they know it, or if they're convinced you have no way to hurt them.)
  - arethuza 12y ago
    Wasn't that Nixon rather than Reagan?
    - icebraining 12y ago
      Yeap: http://en.wikipedia.org/wiki/Madman_theory http://en.wikipedia.org/wiki/Madman_theory
PhantomGremlin 12y ago
Off topic, but I can't resist re-posting the following. It will bring tears of joy to anyone who hates patent trolls. Blue Jeans Cable was mentioned on HN a few months ago in the context of Monster Cable sending them a letter threatening to sue them for patent and trademark infringement. An HN poster characterized their response letter to Monster Cable as: "That. letter. is. glorious." Here are just a few snippets: if you file on this sort of basis, you are in Rule 11 frivolous-claim territory ... You are required, as a matter of legal ethics, to display good faith and professional candor in your dealings with adverse parties, and you have fallen miserably short of your ethical responsibilities ... Read the patents narrowly, and Monster loses; read them broadly, and Monster loses. ... I spent nineteen years in litigation practice ... I am "uncompromising" in the most literal sense of the word. If Monster Cable proceeds with litigation against me I will pursue the same merits-driven approach: I do not compromise with bullies and I would rather spend fifty thousand dollars on defense than give you a dollar of unmerited settlement funds. ... Not only am I unintimidated by litigation; I sometimes rather miss it. http://www.bluejeanscable.com/legal/mcp/ http://www.bluejeanscable.com/legal/mcp/ https://news.ycombinator.com/item?id=8848842 https://news.ycombinator.com/item?id=8848842
tokenadult 12y ago
Another article on the same site (Blue Jeans Cable) makes the interesting point that some kinds of cable are more expensive not because they are better at reducing signal loss but because they are rated for more fire-resistance for certain kinds of installations.[1] The article points out that more expensive is not always better if by "better" you mean "less likely to distort the signal." [1] "Good, Better, Best -- Or Not?" http://www.bluejeanscable.com/articles/good-better-best-or-not.htm http://www.bluejeanscable.com/articles/good-better-best-or-n...
bluedino 12y ago
Another tip: Don't try to mix cat5 and 6 wire and connectors. The cat6 wire is larger, won't fit in the connectors for cat5, and the pins won't puncture the thicker insulation.

113 points by cyanoacry 12y ago

Absolutely fascinating. I've been crimping my own RJ45s for a while now, surprised that I'm not quite getting the speed I'd hoped for with CAT6. Lesson learned. Thanks!

BryanB55 12y ago

I just terminated a ton of CAT5e for security cameras and I can definitely see the margin of error begin high. It sucks to do, I feel like there should be an easier way to terminate them that doesn't involve carefully trying to align the right color combination and holding them steady enough to then align them in that same order with tiny slots on the plug.

rdl 12y ago
Yes, the correct solution is structured cabling with punchdown jacks, punchdown patch panels, and commercially manufactured and certified patch and lobe cords. No one is going to pay commercial electrician rates, even lv, to futz around with a crimper, especially when one little plastic tab getting snapped off means a cable needs to be re terminated.
- mturmon 12y ago
  I have done a lot of punchdown jack connections, and a few crimp connections, and I have to agree that the punchdown connections (into a female jack which receives a patch cord, and the patch cord goes to the device) have been much more deterministic. It is rare when one does not work the first time. I wasn't using structured cabling, just ordinary Cat5e cable. But I think for a security camera, as in the parent comment, which may be getting PoE, the tidiest connection would use a crimp-down male RJ45. I would not enjoy being up on a ladder fussing with a crimping tool and 8 stubby wires.
  - DrPhish 12y ago
    Still better to put a jack (facing down!) into a surface mount box and patch into the camera. When you are working with outdoor gear, put the surface mount box into a waterproof jbox. Even if you are going into gear with a gasket that requires you to crimp an end on a patch cable, it's still better to do it this way. Jack-to-jack lasts so much longer and is so much more reliable, I will almost never allow crimped ends anywhere in my networks. Patch cables are a commodity, horizontal runs are an investment.

skylan_q 12y ago

But it's a mistake to assume that just because network signals are electrical, any electrician is automatically qualified to put a network together. This can't be stressed enough, especially when running horizontal cabling through buildings. We've had issues in taking ownership of network infrastructure that was installed by "reliable" electricians. Some advice: Make sure that you keep a decent bend radius on the connections and that you're able to sustain (near) peak transfer over the connection. Cable testers and certifiers add to the confidence that you've got a solid connection. Modern switches will also report on CRC errors and issues that come from physical layer problems.

beloch 12y ago
I once worked in an optics lab that had been really well planned. Each bench had network connections and optical fiber connections that go to each bench in each room of the lab. The idea was that you could build something in one room and send it's output to another room just by using the right fiber port on your bench. No need to string fiber optics along the floor and through doors! Planning was undone by execution unfortunately. The installers claimed they had worked with fiber optics before and could do a great job. They installed the cat5 cables with such tight turns that only half of them work. The fiber optic cables had the same tight turns, and fiber is more sensitive to bends. The loss between benches just 4 meters apart is in excess of 30 dB! Totally unusable for practically all experiments.
mturmon 12y ago
Having diagnostics on the switch can be a big plus. I wired a long run, partly underground, myself, and it was erratic. I had two parallel cat5e lines, and I could only use one. After I got the better switch, it was able to tell me approximately how far along the cable the fault was, which was enough to narrow down the problem. I checked bend radius and re-terminated, and problem solved. So nice to work with good equipment. It turns voodoo into engineering.

GutenYe 12y ago

I've crimped some RJ45s for my own house, but always got wrong, and have to crimp 3 or more times to make it work (cut off connectors at both side, and re-crimp again). Any tips on it?

_kerbal_ 12y ago
Correctly crimping RJ45 is one of those things that seems impossible, but once you get the hang of it works out most of the time. - Make sure your wires are extending far enough into the plug, you should see the wire fully overlap the brass spades. - Confirm you have the right wire layout by looking through the plug before you crimp the cable. - As mentioned in the article, the tail part of the connector is meant to cover the tip of the cable's insulation to provide a bit of stress relief, make sure it's not too short.
raldi 12y ago
I never had any trouble; maybe you're using poor-quality cabling, or a lousy crimper. Do you happen to have one of these bad cables lying around? A close-up photo of the end might reveal something.
rdl 12y ago
Make sure you are using solid wire cable with solid wire connectors, or stranded wire cable with stranded wire connectors. They are quite different. I used to make a lot of Ethernet cables, but pretty much stopped when I went to Cat 6. Beyond that, you need to be careful to remain consistent 568B or 568A, etc., and it gets messy. Almost all 10GE I've ever used has been fiber, though. Almost had a physical altercation with someone who wired a building straight through vs correctly. Amazingly you could still get a 10M link on longer runs, or a 100M link on patches.
- Dylan16807 12y ago
  Wait, what did the person you argued with do wrong? I don't understand.
  - function_seven 12y ago

ars 12y ago

Even home electrical circuits can have crosstalk. People sometimes find that LEDs and even florescent lights glow dimly even with the switch off. The is caused by magnetic induction in lines, which is in turn caused by not running the hot and neutral near each other.

beloch 12y ago

"Most of us, if we do not deal in high-speed digital signalling, have a kind of "DC Circuits" understanding of wiring where the most important thing is simply that the wires connect the right points together." An example of this is thinking that the order of wires in your crimps doesn't matter so long as it is consistent at both ends. This is emphatically not the case! Each twisted pair in a cat5 cable is intended to carry a signal and it's inverse. If you add a signal to it's inverse you should get nothing, but if noise has skewed both signal and inverse, the result of addition will be the isolated interference you need to subtract from your signal. Cat5 connections rely on this noise cancellation to work, as the wires used have little or no shielding. If you put wires into the wrong order so that signals are not paired with their inverses, this noise cancellation system is totally fubar'd and will likely make things worse than if there was no noise cancellation at all. It might work over a few meters, but longer cables are almost guaranteed to fail. Pick a wiring standard (568-A or 568-B) and stick to it. If you do this, it's pretty hard to mess up anything else so badly that your cables won't work. Bluejeanscables is a cable manufacturer, so they're probably exaggerating how hard it is to make a good cable. In particular, their "buy american" schtick is not very applicable to cabling. Monoprice is functionally equivalent, even if it's from China. Note: If you're wiring your home, be sure to use plenum grade cable. Other cables may be flammable and fire codes tend to disapprove of having flammable cords running through your home. Also Note: I am not an electrician. I just found out the hard way by making bad cables for my home. If you buy one $50 spool of cable, $5 of terminations, and a $20 crimp tool you'll never have to pay for network cables again. I'm not sure if it would be worth it now, but it certainly was 10 years ago!

rdtsc 12y ago
I had no idea there were even 2 wiring standards. Only found out last year when trying to connect via an older cat5 cable that was going from my garage to the office at my house. And after reading your comment also realized it is probablhy not up to code as well...
- Intermernet 12y ago
  You actually require both wiring standards to create a cross-over cable. The tricky bit I've found (and I also used a Fluke tester on all cables I manually terminated) is that when terminating cat-6 cables, the inner two pairs had to be separated and terminated perfectly symmetrically. With cat-5, or 5e, you seem to be able to get away with some sloppiness, but with cat-6 you need to think like a seamstress. Those wires need to be exactly in place, and exactly the right length. I used to find cable termination quite a zen-like experience. I'd do a hundred cable terminations, then fifty cable tests, and very rarely get to smile at a perfect result.

imperialdrive 12y ago

doesn't show the after picture - if you're the author, please show... it kind of ruins the point of the article otherwise

Animats 12y ago

The test equipment required for cable testing is expensive. Entry level from Fluke is CableIQ at $1200. Fluke cable testers go up to about $45K.

userbinator 12y ago

I don't find this article particularly convincing; in fact it feels suspiciously to me like the same sort of technical arguments made by some "premium audiophile cable" vendors. The fact that your fancy test equipment can detect significant differences between your cables and others' is not necessarily correlated with how well they actually work in practice. This doesn't look like one of those truly insane companies who sell $1500/m cables to a niche audience, but they're using some of the same techniques... The fact that differences can be seen in the analogue domain is also not a direct correspondence to how the cable will perform digitally. Ethernet is digital, and as long as the signals pass the thresholds at the receiver, there will be no difference. The most unusual thing here is that they didn't mention at all whether they actually solved any of the problems the customer originally had, which would be the true validator of their theory. (If they did, wouldn't it be a great thing to mention?) "Network performance issues" are vague - I was expecting to see tests of throughput/packet loss between the original and reterminated cables. Edit: downvotes. Care to explain...?

mjrpes 12y ago
It is similar to DSL connection issues cause by spotty telephone wiring. Cross talk and outside interference raise noises levels on the line and the devices on either end can't tell the signal from the background noise. This is different from audiophile cabling, which is usually over short distances where noise is not an issue.
wl 12y ago
You'd be surprised at just how analog high speed digital is. The data represented by the signal is digital, but the signal over the wire is an analog waveform more complicated than simple high and low voltages. Poor cables can absolutely cause high BER and lower performance. If you've ever watched digital television over the air and seen the picture drop out, it's a similar thing. A lot of the audiophile nonsense is only nonsense in its application to the ridiculously low frequency world of audio. But when we're dealing with transmission lines, yes, cables absolutely do matter.
- userbinator 12y ago

deleted 12y ago

[deleted]

chx 12y ago

Hey, Blue Jeans Cable! These are the guys who told Monster Cable to get stuffed. Very nice way of dealing with a patent troll: http://www.bluejeanscable.com/legal/mcp/response041408.pdf http://www.bluejeanscable.com/legal/mcp/response041408.pdf transcribed at http://www.audioholics.com/news/blue-jeans-strikes-back http://www.audioholics.com/news/blue-jeans-strikes-back Best part: "Not only am I unintimidated by litigation; I sometimes rather miss it."

cbd1984 12y ago
> "Not only am I unintimidated by litigation; I sometimes rather miss it." Rather Reaganesque: If they think you're crazier than they are, they'll leave you alone. (Note: Doesn't work if you have no way to hurt them and they know it, or if they're convinced you have no way to hurt them.)
- arethuza 12y ago
  Wasn't that Nixon rather than Reagan?
  - icebraining 12y ago
    Yeap: http://en.wikipedia.org/wiki/Madman_theory http://en.wikipedia.org/wiki/Madman_theory

PhantomGremlin 12y ago

Off topic, but I can't resist re-posting the following. It will bring tears of joy to anyone who hates patent trolls. Blue Jeans Cable was mentioned on HN a few months ago in the context of Monster Cable sending them a letter threatening to sue them for patent and trademark infringement. An HN poster characterized their response letter to Monster Cable as: "That. letter. is. glorious." Here are just a few snippets: if you file on this sort of basis, you are in Rule 11 frivolous-claim territory ... You are required, as a matter of legal ethics, to display good faith and professional candor in your dealings with adverse parties, and you have fallen miserably short of your ethical responsibilities ... Read the patents narrowly, and Monster loses; read them broadly, and Monster loses. ... I spent nineteen years in litigation practice ... I am "uncompromising" in the most literal sense of the word. If Monster Cable proceeds with litigation against me I will pursue the same merits-driven approach: I do not compromise with bullies and I would rather spend fifty thousand dollars on defense than give you a dollar of unmerited settlement funds. ... Not only am I unintimidated by litigation; I sometimes rather miss it. http://www.bluejeanscable.com/legal/mcp/ http://www.bluejeanscable.com/legal/mcp/ https://news.ycombinator.com/item?id=8848842 https://news.ycombinator.com/item?id=8848842

tokenadult 12y ago

Another article on the same site (Blue Jeans Cable) makes the interesting point that some kinds of cable are more expensive not because they are better at reducing signal loss but because they are rated for more fire-resistance for certain kinds of installations.[1] The article points out that more expensive is not always better if by "better" you mean "less likely to distort the signal." [1] "Good, Better, Best -- Or Not?" http://www.bluejeanscable.com/articles/good-better-best-or-not.htm http://www.bluejeanscable.com/articles/good-better-best-or-n...

bluedino 12y ago

Another tip: Don't try to mix cat5 and 6 wire and connectors. The cat6 wire is larger, won't fit in the connectors for cat5, and the pins won't puncture the thicker insulation.