
How a bad RJ45 termination can ruin a cable - cyanoacry
http://www.bluejeanscable.com/articles/terrible-terminations.htm
======
beloch
"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!

~~~
GhotiFish
Wait. I didn't know this. They send inverse signals? Really? Does that mean
that long cat-5 cables made with the wrong standard wont work on some
equipment?!

~~~
cnvogel
You are mentioning two things. 1) yes, they send send signals, and their
"inverse" over a pair of cables. That's guaranteed by the use of transformers
on your network card/network switch. Current that the transformer sends in one
line of a pair, has to be returned in the other pair.

[https://www.google.de/search?q=ethernet+transformer&tbm=isch](https://www.google.de/search?q=ethernet+transformer&tbm=isch)

On an old 10MBit or 100MBit/s card (10BaseT, 100BaseT) on each device there
will be one pair to send data out, and one to receive data. This uses up 4
pins on your RJ45 connector, the other 2 are unused. The pair that is used on
your network card to send out data are pins 1 and 2. The pair that is used on
your network card to receive data is on pins 3 and 6.

The 2nd thing you mention are the two standards TIA/EIA-568 assigns colors to
pins, and they have a version A and B where the colours of pair 1/2 and pair
3/6 are swapped.

[https://en.wikipedia.org/wiki/TIA/EIA-568](https://en.wikipedia.org/wiki/TIA/EIA-568)

Hence, when you have a cable where one side is wired according to "A" and the
other is wired according to "B" you have something that, in the old days, was
called a cross-cable, which you could use to directly connecto two computers
with each other, without having a hub or switch in between. Which is very
useful, especially if you'd connect e.g. two switches in two buildings with
each other.

    
    
        Tx 568A               568B  Tx
     1  o---white----\   /---white---o
     2  o---green---- \ /----orange--o
                       X
     3  o---white---- / \----white---o
     6  o---orange---/   \---green---o
        Rx                          Rx
    

But because miswirings regarding the two color schemes were so frequent, and
connecting routers/switches/computers directly using "straight" cables was so
convenient, most devices manufactured after the 90s can swap these pairs
internally automatically. Hence no matter if you have a strait or cross-cable,
or a miswired 568A/B installation computers will just function fine.

With 1000BaseT (Gigabit-Ethernet) data is transmitted and received on all
pairs simultaneously, and also this miswiring is automatically detected and
taken into account.

------
PhantomGremlin
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)

------
skylan_q
_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
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.

------
chx
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
> "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
Wasn't that Nixon rather than Reagan?

~~~
icebraining
Yeap:
[http://en.wikipedia.org/wiki/Madman_theory](http://en.wikipedia.org/wiki/Madman_theory)

------
BryanB55
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
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
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
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.

------
ars
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.

------
bluedino
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.

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

------
tokenadult
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-n...](http://www.bluejeanscable.com/articles/good-better-best-or-not.htm)

------
GutenYe
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?

~~~
roel_v
Does anyone know of affordable cable testing equipment? I.e. not the ones with
8 leds that just test whether there's a connection, but one that actually
measures the performance? Fluke is way expensive, I imagine there must be
cheaper products that don't provide all the features and build quality of
Fluke but that will still give poor old me who only wires his own house and
home office some assurance that I didn't screw up completely?

~~~
cnvogel
A Gigabit Ethernet PHY has to do quite some signal processing (line
equalization) for its normal function. And there are a few chipsets that allow
you to inspect the link parameters in quite some detail. For example, have a
look here for screenshots of the broadcom advanced control suite.

[https://cs.uwaterloo.ca/~brecht/servers/docs/PowerEdge-2600/...](https://cs.uwaterloo.ca/~brecht/servers/docs/PowerEdge-2600/en/Broadcom/UG/trouble.htm)

The link has to run in 1000BaseT-Mode to make the tools show any meaningful
output, so have a known-good switch connected to the "other" side. I had used
them in a distant past (must have been 10 years ago or so) to find the "best"
links in an otherwise messed up building installation that could be reliabily
be used for higher transmission speeds.

It's of course much less information that what you'd get from a proper
ethernet cable analyzer, but much, much more than what a simple "yes, I can
ping the other side" can give you.

------
sumanthvepa
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!

------
Animats
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
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...?

~~~
PhantomGremlin
I hate downvotes. I usually upvote when I think someone has been unfairly
downvoted. I _very_ _rarely_ downvote, and yet I was one of your downvoters.

It's clear that you're "ignorant" of the black magic involved in high speed
communication. I felt that your post amounted to "I don't understand this
stuff ... therefore it is probably a scam".

As others have pointed out to you, at high enough speeds things become very
analog instead of digital. You can literally fit entire Ethernet packets into
a twisted pair cable. Packets can be short enough that they exist completely
"in the wire". That's a lot different than what a "premium audiophile cable"
does.

If you ever want to learn just how much "black magic" there is, read Howard
Johnson's books.[1] The information is somewhat dated, nowadays things are
even weirder.

[1]
[https://en.wikipedia.org/wiki/Howard_Johnson_%28electrical_e...](https://en.wikipedia.org/wiki/Howard_Johnson_%28electrical_engineer%29)

~~~
userbinator
_It 's clear that you're "ignorant" of the black magic involved in high speed
communication. I felt that your post amounted to "I don't understand this
stuff ... therefore it is probably a scam"._

"ignorant"? That's _really_ jumping to conclusions...

I've worked with DDR, DDR2, PCI, PCIe, and USB (2.0 only, but that's still
480MHz), in mass-produced designs. Also some proprietary busses operating in
the 600-800MHz range. It doesn't have to be perfect. That is what is so great
about digital signaling.

My post is more of a "I know from experience how much you can get away with,
and fancy test equipment that can tell the difference does not always reflect
how something performs in practice."

On the other hand, I won't comment on high-frequency _true analogue_ stuff
like microwave/RF.

~~~
PhantomGremlin
I see the point that you and 'parennoob' are making. The word "ignorant" was a
poor choice on my part.

