Ethernet point no internet

[Barnaby Stedman]

I’m no expert on this, but do like to understand things, and know it’s to do with using a ‘balanced signal’ for low-noise transmission.

On each pair, there is a +ve-going and -ve-going signal, with only the difference them being detected at the far end. If there’s external noise induced on the line, it will usually appear on both wires equally, so remains undetected, as any noise waveform simply provides a signal on both wires equally, not affecting the difference signal. Result: a magically clean signal in a noisy environment!

The twisting reduces cross-talk between pairs in a multi-pair cable. Consider if, due to the extreme proximity of all those little wires, one of a pair might receive a larger crosstalk signal that its partner, it will be unbalanced, affecting the difference signal and so be resolved at the other end as noise, messing up fast data comms.

But if the pairs are twisted, the crosstalk hits one strand first for a bit, then the other for a bit, and so on. Therefore the crosstalk signal is magically applied to each pair’s partner equally. It then ‘looks’ like external noise at the other end and is unresolved.

Twist frequency differs so that different pairs don’t keep crossing at the same points again and again, reducing the cancellation effect.

Clever ennit?

I think I've got that essentially right, but if there are any comms network designers on here who know better, please take over!

(cf. Balanced professional microphone cabling using 3-pin XLR connectors and shielded two-core interconnects).

As being a bit of a data and as it happens live sound guru myself I can only agree with you. What you are saying is dead correct.

 

[davesparks]

haven't done ethernet sockets before but hundreds of bt sockets which I hadn't had any problems with.
To my mind if the colours match at both ends which they do and I have tested to check they shouldn't stop anything working. But do you think the fact they are untwisted would affect the quality of connection ?

And I only meant neater in a sense that they weren't tight without any slack

BT sockets are completely different and a bit of untwisting doesn't usually affect them.
The colours need to be in the correct places so that each twisted pair has the correct data signal on it. Mixing the signals between different pairs will likely turn the data into nonsense.

The twisted pairs are used to cancel out interference, being twisted together ensures that both cores receive the same interference so that it can be cancelled out at the receiving end. The number of twists per metre is tightly controlled in the manufacture of the cable for this reason.

 

[davesparks]

haven't done ethernet sockets before but hundreds of bt sockets which I hadn't had any problems with.
To my mind if the colours match at both ends which they do and I have tested to check they shouldn't stop anything working. But do you think the fact they are untwisted would affect the quality of connection ?

And I only meant neater in a sense that they weren't tight without any slack

BT sockets are completely different and a bit of untwisting doesn't usually affect them.
The colours need to be in the correct places so that each twisted pair has the correct data signal on it. Mixing the signals between different pairs will likely turn the data into nonsense.

The twisted pairs are used to cancel out interference, being twisted together ensures that both cores receive the same interference so that it can be cancelled out at the receiving end. The number of twists per metre is tightly controlled in the manufacture of the cable for this reason.

 

[davesparks]

This is an excellent example why sparks should not do a network engineers job. (or aerials for that matter).

No it isn't, there are many electricians who have the knowledge and experience to do this correctly.
This is another example of why someone shouldn't just have a go at doing something without seeking the knowledge or training to do it correctly.

 

[rsgaz]

The cable jacket should stop as close to the module as possible.

The jacket should be cable tied to the strain relief loop, hence the tiny little cable tie usually included with the modules.

 

[robd]

No it isn't, there are many electricians who have the knowledge and experience to do this correctly.
This is another example of why someone shouldn't just have a go at doing something without seeking the knowledge or training to do it correctly.

I think the first statement was a bit strong but I'll take the 2nd one!

Basically a good customer said to me can you put me a point in for my internet so I don't have to use wireless. I was already taking the floor up and fishing cables for other jobs so I said it's not something I normally do but yes ok.

Anyway thanks to you all for your input it's now working I re-terminated, shorter and swapped the orange and white over to where it should be. Customer very happy and I didn't charge them for the sorting out. I am happy to stand here and be judged but overall I'd say thanks for your all your help, I do realise it's free advice from people but I've spent two unpaid hours on it and do try and help people on here where I can and where other people haven't already beaten me to it. The main thing is 1. I know something I didn't before and 2. Customer's got what they asked for and is happy.

Thanks again all

 

[robd]

Here's the 2nd socket after sorting

 

[Spoon]

Here's the 2nd socket after sorting

View attachment 49364

Where is the cable tie mate?
See @rsgaz post above.

 

[robd]

Where is the cable tie mate?
See @rsgaz post above.

Nowhere to hook it on there wasn't one in the pack either. It's not going anywhere.

 

[Squid]

Here's the 2nd socket after sorting

View attachment 49364

Its upside down and you need a manicure, tsk........

 

[Squid]

Ladies and Gentlemen remember the B wiring standard means British the A standard is for Arseholes errrr I mean the Americans......... ;o)))))

 

[Simon47]

There's (from memory) EIA 258A which splits all the pairs but makes sense for multi-line phones. Then there's EIA 258B which is the same layout as EIA 568A which makes sense for data connections.
The computer world stanardised on 258B for Ethernet a long time ago.

As already said, the twisted pairs are vital to carrying the signals properly - if you split the pairs then things just don't work. For 100M ethernet, there'll be two pairs carrying something like 125 MHz signals. For gigabit ethernet there's four pairs carrying something like 300MHz signals. Numbers could be off, but it's in the 100MHz up range.
By contrast, the standard phone line was only ever intended to carry up to 3 kHz. That changes with xDSL which uses up to a few MHz, but that is adaptive in terms of working with what the line will support.
So it's the difference between something that would almost work over damp string, and something that needs to work as a transmission line for what we'd once have considered to be radio (IIRC the old VHF TV was lower frequency !)

As already said, some sparkies know how to terminate network cables - but IME far more have no idea, and many of them have no desire to learn. Just like most of you would be "reluctant" to take on someone else's project to connect up and sign off - I've learned to be "wary" when taking on a network job where the sparkies have run all the cables and fitted the sockets and I "just" have to connect up the other end and test them.

 

[Charlie_]

B is crossover which is for network wiring..
A is straight through for device to device communication e.g: pc to pc

 

[Deleted member 26818]

The fact that the wiring colours have been terminated incorrectly should not be a factor if both sockets have been wired the same.

 

[robd]

The fact that the wiring colours have been terminated incorrectly should not be a factor if both sockets have been wired the same.

Would have been true if I hadn't crossed a pair I think. So long as the pairs are together and the same at both ends would have been ok. And I had untwisted the pairs.