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Author Topic: master socket wiring puzzle  (Read 2432 times)

jamesbob

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master socket wiring puzzle
« on: September 06, 2020, 09:07:43 PM »

Investigating a VDSL performance issue I ran the following DSL sync speed and speedtest.net tests in the following scenarios:

  • modem plugged into extension socket (house has no landlines plugged in or any other use of extension sockets
  • model plugged into master socket
  • model plugged into master socket with faceplate removed (the internal socket is not accessible with the faceplate on)

In short - the performance in the first 2 scenarios is similar, but drastically improved in scenario 3.

  • in the normal non-master socket the sync speeds are as previously reported - DSL stats of 28.8 Mbs down and 6.9 Mbs up
  • master socket normal socket  - DSL stats of 33.1 Mbs down and 6.0 Mbs up ... and speedtest.net benchmark of 30.58 Mbs down and 5.37 Mbs up
  • master socket faceplate removed, internet socket - DSL stats of 40Mbs down and 9.0 MBs up  ... and a speedtest.net benchmark of 38.18Mbs down and 8.17 Mbs up

The following observations are also interesting:

  • The SNR with the faceplate removed is 11 downstream. And with the faceplate on it is 7.
  • The Fritzbox 7530 also reports "line branching" which is 2 at the extension socket, 1 at the master socket, and 0 (actually not reported) with the faceplate removed.

This is puzzling because it suggests that having the faceplate attached causes significant degradation of the signal.

Is this correct?  What can I do about it?

The house is a new build, about 2.5 years old, and all the street wiring is new because the entire street is new. Does this mean the wiring in the house has been done badly?

What can I do to improve the signal to the extension socket. To be clear, there is no landline installed, and there is only 1 extension socket in a bedroom, and the only item plugged into the BT wires is a VDSL modem.

Screenshots attached if it helps diagnose the issue: (that sync speed of exactly 40000 seems suspicious...)

---

UPDATE  - I have since found that the house has a phone extension socket in every room! I didn't notice these before. They are not used. Only one socket is used for the VDSL model.


« Last Edit: September 07, 2020, 10:10:16 PM by jamesbob »
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mofa2020

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Re: master socket wiring puzzle
« Reply #1 on: September 06, 2020, 09:38:10 PM »

Maybe the extension wire is causing a problem at the master socket and makes it worse at the extension socket that could be the case as the extension (wiring or socket makes things worse), how is the extension wire connected to the master socket?
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jamesbob

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Re: master socket wiring puzzle
« Reply #2 on: September 06, 2020, 10:24:45 PM »

Good question - how is the extension wire connected to the master socket?

I'm not an expert so I don't know. Attached is a photo in case anyone more expert than myself can see.

Is this something I can fix? Or do I need to call an engineer?
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siofjofj

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Re: master socket wiring puzzle
« Reply #3 on: September 06, 2020, 10:37:47 PM »

The house is a new build, about 2.5 years old, and all the street wiring is new because the entire street is new. Does this mean the wiring in the house has been done badly?
I'm afraid new build houses are notorious for having very poor telephone extension cabling in them, usually as a result of it being put in by people who don't understand the complexities of RF transmission on twisted pair wiring (which is what xDSL is). Common issues are the use of inappropriate cable (i.e. not twisted pair, but standard alarm cable or similar) or the application of 'star-wiring' (i.e. multiple extensions radiating from a central point).

Good question - how is the extension wire connected to the master socket?
The extension wiring terminals are in the cam-lock connector in the bottom left of your photo and connect to the top (IIRC) row of pins in the test socket. With the faceplate off these are disconnected, and aren't touched by anything else you plug into the test socket since standard BT plugs only have contacts on one side.. The faceplate plug is doubled sided with both sides connected together, so when you plug it in the extension wiring also gets connected to the line.

The reason this harms the broadband, even with your router connected to the master socket, is that the extra wiring can pick up interference and inject it onto the phone line. Additionally, the RF xDSL signal travels up the extension wiring, gets reflected at the unterminated end (or multiple ends if you have star wiring) and then interferes with itself when it gets back to the master socket.

Is this something I can fix? Or do I need to call an engineer?
Yes, you absolutely can fix this (and in fact should not call out an Openreach engineer since problems caused by your own internal wiring attract large charges) subject to basic wiring skills.
The first question is, do you need the extension? If not, simply remove the wires from the cam-lock connector at the bottom left of the photo, replace the faceplate, then connect your router to the master socket and all will be well. If you need the extension, we may be able to explore other possibilities with you.
« Last Edit: September 06, 2020, 10:44:45 PM by siofjofj »
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burakkucat

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Re: master socket wiring puzzle
« Reply #4 on: September 06, 2020, 10:50:52 PM »

The house is a new build, about 2.5 years old, and all the street wiring is new because the entire street is new. Does this mean the wiring in the house has been done badly?

Unfortunately that is often the case. Either incorrect specification cable is used or it is incorrectly connected.

Quote
Screenshots attached if it helps diagnose the issue: (that sync speed of exactly 40000 seems suspicious...)

Ignore the "Max" and "Min DSLAM throughput" lines. Concentrate on the next two lines: "Attainable throughput" and "Current throughput". Look at the screenshot labelled "19:42 6th Sep internal master socket". (What you call the "internal master socket" is actually the test socket.) Your current throughput of 40000/9039 kbps DS/US coupled with the SNRmargin of 11 dB and 6 dB DS/US tells me a number of things:
  • You are provisioned with the Openreach 40/10 Mbps DS/US service.
  • You are achieving the 40 Mbps limit on the DS, hence the excess DS SNRmargin of 5 dB. (11 dB - 6 dB = 5 dB)
  • The wiring to the extension socket or the way it has been connected is defective. (By using the test socket the extension wiring is auto-disconnected.)
Openreach will happily attend and fix it. But you will be required to pay the charges for time and materials. You will looking at a price in excess of 100.
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mofa2020

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Re: master socket wiring puzzle
« Reply #5 on: September 06, 2020, 11:05:06 PM »

Ok, so this test socket has pins up and down (up connected to BT lead cable and down connected to the bottom left) by removing the faceplate you are actually disconnecting the extension wire from all the master socket completely (so it is dead end where it is connected and not live on BT wiring) so it is either the extension wiring or the connection inside the extension socket that is causing the problem all the way back to the master socket...
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burakkucat

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Re: master socket wiring puzzle
« Reply #6 on: September 06, 2020, 11:08:33 PM »

so it is either the extension wiring or the connection inside the extension socket that is causing the problem all the way back to the master socket...

Yes, exactly.
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mofa2020

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Re: master socket wiring puzzle
« Reply #7 on: September 06, 2020, 11:10:16 PM »

Just for info, this place is new to you so this setup as it is was not working correctly ever since you moved in?! from what I see in the master socket picture there are 3 wires connected inside the extension connector so could it be just as simple as the ring wire that from what I know can cause issues if connected?
« Last Edit: September 06, 2020, 11:16:22 PM by mofa2020 »
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jamesbob

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Re: master socket wiring puzzle
« Reply #8 on: September 06, 2020, 11:37:06 PM »

Thanks everyone for the suggestions and advice - being a newbie I am learning a lot!

So I now understand that taking off the faceplate disconnects the extension cabling - which can be a cause of interference / reflection.

Sadly I can't connect the modem directly to test socket, I need to have the modem in the bedroom.

The challenge I think is therefore to reduce or remove the interference. Are there simple tests I can do to identify the cause - and what can I do about them?

I suspect changing the actual wiring might be a big project which I can't do myself.

@mofa2020 - what is a "ring wire"? Should I cut it? Do I need it for the extension wiring to the bedroom?

Would a closer photo tomorrow help anyone identify the wiring in the master socket?

Would replacing the master socket and extension socket's with better quality sockets help?


-- update

currently reading this to see if it offers any helpful remedies: https://kitz.co.uk/adsl/socket.htm
« Last Edit: September 06, 2020, 11:47:11 PM by jamesbob »
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jamesbob

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Re: master socket wiring puzzle
« Reply #9 on: September 06, 2020, 11:46:31 PM »

should I cut this orange "ring" wire ?

(see pic attached)
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mofa2020

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Re: master socket wiring puzzle
« Reply #10 on: September 06, 2020, 11:54:01 PM »

@mofa2020 - what is a "ring wire"? Should I cut it? Do I need it for the extension wiring to the bedroom?

If one of the 3 extension wires is actually a ring wire (but I am not sure it is so wait for an expert Kitzen to confirm it, or maybe I am wrong) but if it is, you do not need it at all for the modem to work in the bed room, it is just an unused wire that can pick interference (acts like antenna) and affect the DSL signal.
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burakkucat

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Re: master socket wiring puzzle
« Reply #11 on: September 06, 2020, 11:55:29 PM »

If you are competent with a screwdriver and a camera then you will be able to help us help you.

Please try to perform the following steps:
  • Disconnect the plug, currently in the test socket.
  • With good lighting illuminating the master socket, take a photograph of it -- square-on.
  • Remove the two screws that hold the master socket in the backing box and gently remove the socket. Allow it to hang from the wires such that the cables (hopefully two) and the wires from the cables can be clearly seen. It is important that a clear view of the colours of the wires is obtained. Take a photograph.
  • Now go to the extension socket. Remove the two screws that hold it in the backing box and gently remove the socket. Again, just as above, allow it to hang from the wires and take a clear photograph of what can be seen.
  • Post copies of the three photographs (in the original, native, resolution) to a photo-sharing site and then post the link to the images here.
Hopefully we may see sufficient detail to then be able to guide you with remedial action.

should I cut this orange "ring" wire ?

(see pic attached)

No. Please don't rush at things. Let us see the full situation, first.
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burakkucat

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Re: master socket wiring puzzle
« Reply #12 on: September 07, 2020, 12:01:57 AM »

Another thought has just come to me . . . You have not yet shown us the face-plate that you have removed from the front of the NTE5C, the master socket. So please also photograph that.
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jamesbob

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Re: master socket wiring puzzle
« Reply #13 on: September 07, 2020, 12:49:28 AM »

Thanks @burakkucat - I'll do that tomorrow.
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siofjofj

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Re: master socket wiring puzzle
« Reply #14 on: September 07, 2020, 09:35:06 AM »

    Just a couple of additional thoughts now I have a fresh head this morning.
The Fritzbox 7530 also reports "line branching" which is 2 at the extension socket, 1 at the master socket, and 0 (actually not reported) with the faceplate removed.[/li][/list]
I didn't notice this last night, but it looks like your modem has the capability to detect reflections of the DSL signal from unterminated extensions (so called bridge-taps). I have never seen this feature before, though it is certainly possible to do this by analysing the how the attenuation of the DSL signal varies with frequency. If your wiring simply went between your master socket and your extension, with no intermediate joints, there would be no bridge taps when connected to the extension, and one bridge tap when connected to the master socket with the faceplate fitted. Given that your modem is detecting two at the extension socket and one at the master (are you sure it was this way round? I'd expect the opposite) however, it looks like the wiring is more complex than that. Are you absolutely certain there is only one extension socket?

With regard to the bell wire, the purpose of this is to supply an AC coupled ringing signal to make the mechanical bells ring on old phones. As it is an unbalanced wire (i.e. not part of a twisted pair) it can collect interference which gets injected onto the line. However, modern master sockets (which yours is) connect the ring wire via an inductor in order to block high frequency junk, so this shouldn't matter in this case. As burakkucat says, leave it for now until we can see the full picture.
« Last Edit: September 07, 2020, 09:37:47 AM by siofjofj »
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