Slow speeds and bridge tap

Hi all. I've had my mum on the phone complaining of slow internet. In the absence of being able to go over and check it out for myself at the moment, I put her phone number into the BT DSL checker and a couple of things looked odd. Here's a screenshot: https://i.imgur.com/3Y0Hfbi.png

Firstly the max observed speed is a lot lower than expected, even below the handback threshold. Secondly I noticed that the bridge tap status is Yes. I've never known this before, only ever No or Unknown. Can someone fill me in on what this might mean? I've done a bit of googling, and from what I can gather it involves a single line serving multiple houses, and signals being reflected back causing errors, but to the best of my knowledge there's nothing like that. Unless there's part of an old setup still connected somewhere? It's an old house so the line has been in for several decades.

I've told her to report to BT, but just interested in what we're dealing with here.

Cheers all.

What you have seen is teh origins of a "bridge tap" these days it can mean having an extension run off teh line well before the filter/splitter and modem.

The signal travels down the tapping (spur) and is reflected back. At some frequencies it is in phase, at others, out of phase by 180 degrees and everywhere in between. Te length of te tap defines the frequency response so every one is different. When in phase the signal has little degradartion, increasing and increasing until 180 degrees or inversion is reached and at that point teh signal is totally negated resulting in several tones being unusable. If you look at a bits/tone graph, a brdge tap will show up as a notch and there will also be harmonic repitition of it.

So, EXACTLY what is teh layout of teh house ... how many sockets, and hwo are they all connected?

A bridge tap is often where extensions, or rather the cabling to extensions, are wired incorrectly and can considerably reduce observed connection speeds. A bridge tap can be as simple as the incoming line being split and terminating in more than one socket rather than at a single master socket with any extensions then wired to the master. Internal wiring is the customer's responsibility and is a chargeable repair however being on the customer side repairs can be carried out by others than BT.

When a bridge tap shows it doesn't automatically mean it's inside a property, we have had a bridge tap show several times, and each time it has nothing to do with the internal wiring as we only have a master socket with no other internal wiring.

The incoming line just goes to the master socket with no extensions running off it. It's a single socket NTE5 with a plug in microfilter which has the router and a single landline phoneconnected.

Then that should be an ideal set up ... and wouldn’t normally give the ‘bridge tap’ test result.

There, as another poster points out, times when ‘bridge tap’ shows as a test result, when in fact one doesn’t exist ........ but this is very rare indeed.

Openreach are not currently working within customer premises during the Covid-19 pandemic (except in exceptional circumstances) So raising a fault will get the line checked out to the nearest readily accessible point to the property.

Edited by Zarjaz (Sun 05-Apr-20 13:30:31)

Edited by deleted (Sun 05-Apr-20 13:36:38)

Edited - ta

OK, after speaking to the folks over the phone today, it turns out I'm wrong about the setup, and I think I've found the answer to the issue.

There is indeed another phone socket in the house, in a spare bedroom upstairs. This has clearly been wired up incorrectly however. The dropwire goes into the junction box under the eaves, and from there it actually splits two ways - one cable to the socket in the hallway, and then another cable (again directly from the junction box) to the upstairs socket! (Not used and installed before they moved in). They don't have anything connected to it, but clearly this is the bridge tap and presumably the cause of the slow speed.

Where do I stand on sorting this out? I suppose cutting the wires at the junction box, though not technically touching the OR network, but just disconnecting the unauthorized spur, would not be allowed as it's before the official master socket. I suppose if we got them out to sort it, it would be chargable?

In reply to a post by Zarjaz:

Then that should be an ideal set up ... and wouldn’t normally give the ‘bridge tap’ test result.

There, as another poster points out, times when ‘bridge tap’ shows as a test result, when in fact one doesn’t exist ........ but this is very rare indeed.

Openreach are not currently working within customer premises during the Covid-19 pandemic (except in exceptional circumstances) So raising a fault will get the line checked out to the nearest readily accessible point to the property.

I’ll take your word for it. I never once saw that myself.

I was incredibly confident in that “bridge tap” test result whenever I saw it even if I couldn’t find the actual culprit sometimes, maybe it was buried behind a wall or that sort of thing. If I couldn’t locate it I’d run a new lead-in entirely straight into the master socket and that would then return a normal test result.

The only time I can think that there would be a bridge tap in the network would be if they’re doing a cabinet changeover, and then that’s something done on purpose just while they’re wiring up the replacement cabinet and is temporary. Very rare though also.

In reply to a post by derby13:

Where do I stand on sorting this out? I suppose cutting the wires at the junction box, though not technically touching the OR network, but just disconnecting the unauthorized spur, would not be allowed as it's before the official master socket. I suppose if we got them out to sort it, it would be chargable?

That’ll definitely be what’s causing the reduced speed. You could cut the spur off at the junction box (BT18 or Above Ground Closure) certainly and that would sort it. Only concern there would be if you just cut it you’re leaving a stub of wire there that could corrode and cause problems, so I suppose it depends how well you think the junction box is doing keeping moisture out.

Edited by deleted (Sun 05-Apr-20 19:16:29)

>>The only time I can think that there would be a bridge tap in the network ...

As with many things there will be regional differences.

In my manor there are quite a few exchanges that have some teed up local main cables. One bar pair feeding 2 different cabinets. In some cases cabinets being a couple of km apart!

There are also frames that were condensed / moved and the old frames left teed in in the cable chamber or manholes close by. I had a contract to recover the tees on one of the largest exchanges in the UK a year or two back.

I’ll take your word for it. I never once saw that myself.

I was incredibly confident in that “bridge tap” test result whenever I saw it even if I couldn’t find the actual culprit sometimes, maybe it was buried behind a wall or that sort of thing. If I couldn’t locate it I’d run a new lead-in entirely straight into the master socket and that would then return a normal test result.

I used to be like you ... had heard a couple of colleagues claim they’d had it, but I was very dubious myself.

.. but, about three weeks ago, had exactly this . You could fit an NTE on the UG pair in the 66, put your tester in sync, and get the ‘bridge tap’ test result on FT2. This was repeatable. Two pair armoured feed. It was on the green/black already. Passed the PQ well. I tried a single ended test of the orange/white failed, small earth, very low A/C.
At the UG radial DP, it would test 100% OK, time after time.

Interestingly, I tested on FT2 to the 66 again, and then it was ‘potential HR’


Strange stuff.

Yes, that’s part of Openreach’s network.

I say get it reported, the engineer will be able to get up to the eaves and dis off the rogue wiring .... your set up is ‘star wired’ before the NTE.

The question has to be, who installed it? Was it an original BT or even GPO or a previous tenant/owner?

From a joint at the eaves ? Almost certainly not Joe Public. Too much effort.

Back in the day it was done a lot , but never the right way.

Do you come across man xNTE fitments?

That design, without a built in filter, was a bit of an own goal for OR? A bridge tap by design.

I remember seeing a picture and a description and wondered how a broadband filter could be implemented....

Cheers!

Domestic bridge-tap installations probably weren't a factor in the days of morse code and telegrams . Or even the pre-xDSL data transmission days.

I’ve come across plenty ... rolled out when ‘we’ already knew better. Bypass and fit an NTE on the first point in.

Sadly Bob, they were very much well into ADSL days.

Out of curiosity, does the fact the observed speed being below the handback threshold mean this is something to act upon here?

It depends on your home wiring.

If that is optimised and there are no problems with your kit or wired connections, (loose or damaged ethernet cable or socket), and it isn't a speed test over wifi, probably yes.

If it is sub-optimal and Openreach come out and diagnose, (not necessarily fixing it in some of those cases), you are almost certain to get a bill of over £100 from your ISP, as Openreach will bill them as not their problem. Though at the moment OR probably wouldn't be interested at the moment as it, (normally but not in the case of a joint under the eaves), needs access to the premises.

In this precise case, of a bridge tap outside the premises in a location where it is unlikely to be a DIY-caused problem, it should be as Zarjaz recommended. Openreach to fix FOC.

In reply to a post by partial:

>>The only time I can think that there would be a bridge tap in the network ...

As with many things there will be regional differences.

In my manor there are quite a few exchanges that have some teed up local main cables. One bar pair feeding 2 different cabinets. In some cases cabinets being a couple of km apart!

There are also frames that were condensed / moved and the old frames left teed in in the cable chamber or manholes close by. I had a contract to recover the tees on one of the largest exchanges in the UK a year or two back.

Interesting. But that wouldn’t affect the test result for the FTTC. Did you ever see similar on the D-side? Only example I could think of was a cabinet changeover.

In reply to a post by Zarjaz:

I’ll take your word for it. I never once saw that myself.

I was incredibly confident in that “bridge tap” test result whenever I saw it even if I couldn’t find the actual culprit sometimes, maybe it was buried behind a wall or that sort of thing. If I couldn’t locate it I’d run a new lead-in entirely straight into the master socket and that would then return a normal test result.

I used to be like you ... had heard a couple of colleagues claim they’d had it, but I was very dubious myself.

.. but, about three weeks ago, had exactly this . You could fit an NTE on the UG pair in the 66, put your tester in sync, and get the ‘bridge tap’ test result on FT2. This was repeatable. Two pair armoured feed. It was on the green/black already. Passed the PQ well. I tried a single ended test of the orange/white failed, small earth, very low A/C.
At the UG radial DP, it would test 100% OK, time after time.

Interestingly, I tested on FT2 to the 66 again, and then it was ‘potential HR’


Strange stuff.

Always interesting ones those, odd result at the BT66 compared to the DP. Has to be some kind of buried joint, you’d think?

Edited by deleted (Wed 08-Apr-20 08:01:05)

Has to be some kind of buried joint, you’d think?

I’m not so sure, maybe just the cable pinched UG somewhere, so making a contact with the 2nd pair ?
Have since heard from a colleague who had the same issue on an overhead fed property, ‘potential HR’ at the eaves, good at the DP ... a replacing the DW fixed that.

No I think of it , my ‘contact with a spare pair’ theory might hold good for that too, if the original was DW10 or CAD55 maybe ??

In reply to a post by Zarjaz:

Has to be some kind of buried joint, you’d think?

I’m not so sure, maybe just the cable pinched UG somewhere, so making a contact with the 2nd pair ?
Have since heard from a colleague who had the same issue on an overhead fed property, ‘potential HR’ at the eaves, good at the DP ... a replacing the DW fixed that.

No I think of it , my ‘contact with a spare pair’ theory might hold good for that too, if the original was DW10 or CAD55 maybe ??

Our line has shown a bridge tap on occasions, also the problem sometimes relates to rainfall(but not 100%) so I'm wondering if this relates.

In reply to a post by burble:

In reply to a post by Zarjaz:

Has to be some kind of buried joint, you’d think?

I’m not so sure, maybe just the cable pinched UG somewhere, so making a contact with the 2nd pair ?
Have since heard from a colleague who had the same issue on an overhead fed property, ‘potential HR’ at the eaves, good at the DP ... a replacing the DW fixed that.

No I think of it , my ‘contact with a spare pair’ theory might hold good for that too, if the original was DW10 or CAD55 maybe ??

Our line has shown a bridge tap on occasions, also the problem sometimes relates to rainfall(but not 100%) so I'm wondering if this relates.

It really was just a thought that struck me as writing that last reply. Is your line OH or UG ?

In reply to a post by Zarjaz:

In reply to a post by burble:

In reply to a post by Zarjaz:

... nested quotes trimmed ...

I’m not so sure, maybe just the cable pinched UG somewhere, so making a contact with the 2nd pair ?
Have since heard from a colleague who had the same issue on an overhead fed property, ‘potential HR’ at the eaves, good at the DP ... a replacing the DW fixed that.

No I think of it , my ‘contact with a spare pair’ theory might hold good for that too, if the original was DW10 or CAD55 maybe ??

Our line has shown a bridge tap on occasions, also the problem sometimes relates to rainfall(but not 100%) so I'm wondering if this relates.

It really was just a thought that struck me as writing that last reply. Is your line OH or UG ?

Our line runs under ground to the pole, the chamber next to pole fills with water in wet periods, and has to be bailed out for any work to be done!

But a wet joint would usually give you a battery contact fault, this would easily show on any testing.
If my (half arsed) theory is right, it would need actual metallic contact with a spare pair.

In reply to a post by RobertoS:

Domestic bridge-tap installations probably weren't a factor in the days of morse code and telegrams .

There were actually! When i was first at sea, 1977 communications to/from home were mainly by letter to from the next port (no mail drops from aircraft like North Wales Police tried to suggest to my father!) No satellite on the ships that I was on, so at sea it was either Morse telegram or a Ship Letter Telegram which was posted rather than Telegram delivery or HF radio telephone.Even telephoning from ashore could take hours for a connection from Central America to UK. Problem from ship was that the UK only had about 6 telephone channels in total and in 1977 there were a lot more ships than there were in later years. So if you wanted to phone from say south Atlantic, you called BT's Portishead radio immediately after they had concluded with another ship and you were given a Turn or a QRY as it was known as. When your turn came, after exchanging details of the telephone number and the ship's charging authority, Portishead Radio attempted to put the call through. If the line was engaged, they could if they were not too busy, interrupt the ongoing call and connect the ship. If too busy to waste time, you would go back into the queue. It could be a drawn out process.

Anyway, heard from home in a letter that BT were going to make our telephone line a Party line. This because our next door neighbour, the only house out of the 57 that had been built in 1973, did not have a phone line. So we ended up as a Party Line with the house opposite - all three houses plus other fed from the same pole. I found this strange, since when the house was built, we had to wait for telephone lines to be laid from the local exchange a couple of miles away and I would have expected the cables to have had sufficient capacity. Being a party line increased the chances of our number being effectively engaged and prevented Portishead Radio from interrupting a call in progress.
When I eventually arrived home, spoke with BT and they were a bit surprised that the neighbour wanting the phone was not on a party line. Not long after our line was reverted back to a normal line.

So there we have it, a Bridge Tap causing telephony problems

On a technical note, there was no suitable place due to a solid pathway around our house, for an earth rod to be installed for the ringing current and identifying which party wanted to dial out by pressing the Party Line button, so the electricity earth was used. Not ideal?

Strangely, a few years later, I wanted a second line installed and this was done within a couple of weeks without to my knowledge any one having to go on a party line.

Despite the distance, both lines could give full speed on a V.90 56K modem - wow that was fast!

Cheers!

Party lines.
I remember those, and having to press the button.

That would have been when we lived in Blackpool.