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Diagram of How BT’s New FTTrN Superfast Broadband Technology Works

Monday, September 1st, 2014 (2:32 pm) - Score 18,639

After several weeks of pestering BTOpenreach’s poor communications team, we’ve finally managed to extract a simple diagram to help illustrate how their new Fibre-to-the-Remote-Node (FTTrN) technology will work.

As first reported back in March 2014 (here) and then again in an update last week (here), FTTrN is similar to BT’s existing ‘up to’ 80Mbps capable Fibre-to-the-Cabinet (FTTC) technology. But where FTTC takes a fibre optic cable from the telephone exchange to your local street cabinet (your existing copper line is used between the cabinet and homes), FTTrN sees the fibre optic cable being taken to a significantly smaller ‘Remote Node’.

The nodes effectively act like tiny street cabinets, except they can be positioned on nearby telegraph poles or inside manholes etc. Several advantages can exist with this approach, such as the ability to avoid the need for building a new street cabinet in areas where this may prove difficult or expensive to achieve.

In some areas it may also bring the fibre optic cable much closer to homes, which can result in faster and more stable service speeds. Furthermore some nodes can be powered by the home itself (reverse power), although so far as we can tell BT are likely to stick with their existing remote power setup (i.e. they supply the power for your copper line to work). The network diagram is shown below.

fttrn network diagram v1 ispreview edited

BT’s trials are designed to help the operator understand a variety of difficult factors, such as the costs of deployment and maintenance, as well as the impact on performance and time to install. As a result the trials aren’t just taking place in rural locations like North Yorkshire, but also London’s Shoreditch area and a small part of Bedford town.

Ultimately FTTrN won’t work everywhere and if you can already get a decent FTTC or even FTTP service then the chances of getting FTTrN installed are pretty remote. Instead BT currently sees this service as being one with the potential to fill those awkward urban and rural gaps, where their existing approaches might be less cost effective.

This stance may or may not change in the future, especially since to get the most out of next-gen technologies like G.fast (aka – FTTC) you really need to bring the fibre optic cable even closer to homes. But it’s difficult to see a cost conscious company like BT going back to existing FTTC areas in order to achieve that. Time will tell and finding the answers to such questions is one of the reasons why you run such trials.

Leave a Comment
70 Responses
  1. Avatar Pedrostech says:

    The equipment shown in the top pic seems to be fitted on a number of poles near my house and I’m nowhere near those trials. Could this be the way that Superfast Surrey’s web checker thinks I’ll get broadband despite being too far from the cabinet:?! We shall see.

    1. Avatar DTMark says:

      Are the boxes on the poles black?

      If so they might be DACS boxes. Many of the poles round here have those.

      Nothing to do with broadband, indeed the antithesis of DSL broadband.

    2. Mark Jackson Mark Jackson says:

      Ignore the top left pic, that’s just the closest match I could find and is not an exact FTTrN representation.

  2. Avatar Pedrostech says:

    @DTmark-nope, they’re not DACS. The main thing is the cable, there’s the black cable with the yellow stripe as in the pic. It’s only on the telegraph poles covering those I predict to be too far from the cabinet.

    1. Avatar MikeW says:

      The yellow stripe suggests it holds fibre. If the enclosure that the cable enters looks exactly like the one in the photo, that would be a fibre manifold, used to connect the final drop BFT into the home.

      That, in turn, would mean they are preparing some form of FTTP.

  3. Avatar Raindrops says:

    So this is as expected basically FTTH minus the last few metres of the drop wire. Seems a waste of time to keep that last few metres of copper. Still i spose it allows for more milking of copper line rental.

    1. Avatar Gadget says:

      Also allows for all the services not compatible with fibre delivery and the ease of plugging in any existing analogue ‘phone

    2. Avatar TheFacts says:

      It’s not a few metres and there is the cost of getting the fibre into many different types of properties. Plus do all the ISPs have a router with battery backup as required by Ofcom for 999 access?

    3. Avatar Raindrops says:

      The copper line already going to the home would have all that regardless.

    4. Avatar GNewton says:

      @TheFacts: The finisted of British ‘Can’t Do’ culture expressed here 🙂

    5. Avatar Raindrops says:

      I think he was just coming up with more poor weak excuses rather than thinking logically that a copper line is already there whether you do FTTH or not for things like 999 calls.

      You have to remember BT employees do not think the just randomly speak.

  4. Avatar hmmm says:

    probably another failure with the bt openreach clowns

    1. Avatar TheFacts says:

      Please expand on this comment.

    2. Avatar GNewton says:

      Why should he? It is very obvious to most users that BT is a failure when it comes to provision of genuine fibre broadband services. What makes you think BT is a succes story? It’s one of the worst compnies to deal with in the UK.

    3. Avatar TheFacts says:

      When people want to pay £1.75/month plus line rental it does not leave a lot for investment. That’s the real issue.

    4. Avatar Raindrops says:

      What investment rurally? I thought thats what government funds was used for.

  5. Avatar fastman2 says:

    hhhm — another postive comment !!!!

  6. Avatar fastman2 says:

    FTTRN open cvers around 16 customers at max so will be ideal in small rural hamlent where around 15/20 customers at max

    1. Avatar MikeW says:

      Do you know what the DSLAM is?

      The original ECI MiniCab 64V (which looks slightly different to the DSLAM in Mark’s picture) was being touted for this job a while back, but not confirmed AFAIK. It would support 64 ports.

  7. Avatar Patrick Cosgrove says:

    Has it been approved for Phase 2 BDUK rollout yet?

    1. Avatar MikeW says:

      Approved by whom? Central BDUK, BT or individual LEAs?

      The original pilot in North Yorks is still continuing, as part of the phase 1 works – and that appears to be all that has been approved by the council as yet.

      SFNY has approved spending their phase 2 funds with BT under the existing contract, although those funds are part of phase 1 BDUK, not SEP. However, the project needs to report trial results to the council to say whether FTTRN will be included in phase 2 (giving an extra 5,000 properties at superfast speeds); this allows the council to make decisions about who to spend their phase 3 (SEP) funds with.

      SFNY were due to report something on the phase 3 plan to the council executive next week, but this seems to have been deferred to a later date.

  8. Avatar FTTH says:

    FTTRN is an Old technology, it has been used in South America quite well.
    (Check companies like Adtran).
    We looked at it about 6 years ago, but the fact that it needs powering and was the size of a small suitcase was a roadblock.

    They will work well for small rural areas, cascade them on a GPON network cost effectively and you can eliminate cabinets.

    BUT – The units can land GPON feeds and handoff VDSL.

    So Why not just distribute the PoN?
    It will be cheaper, no question.

    Possibly this is stage 2 of the BDUK plan, then stage 3 will be replace all the copper with fibre as the trunks and feeders will then be in place. All with handouts of course.

  9. Avatar gerarda says:

    BT need to get a move on if this is their only solution to ensuring the USC in the BDUK contracts, some of which require this to be done by the end of next year.

    1. Avatar MikeW says:

      Why do you think of it as a USC solution?

      While it obviously has a side-effect of improving USC coverage, it is very much a solution for getting superfast speeds to more premises.

      Sited 1000-1200m from the existing cabinet, it extends SF range another 1000-1200m. If Sagentia is correct on D-side lengths, that gets SF coverage from 90% up to 99%.

      Why the only solution?

      Certainly satellite is considered as a solution for some properties, so there is at least one more possibility.

      If this *were* the only solution for USC, I’d have expected it to include ADSL2+ functionality, to take advantage of the extended range that ADSL2+ has over VDSL2.

      (Saying that makes me think that NICC approval is needed for *any* kind of FTTRN device, VDSL2, ADSL2+, or NGA-Amplifier)

      End of next year? Some projects need it by the end of *this* year!

      Unless, of course, they negotiate around it as part of phase 2 funding. SFNY has already shown that USC budgets & timescales are a part of the negotiating strategy, so are open to change.

    2. Avatar gerarda says:

      I think there will be a lot of very peed off village council tax payers if it turns out their money has been spent to provide them with a satellite service. Perhaps a solution for the odd isolated property but not for the bulk of the USC requirement.
      What else are BT trialling that would have this reach and so solve the USC issue? I have not heard of anything. They have made noises about wireless but have seen no action on this.

    3. Avatar MikeW says:

      The contract for North Yorks allows for properties to have to resort to satellite, but limits the number to a maximum of (IIRC) around 3,800. That would be 1% of the county, or 2% of the intervention area.

      As last reported, SFNY were investigating the impact of removing that upper limit – presumably to find out how much of the USC budget could be shifted over to the SF side if more USC subscribers were pushed onto satellite.

  10. Avatar MikeW says:

    Mark – Thanks for digging further in this. It makes for interesting examination.

    The pictured “Hybrid closure – PCP position” looks suspiciously like it contains splice trays, including colour-coding that suggests a splitter node. That is promising for future fibre deployment in the area.

    The “copper interception point” suggests that this is still a way from being FTTdp – that there is still some unknown portion of the D-side wiring in the loop on top of the final drop.

    The label of the closure makes me wonder another point: does it turn the set of plain joints in a chamber (for example) into a fully-fledged PCP interconnection point?

    Funny how each snippet of information just generates more questions…

  11. Avatar NGA for all says:

    It’s looks great, any indicative cost per install, this needs power, I assume someone will set a limit on the power cost, so the FTTP V FFTrN should be easy to calculate.

    1. Avatar Raindrops says:

      The customer from as the tech stands would pay the power bill from my understanding.

    2. Avatar NGA for all says:

      G.FAST standard, My understanding the powered from the home. Rn has a small dslam attached to the pole which suggests it needs power.


    3. Avatar Raindrops says:

      Good spot NGA for all. I wonder how they intend to get power to it?

    4. Avatar FibreFred says:

      Does G.Fast require more power than a VDSL2 DSLAM? If they can power a DSLAM without the need for the customer to power it can they not power the G.Fast kit in the same way?

    5. Avatar No Clue says:

      I think the question both should of asked is more IF (as its unknown) BT are powering that DSLAM on the pole then how are they powering it?

      Poles AFAIK do not have their own separate power feeds/supply running to them.

      Power that comes down a copper phone line is also not reliable and fluctuates line to line (ive previously had to have a pairs change due to low power on a line). So i doubt they are drawing power like that.

      The only thing i can think is when they run the fibre to the pole they also run the power lines required (like you would to a cabinet), but that to me would seem a bit silly as you are basically then running another long cable (ironically probably copper) to supply power.

      That not only seems counter productive but surely jacks up the cost significant over just being able to run a fibre cable.

      I guess more information if it ever gets out of trials will be needed.

    6. Avatar Raindrops says:

      It was a good spot by NGA for all, i did not notice. Certainly would be interesting in HOW they get power to the thing if they do at all.

    7. Avatar MikeW says:

      Micro-nodes for VDSL2 so far seem to offer the option of local power, or to be “remote powered” from a previous node (like the FTTC cab or exchange) over standard copper pairs, and probably at the (fairly standard) 48V used by telco kit. For example, the ECI MicroCAB 64V will accept 240V or 48V, and can be powered by ECI’s remote-line-powering technology using 12 pairs. The maximum power consumption is 170 W.

      Such forward-fed remote power does need enough spare pairs in the D-side, but as this is a trial, BT can easily pick a location where this is true.

      Reverse-power, from the subscriber, is a feature being worked on for FTTdp micro-nodes running G.Fast. It seems like the ETSI standard for reverse power is in a good state (mostly approved in April 2014) – but keeping the power consumed by the G.Fast chipsets low enough for this to work is a problem taxing a few companies. Certainly there are features within G.Fast to allow for low-power states when there is no data to send, and they seem to be working on ways to make sure that power consumption is split fairly amongst the subscribers, taking account of the different line losses involved. There are plenty of other challenges in this area, too.

      I’ve seen a reverse-power presentation where the power output from the CP end is either 20W or 30W per line, getting around 15w or 20W respectively through to a node that is 250M away. The same document assumed that a G.Fast application consumed 20W for 2 lines, while a VDSL application consumed 16W.

      Right now, the concept of reverse-power is being back-ported towards the VDSL2 micro-nodes, and VDSL2 chipsets being reworked to reduce power consumption, and presumably to cope with the cases where most/all subscribers turn their power off. We should expect to see these products available soon… but soon enough to trial right now?

      So who knows. BT could be trialling a reverse-powered node for FTTRN, but I wouldn’t rate the chances too highly.

      There is even the possibility of power-over-fibre. I don’t think this can deliver enough power for what we want though.

      But it will certainly be true that the cost per home will be considerably cheaper if they don’t have to provide local power, or have to run extra (new) power lines in parallel with the fibre.

    8. Avatar No Clue says:

      Still does not explain how this is being powered or the costs involved or how they get power to a node.

      You can not power it using the standard phone lines or rather should not for numerous reasons. Voltage varies line to line in this country which would mean some nodes would need more lines to power it than others. Even if it did not you can not bundle voltage from multiple lines to power the thing (run in what is called series), or rather that would be a stupid solution. If one line fails it means power failure to the FTTrn equipment people would be connected to. Some poles even if you wanted to power it via the copper lines going to the pole you could not because the pole may not have enough copper lines going to it in the first place.

      Likewise taking voltage from other lines to power the thing will affect lines that do not have a FTTrn broadband service. xDSL will only work reliable if the line is above a specific voltage. When i had ADSL my line would disconnect all the time (every few hours), when i upgraded to FTTC they actually had to change the pairs i was on just to get it to connect. The engineer at the time actually had a bit of a whinge about it and said it should had been fixed when i was on ADSL and had called them out previously over broadband faults.

      This is no different really to how overhead power lines work or power lines for a train work. You do not even attempt to power the whole network all in one go you set it up in phases and sections, each stretch having its own power supply (thats what all the copper cable that gets nicked from railways normally is and those little hut like building with high voltage symbols on them) see if one stretch fails the rest does not. To do the opposite of that would be idiotic. It would affect other services, be a totally unreliable way to power those that have FTTrn and in general be nothing but trouble. Im not even sure what you mean by cabinets and how you describe cabinets are powered, they each have their own power.

      The only sensible way to power this is either each user powers it thereself, which would turn me off straight away. Or BT power each node individually and to do that reliable you either need spare power cabling or you need to lay your own.

    9. Avatar MikeW says:

      You are right on this point – we don’t know what BT are doing. Everything that *any* of us writes here is conjecture.

      However, remote power, using many copper pairs in parallel, is a fact.
      – ECI Telecom have their own solution (“remote line powering”) that can be applied to their MiniCAB 64V, and obtained a patent on the principle in 2002. 12 lines
      – Swisscom are using the technique in their current VDSL2 FTTS solution (IIRC, using Alcatel’s micro-nodes); up to 8 lines.
      – Aethra have a line of products whose sole aim is to provide power for remote cabinets (though they are aiming at larger cabinets, rather than the micro ones); this solution uses 7 lines plus 3 backup.

      Whether BT will go ahead and use anything like this is another question; they might not like high voltages on their copper at all.

      When I first had ADSL installed (in the very first months it was being trialled), the engineer told me that the lines were powered at a higher voltage than normal; their plant database was set to highlight in red any cable bundles that carried lines with these higher voltages; I assume the higher safety risk makes maintenance a little harder.

      Aethra’s product:

      Swisscom’s usage in FTTS (page 13):

    10. Avatar MikeW says:

      One from Alcatel (page 5)

      This one really looks at G.fast, but it lists pros and cons of both remote power and reverse power.

    11. Avatar Raindrops says:

      “However, remote power, using many copper pairs in parallel, is a fact.”

      Using multi lines to reach a required voltage is running things in series as No clue describes.

      To run things in Parallel the voltage on all the lines would need to be the same and for UK phone lines AGAIN as No clue mentions that is not the case.

      Running things in Parallel also leads to further voltage drops, this is all simple to understand basic electricity…..

      Series and parallel are not the same.


    12. Avatar MikeW says:

      Oh dear. This is so wrong, I don’t even know where to begin, except for wiping the coffee out of my keyboard. But lets start with the fact that I’ve understood the difference between parallel and series circuitry for 40 years.

      You did read the links I provided, didn’t you? The patent *shows* you links being used in parallel.

      1) Using multiple line pairs is providing power in parallel. Not series, although you could indeed contrive a circuit that wound back-and-forth in a series style. But you just wouldn’t do that.

      One pair would provide, say, half an amp. If you want two amps, you’d need 4 pairs.

      In this kind of power system, the line pair is, essentially, a long resistor. Half the resistance is encountered on the A-leg on the way out, and the other half of the resistance is encountered on the way back (so one pair does act with one wire in series with the second wire, but this is the only point where “series” is involved).

      Using multiple lines connected in a simplistic way, you end up with multiple resistors in parallel. All the A-leg resistances are connected in parallel, and all the B-leg resistances are connected in parallel.

      Connecting resistors in parallel reduces the overall resistance, and increases the total current that flows. That increases the power.

      A simplistic connection of the multiple lines is enough if the losses/voltages were the same, but they are not (both you and No clue are right on this). So to deal with differing losses/voltages, we move onto…

      2) The lines do not have to provide the same voltage. After all, you are both suggesting that reverse power will be used here – and that too will provide different voltages from different length lines. The same problem has to be solved in both designs (*)

      To cope with different voltages, what you need is enough circuitry at the remote end to isolate the lines, but that is easy. A transformer does that kind of isolation. Once isolated and transformed (using an AC transformer or a DC/DC converter), the output voltages *can* be combined.

      Look at image 1 of ECI’s patent: That shows 3 lines in parallel, with the right kind of isolating circuit at the far end, using a switched transformer, and described in the text. The word “parallel” appears once in the patent itself – saying that the whole apparatus can be repeated & combined in parallel to increase the output power. Then “Each apparatus … may aggregate power from, for example, 16 line pairs.”

      3) In the general case, “running things in parallel” doesn’t ever lead to further voltage drops. Adding resistors in parallel to other resistors will decrease the overall resistance and increase the total current, but the voltage will remain the same. That’s at least true when these resistances are the only things in the circuit.

      Add more of a load in addition to the resistors, then you are more likely to find that the other load constrains the increase in current, meaning that the voltage drop (over the resistors in parallel) is actually likely to reduce, not increase. But that depends very much on the rest of the load.

      As you say, simple electronics. Simple application of Ohm’s law.

      4) (*) Reverse power for FTTdp works by collecting power off subscriber lines in parallel in the same way, with the same problem: Near lines (10m) will suffer little voltage drop, around 0.3V, while longer lines (250m) suffer a greater drop of 8V.

      There’s a presentation by MicroSemi on reverse power for FTTdp which details several issues on this front; on page 7 they show a block diagram for 8 lines providing power in parallel. You can note that it too depends on isolating ciruitry, though in this case it is labelled as an “Isolated DC/DC” converter.


      They even have a section on “FairPower”, where they mention that they can adjust the power taken from each line, by adjusting the load on those lines, so that the end-users all pay for the same amount of electricity.

      Why bother inventing “FairPower” if it is impossible to extract power from those lines in parallel? Or if you must require that they all have the same losses?

    13. Avatar Raindrops says:

      You can not run any circuit in parallel if the power from the “parallel” part of the circuit is not the same. BT line voltages vary. You can type as much as you want you will not break the laws of physics or alter the fact all you links assume lines are equal which BT are NOT……

      This is parallel

      This is series

      The only one you can run if your source volts vary is SERIES.

      BT could do this as a solution…….

      But thats more cost.

      PS….. Good to see you still replying but not knowing what you are on about.

    14. Avatar No Clue says:

      Raindrops Those charts and descriptions show nicely why a parallel circuit would not work nicely. The best is http://www.autoshop101.com/trainmodules/elec_circuits/circ127.html which shows EXACTLY what BT would likely have to do as the cheapest possible solution if they want to use the phone lines for power. I am not sure what Mike means when he states….
      “One pair would provide, say, half an amp. If you want two amps, you’d need 4 pairs”
      That would be a series circuit not a parallel one. As has also been pointed out to him power varies line to line here in the UK so it would not be that simple.

      The other issue using that “”One pair would provide, say, half an amp. If you want two amps, you’d need 4 pairs” example is if a current pole has say 10 lines and 8 of those lines have a form of ADSL or other variation of broadband already that means you have 2 lines free for power but need to find another 2 lines (using his example).

      You can not just take the extra power from 2 lines with ADSL services. Even ADSL requires certain power requirements on the line to work reliably, so you cant just nick the power from those lines. I doubt you could nick it from lines that only have a telephone service either, if voltage is too high or low on them you get weird issues with the phone chirping (i know from my low power on the line i had).

      It may also be worth him reading up on something called ohms law to understand voltage and circuits which he refers to because he has not. Using a multiple of anything be it batteries, telephone lines etc to reach a certain (normally higher) voltage to power something is a series circuit. Nearly anything you put batteries in like say a motorised toy car is a SERIES circuit. The motor in the car needs 5 Volts, and the car takes 3x 1.5 Volt batteries to give it that 5 volts.

      Connecting multiple batteries (or phone lines) in parallel would actually mean losing power not making full use of its grand total.

      And finally just to show his statement makes no sense….

      The bottom part with the diagram of 2 batteries of a 6 volts shows nicely why lines of a fixed power and combining that power in parallel as he describes wont work. IE You need 12V you connect 2x 6volt supplies, you end up with 6 volts in a parallel circuit, to combine the power you use a series circuit. The batteries will last longer with the parallel circuit but the wont give the needed combined 12 volts.

      All very easy to understand.

    15. Avatar TheFacts says:

      You are ignoring the technology such as DC/DC converters taking defined amounts of power from each line. This takes account of different line characteristics.

      It’s not like connecting some batteries and light bulbs.

    16. Avatar No Clue says:

      Nowhere does that link explain how you run anything in parallel to output more voltage than what an individual supply has. It also shows nicely via a diagram right at the top it is UNUSED copper pairs used for power. Again something else i went over and explained why you cant just grab power from any old line.

      So unless BT shove a node up a pole with lots of UNUSED spare pairs it does not stand a chance regardless of Series Vs Parallel arguments of being powered in that manner. The pole in my road after my pairs change has exactly 1 free pair left….. The low power one i originally had, so NOPE powering it that way in my street and more than likely many others up and down the country will not work.

      You can not re-write science much as it appears BT fans believe you can to try to suit their arguing.

    17. Avatar TheFacts says:

      See slide with ‘multi-line RPF extraction’

      multi-line reverse power feeding.

    18. Avatar Raindrops says:

      Chart on Page 5 shows to use existing copper lines for power they have to be unused copper lines.

      Page 6 or the ‘multi-line RPF extraction’ clearly shows power (The green line that runs back to a on a separate circuit with the customer feeding it.

      Page 11 and the more detailed chart titled ‘RPF FUNCTIONAL REQUIREMENTS IN DPU’ shows this with the PSE on the right graph titled ‘Customer Premises Equipment (CPE)’. Page 17 further confirms this. Anything in a grey outlined box on that document seems to refer to customer side equipment in every chart, stuff not in the grey outline box is not customer end.

      So your document shows exactly what we have both said, you CAN NOT use current phone lines which are in use for power, they have to be unused. As per page 5.

      Along with an example of the customer and not the provider powering it.

      It shows nothing to show a provider powering anything in Parallel either. No clues link of http://tech.texasdi.org/seriesandparallel shows exactly what the difference between the 2 circuits is.

      I imagine BTs current 3 house trial it was pretty straight forward as even the story mentions it was ran separate from other BT plant, this as a full product though they either A) need a load of unused pairs B) Run stuff in SERIES but risk one failure taking out power to many, or C) The customer powers it. Knowing BT they will end up going with option C, the cheapest for them, as they always do.

    19. Avatar No Clue says:

      Yeah page 6 basically shows PSE (power SOURCING equipment in case he didnt know) in the customers home which then almost runs in a loop back to a supply which then distributes the power to others in the network. Its similar to how PoE works. Using that method would mean the customer is the original source of power. They would all be like solar panels on your roof each one feeding a small amount of power back to a bigger supply which then distributes it. Again technically speaking its a parallel circuit, just with switching in it.
      The other concern if they go that route is DC is far less efficient than AC due to lower volts, though that may be of benefit depending on how many like drones (sorry customers) they have hooked up powering it.

    20. Avatar Raindrops says:

      “Again technically speaking its a parallel circuit, just with switching in it.”

      You mean series, surely?

    21. Avatar No Clue says:

      Opps yes meant series.

  12. Avatar MikeW says:


    You’re just not getting it. *None* of your example pictures gives a good example of how power is delivered for remote-powering.

    You need a picture with one battery (ie one source), one bulb (one load). Then have multiple wires from the +battery terminal, all going to one side of the bulb. And have multiple wires going from the other side of the bulb all to the -battery terminal. They are long lines, where each acts like a discrete resistor, so could be pictured that way explicitly.

    Shall I draw some pictures?

    1. Avatar No Clue says:

      No you are not getting it because if it is reversed powered that will be more than one source of power (PSE) from EACH customer. If its power by BT then there would be multiple bulbs (except in this case its the nodes on poles) which are being powered in the circuit AGAIN from multiple sources. Unless you now think exchanges have just a singular big almighty PSU?.

      If you can not understand something in series combines and normally ups voltage output while something in parallel combines power but the voltage never exceeds the maximum of multiple supplies then clearly you are not as familiar with ohms law which you initially bought up.

      You do not need to draw a picture plenty have been provided to you. Plenty of explanation with the pretty pictures have also been provided to you on what both circuits do.

      Then again obviously because you like to think myself and a choice other few posters are always wrong, science, physics and the internet is now also obviously wrong now. In your opinion for what little it is worth.

      Its ok to be wrong (i made a mistake and was corrected), continuing to be wrong and repeating your mistakes though just makes you a bigger mistake.

    2. Avatar No Clue says:

      PS are we going to have fibre dred join us this weekend, or one of his other scitzoid personas again?

    3. Avatar MikeW says:

      @No Clue

      My part of the discussion concentrates on remote powering, ignoring the reverse power from consumers. We can come back top that later if you wish.

      I understand that putting voltage sources in series results in adding their voltages, but not the current. Using P=(V*I), the increased V means increased power.

      I understand that putting voltage sources in parallel results in increasing the available current, but not the voltage. Using P=(V*I) again, the increased I means increased power.

      As I said, the existing pretty pictures do not show the picture we need. There is no point showing a system involving two bulbs as an example of either series wiring or parallel wiring because we are talking of a case where there is a single load (if there are 2 nodes, they are powered by separate sets of pairs). There is no point showing examples of two batteries either, in series or in parallel because, again, that does not show the true picture.

      In the picture we want, there are only multiple wires.

      What do you think an exchange is powered by? It is probably more complicated than you think.

      Usually it is designed to be powered in parallel by:
      – Mains power, rectified & smoothed down to ~51V
      – An almighty lead-acid battery bank, with cells connected to make 48V DC.
      – Optionally, a generator that trips in when mains fails.

      The main power is designed to be always on, and in this state, it both supplies the main load and float charges the lead-acid batteries all the time. If mains drops out, the batteries start providing the power instantly, without any gap. Service continues.

      However, once the exchange starts drawing current from the batteries, the voltage from the batteries usually drops somewhat. To counter this, the power is fed into DC/DC converters to keep a equipment fed with a consistent voltage at all times.

      The output from these DC/DC converters are the feeds into all the cabinets of the exchange – and are the source of all those -48V lines to every properties. The DC/DC converters, that bring the power sources together, are indeed one big PSU.

      Here is an example of a 400A power system used for AXE-10, Ericson’s digital exchange sold worldwide in both fixed and mobile networks. In the UK, it has been used by BT (where it is known as System Y), Vodafone and T-mobile.

      See pages 13-21 of:

      That is early 80’s technology, with a 40 year lifetime. It is the kind of equipment that will have been available when BT started installing System Y in their network.

      Here is another example from Ericsson from the late 80’s. See pages 7-13:

      This kind of equipment tries to perform a more modern charging regime on sealed batteries, and is the kind of equipment that was available when Vodafone & T-mobile were installing their GSM-based networks. It is also a reminder of the state of equipment in our development labs back when I worked on those GSM networks.

    4. Avatar MikeW says:

      Here’s an old battery room.

      The thick copper busbars bring back some memories of seeing these run along the ceiling above an exchange. I’ve heard a story, apocryphal or not, of someone dropping a spanner across such busbars. Ouch.

    5. Avatar MikeW says:

      Just on the topic of parallel vs series, I’ve done a series of pictures to show how multiple wire pairs are used in parallel.

      Take a look – there are 8 pictures, set out in a logical procession.

      Let me know the first (just the first) place where you disagree with the progression.


    6. Avatar Raindrops says:

      “I understand that putting voltage sources in parallel results in increasing the available current, but not the voltage. Using P=(V*I) again, the increased I means increased power.”

      Err no, CURRENT is affected by either voltage or resistance. If the voltage is high or the resistance is low, current will be high. If the voltage is low or the resistance is high, current will be low.

      “As I said, the existing pretty pictures do not show the picture we need. There is no point showing a system involving two bulbs as an example of either series wiring or parallel wiring because we are talking of a case where there is a single load (if there are 2 nodes, they are powered by separate sets of pairs). There is no point showing examples of two batteries either, in series or in parallel because, again, that does not show the true picture.”

      The amount of bulbs does not matter its how its wired that determines if a circuit is parallel or series. The power be it a batteries or PSE also makes no difference unless one is AC and another is DC, you could substitute the battery in those diagrams for a DC PSU it would be doing the same thing. Likewise one bulb, 2, 3, 4 makes no difference.

      Look at the bottom left image…….

      This concludes that you have no idea what you are on about.

    7. Avatar MikeW says:

      Well, doh. If you wire one set of components in series, it is obviously called series. That’s real hard to figure out.

      The problem here isn’t about the components – it is about the wire between them.

      Using multiple pairs is all about using multiple wires between components, not about having multiple components.

      Concentrate on the wire.

    8. Avatar No Clue says:

      Id give up raindrops he clearly does not understand circuits and even if he did he has now moved back to powering it via multiple lines argument, which has already been rendered mute as the lines would need to be unused.

      Nice call out on his lack of understanding ohms law also.

    9. Avatar MikeW says:

      I agree – the lines from the exchange direction need to be unused. Spare. I haven’t once said otherwise.

      Let me know when you’ve read the slides I did for you. Then we can concentrate on how Ohm’s law applies there.

  13. Avatar MikeW says:

    On batteries being put in parallel, you are wrong. It *does* make more current available to the circuit. And thus @NoClue is wrong to congratulate you.

    Take a look at figures 1 and 3 here:

    or this page

    You might like to consider that batteries have an internal resistance. Putting batteries in parallel (like putting plain resistors in parallel) reduces the overall resistance, and allows higher current to flow.

    Fortunately, while I know Ohm’s law, I also know a *lot* more than just Ohm’s law.

    1. Avatar Raindrops says:

      On batteries being put in parallel, you are wrong. It *does* make more current available to the circuit. And thus @NoClue is wrong to congratulate you.

      Take a look at figures 1 and 3 here:http://batteryuniversity.com/learn/article/serial_and_parallel_battery_configurations

      No he is not……

      Ill repeat…
      “CURRENT is affected by either voltage or resistance. If the voltage is high or the resistance is low, current will be high. If the voltage is low or the resistance is high, current will be low.”

      As he said he knows what ohms law is where as you don’t.

      Moving on to your latest link, it appears you have you figures messed up again.
      FIGURE ONE is a SERIES circuit which increases voltage.
      FIGURE THREE is a PARALLEL circuit and voltage is NOT increased it delivers 1.2V no matter how many batteries you add.
      FIGURE FIVE is a series/parallel circuit and AS I SAID WAAAAAAAY EARLIER ALREADY right here…
      With the last of those 3 links. Is what BT would have to use if they wanted to use phone lines to power it.

      Ill repeat learn what ohms law is.

      LMAO, how many more times do we have to explain the difference to you in a circuit and that you can not break the laws of physics.

      NOCLUE is right on another thing i should just give up. Though watching you not understanding the difference between 2 things is always entertaining.

    2. Avatar MikeW says:

      For figure 3, you did read the part about the current, didn’t you. To save looking, I’ll repeat it here:

      The voltage of the illustrated pack remains at 1.2V, but the current handling and runtime are increased fourfold.

      Figure 1 gets 1000mA, while figure 3 gets 4000mA. Oh. You didn’t see that part? Try booking an appointment at Specsavers.

      I’ll repeat (seemingly ad nauseum): I am not looking to increase the voltage by putting the lines in parallel. I have never claimed to.

      By putting lines in parallel, I am looking to increase the available current.

      Let me know when you figure out what what we’re trying to achieve. Problem is, that requires you to read what I write, and then pause while thinking things through. You are so busy LYAO that your brain is being starved of oxygen.

      And this had me PML:
      “Ill repeat…
      “CURRENT is affected by either voltage or resistance. If the voltage is high or the resistance is low, current will be high.”

      You did read the part about where batteries have internal resistance? By putting them in parallel, you are placing the two resistances in parallel – which gives low resistance. As you nicely point out, when resistance is low, current will be high.

      As you just agreed with me, you must be left just arguing with yourself.
      A real Mastercard moment.

    3. Avatar No Clue says:

      OMG its DC its the voltage that matters.

      Figure 3 will deliver the same voltage as a singular battery, all what will happen with figure 3 having a higher amperage per hour is the battery power supply will last longer, or as the description states….

      “The total power is the product of voltage times current, and the four 1.2V/1000mAh cells produce 4.8Wh.”

      Figure 3 does NOT deliver or “get” (whatever you mean by that) 4000mA.

      mAh stands for milliamps per hour.

      The higher that figure the longer a battery will last, its bugger all to do with how much power it supplies the other end to something, or how much power a parallel circuit can deliver that is the volts in a DC circuit.

      mAh is capacity NOTHING MORE.

      If you want to supply more voltage a parallel circuit will not do it. A parallel circuit delivers only the maximum of the highest supply in its chain of power in the case of your diagram 1.2V. <<< As we keep trying to explain to you but it appears you do not understand simple diagrams or what terms like mAh mean.

      If others need "specsavers" you need to get back to school and redo your science GCSE, cos you do not even understand the difference between current and capacity, ill help….

      My god mAh = morrrrrrre pwwwwwwrrrr now does it LMFAO

      Im seriously done with you now, you have made some goofs in your time by not comprehending voltage and capacity is a new level.

      Might of helped if you googled what mAh was first before your bought of rage. It certainly is a Mastercard moment but not for the reasons you thought.

      Ill leave you with one thing… Please never touch anything electrical. Its for your own good.

    4. Avatar MikeW says:

      “OMG its DC its the voltage that matters.”

      It is the power that matters. P=(V*I), so to increase total power, you can raise the voltage or raise the current, or both.

      I am trying to raise current, not voltage. The designers of remote power systems and reverse power systems are doing the same thing.

      In these examples, it is the current that matters.

      “Figure 3 does NOT deliver or “get” (whatever you mean by that) 4000mA.”

      Sorry – “get” is indeed pretty loose terminology. Everywhere else I have said that putting batteries in parallel makes the higher current available.

      What does that “available” mean?

      Simply, it means the higher current is available for the load circuit, if that load circuit needs it (ie is designed to draw that much current).

      The maximum current you can draw from one battery is governed by the internal resistance. If the load circuit (whatever it is) really wants to draw more current than that, it finds it is limited by that internal resistance.

      By putting 4 batteries in parallel, you put the internal resistances in parallel too. Those resistances follow Ohm’s law as normal – so the overall effect is a lower effective resistance in the circuit, such that higher current – up to 4000mA in this case – can be drawn.

      When does this matter?

      Putting batteries in parallel will have negligible effect on the overall current flow if the load circuit has a resistance that is tens, hundreds, or thousands times higher than that of the battery itself. The load circuit is the limiting factor there.

      If, however, the resistance of the load circuit is of the same order as the internal resistance of the battery, or lower, then the current will increase: the battery itself has become the limiting factor.

      Beginners at electronics forget about the effect of the internal resistance, as described here:

      Standard 1.5V torch batteries have a high internal resistance, so the current flow is limited – even if you short circuit the terminals. This type of battery easily becomes the limiting factor.

      A 12V lead-acid car battery has a very low internal resistance, so the current flow can become huge if the terminals are shorted: tools can be melted this way.

      “mAh is capacity NOTHING MORE”

      Agreed. By adding more cells, you increase the capacity. I agree with that too.

      I’m not entirely sure why you bring up capacity, though. It makes no odds to this discussion.

      Look back at the diagram for figure 3. Contained within the diagram itself, you’ll find that it shows 4,000mA. Not mAh. You don’t need to go looking in the text related to an entirely different picture to find it.

      Putting 4 cells in parallel quadruples the current available (important word, that “available”) and quadruples the Ah capacity too. If the original load continued to draw 1,000mA, then it would now be able to run for 4 times as long with the 4 cells, making use of the higher capacity. However, if the circuit design wants to draw the full 4,000mA, then it would not get that extended life.

      Here is another page on putting batteries in series and/or parallel.
      Note the second circuit, where the batteries are placed in parallel (quote) “for greater current capacity (lower internal resistance), or greater amp-hour capacity”:

      Let me repeat what it says in the review:

      Connecting batteries in parallel increases total current capacity by decreasing total resistance, and it also increases overall amp-hour capacity

      “If you want to supply more voltage a parallel circuit will not do it.”

      Read my lips. I do not want more voltage. How can I put it plainer? How many times do I have to repeat that simple statement?

      You keep trying to bring the conversation back to something that is not wanted. You want to bring in terms (like mAh) that, while I fully understand, are irrelevant to the conversation at hand.

      What conclusion do we reach here?

      Simply that you do not understand that putting the power source in parallel increases the current available. Without that simple understanding, you remain unqualified to continue discussion on anything here that depends on that basic knowledge.

      Back at the beginning, the conversation started with looking at tricky things, such as the patent on remote power, and the intricate details of reverse powering.

      However, we seem to have boiled down the problem to one simple thing that you have wrong. Until you correct that failure, there is no point in continuing the conversation.

      If parallel power supplies continues to be a topic too tricky for you, then I can only point you back at the PDF I did for you. There’s only one power supply there: you only need to cope with wires that are in parallel.

    5. Avatar Raindrops says:

      An ampere-hour is not a unit of energy. In a battery system. You have NOT raised the current, you have raised the CAPACITY of the battery or power system. Nothing more.

      It does not matter how many mAh you have if the voltage supplied is only 1.2V.

      Or a simple example……………..

      How you gonna power the node at the pole with your parallel circuit if each node is say 12V and your power system has 1,000,000 mAh, but still can only deliver 1.2V NO MATTER HOW MANY WIRES you run to that node (IT wont MATTER a parallel circuit can NOT increase voltage)???

      Hint you aint gonna be powering it.

      BT as you have been told over and over would have to use SERIES PARALLEL…

      The only time mAh enters the equation is how long the power will last, and as im assuming BT would not be using batteries that becomes partly redundant anyway (unless for a change they want to be efficient and modern).

      VOLTAGE is the power in a DC circuit, Watts is the consumption, and amps-hour, is the capacity (or basically the bigger the number the longer it will last). Its voltage that is lost over long runs of cable not amps-hour.

      If you can not comprehend the basics, then that GCSE link just suggested to you might be a good starting point.

      Im going to let you have the last word on this now, because as No clue points out you do not understand electronics.

      Ah BT employees, especially ones previously sued by former ISP employers for typing other untruths online. Beyond any type of educating.

    6. Avatar No Clue says:

      “Ah BT employees, especially ones previously sued by former ISP employers for typing other untruths online. Beyond any type of educating.”

      LOL oh dear that has set him off back into his regular character for new posts today. Back in to regular MC RAgE mode 😉

    7. Avatar TheFacts says:

      None of this series parallel stuff has anything to do with how this technology would be powered from multiple sources.

      How about DC/DC converters to isolate the individual sources. Plus many properties have 2 pairs, so one could be used for remote powering.

    8. Avatar No Clue says:

      “None of this series parallel stuff has anything to do with how this technology would be powered from multiple sources.”

      Really you know of another type of wiring schematic?

      “How about DC/DC converters to isolate the individual sources. Plus many properties have 2 pairs, so one could be used for remote powering.”

      OH dear… Many homes do not have 2 Pairs, some have a spare pair in the DROP WIRE bundle that comes into their home (cos its 4 cores or 2 pair).

      What is in the drop wire and what is available at the pole are totally different.

      There is no spare pairs left at my pole yet my incoming DROP WIRE cable has 2 pair. Good try though. Quite funny now that you think cos a drop wire in someones home has extra wires in it that equates to extra pairs being available at the pole. If that were the case a pole that supplies 15 homes according to you will have at least 15 spare pairs at the pole.

      I suggest you look at the wire that runs up a telephone pole and the explain what magic trick is used to make 60 separate wires (or thats 2x 15 pairs in case your maths fails you again) total fit into a cable not much wider than a single centimetre.

      Id love one of them to network my house, maybe you can get David Blaine to magic me up a nice supply of them on your magical journey.

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