Ex TPON areas - FTTC/FTTP

Just reading the other thread about multiple PCPs in an ex TPON area.

Are Openreach missing an opportunity for a conversion to GPON FTTP?

Anyone got any idea how much, if any, of the original infrastructure could be adapted for GPON? I'd guess the endpoint hardware is useless but what about the existing fibre runs, fibre tubing and ducts? How much of the TPON infrastructure would have survived copper overlays done a decade ago for ADSL?

Unlikely that the fibre goes anywhere useful. Nga has been built as a new network with a different set of targets, one of which is to ultimately make many local exchanges redundant.
Duct is duct, whether it carries copper or fibre tubing, the main concern is where it goes to/from, does it have space and is it clear. Chances are that there is very little Tpon network that could be usefully re- used

I was surprised that it isn't actually more cost effective to deploy FTTP than 5* FTTC cabs for such a small area.

When I quizzed openreach about it, they didn't really have an answer.

Edited by kingbiscit (Thu 03-Sep-15 13:12:27)

Who in Openreach did you quiz? If it was an engineer then likely they wouldn't know.

The problem with FTTP is that final few yards to the property. With FTTC there is pretty much nothing that needs to be done within the bounds of the house. With FTTP they might have to dig up driveways, run internal fibre cabling, etc, etc. The difficulties of an FTTP install can be significant.

It was at a Connecting Cheshire event, someone running the project. He said they heavily favoured FTTC as people could get it without any additional work e.g. it can just be turned on. FTTC would require an installation at the property.

Personally I think its very short sited, the estate has ducts all the way round it.

My brother moved into a brand new estate that had ducts all around. The estate 18 months after he moved in finally got FTTP. It took another 6 weeks for him to get it because, despite being brand new, the ducts to 5 houses were blocked. I don't know how much resource it took to clear the blockages but it shows that even where there are ducts there is potentially more work to do to get the fibre in. Plus, the it took 2 engineer visits, 1 to run fibre to the outside of the building and then another to run it along the building and into the house. Plus fitting of the ONT inside the house and getting it all set up.

Still quite a bit more worked involved than for FTTC and therefore more costly to BT.

The other thing to consider is that a very small number of ISPs resell the FTTP variant. That means anyone who has FTTP is far more limited in who they can buy services from - from a choice perspective FTTC is better - although that is something of a chicken and egg situation as more FTTP would increase the likelihood of ISPs reselling it.

That will play a factor, but if FTTP was say half the price of FTTP then am sure that would have been used.

The need for visits to do the final fibre drop and splice it into the home should not be under estimated, plus finding yet more blocked ducts due to ground movement/roots adds to the roll-out difficulty.

In effect you spend less on technology, but a lot more on labour and time for FTTP.

I was interested to find out whether TPON leaves anything useful to make FTTP easier than it might otherwise be - sounds like it doesn't. But, by definition, TPON will be on a post 1990 development which like other similar developments will have full ducting to everyone's doorsteps.

Sooner or later Openreach need to bit the bullet an increase the FTTP footprint - these estates would seem to be a good place to start as for the most part it shouldn't have the issues of crossing gardens and direct buried cables. I think it's time maybe they should try a trial area to find out if it is significantly easier than other brownfields. Cost of FTTC cabs and associated power feeds, etc can be offset against it plus the end result is future proof.

Do these TPON nodes have existing power? If not FTTP then perhaps it makes FTTrN/G.Fast straightforward?

Yes TPON cabinets have power to them. As has been mentioned previously the fibre used for TPON might not be going to the same exchange as the FTTC fibre needs to go to. If it's heading in the right direction I can't think of a reason why you couldn't slice into the TPON fibre at the nearest FTTC aggregation node and connect it there. Obviously the other end would need connecting to the new FTTC cab too. Saving on labour.

But there might be something technically different about the fibre used back then. To me fibre is fibre though and it's what you put at each end that makes the difference but like I say I could be wrong.

Icarus

NO, TPON ( Telephony over Passive Optical Network ) cabinets do not have power to them , the operative word is Passive. The cabinets are pillars really for the final splitter. 32 way.

The fibre could be reused easily for a GPON solution or FTTP but thee is little space for the final connection.

The final run to the house should have been sub-duct, it was suggested to make this figure of 8 with the Cu in the big part leaving the fibre to be blown down the small part later. But I don't think all sites used this.

They were usually new estates so were buried under drives and would be difficult ( expenses) to dig up now.

The splice point would have to be rebuilt to take the final splices which could also be expensive, TPON was just a connection to a 30 Connection Cu unit per 'close' usually up to 24 homes.

Much to my regret the cheapest / quickest solution is a new cab on the overlay Cu run. But it really is a shame not to reuse the fibre when it was 20m from your door.

As you may have gathered I had something to do with planning some sites back in the early 1990s, it was a great way to reach a long way from the exchange for voice, some were well outside the normal limits for copper and would have needed a new exchange building. Shame the 'pillars' were not bigger but hindsight is a wonderful thing.

If TPON cabinets were passive, how did they convert the light signals into something that would travel down a copper pair?

PON networks while passive do need power to the lasers at each end of the fibre.

In reply to a post by MrSaffron:

If TPON cabinets were passive, how did they convert the light signals into something that would travel down a copper pair?

PON networks while passive do need power to the lasers at each end of the fibre.

And the old-style phones at the end of the copper need that -50V level to work at, and to be able to signal on/off-hook.

That voltage has to come from somewhere.

Andrew

I wasn't involved in the provision of that bit of the technology, but we never had to provide power at the final splitter ( or the intermediate one) in the way they do with FTTC.

I wonder now if as all the estates we fed would have had street lighting and if it was fed directly off that by the builder. ( It never seemed to be affected by power outages either though, but all the power infratructure for the estate would be new as well). Certainly no batteries or other power infrastructure but must have got 50v from somewhere. ( The pillars are amazingly small.)

Certainly the intermediate spitters needed nothing, jusr split the wavelengths into 30 different fibres.

Same as fttc rollout then aggregation nodes and splitters don't need power either

The reason I thought the TPON cabinets had power to them is that I could swear blind that I've seen a sticker on one to that effect. I'm sure I've also seen a training document to say to stay clear of one part of the TPON cabinet as it has power to it. I could be wrong though.

I don't know what you mean by pillar by the way, I'm talking about those big, wide, grey TPON cabinets.

I've just been googling to find descriptions of a TPON network architecture, and everything (not BT specific) generally seems to put the remote electronics into an ONU that is placed in the home - effectively a variant of FTTP. These descriptions do include a passive splitter - which may be the small pillar, rather than the large cabinet.

However, I've come across a 2005 Analysys report for Ofcom, as part of their study into the "cost of the BT local loop network".

It has this to say about TPON:

In reference to stakeholders.ofcom.org.uk/binaries/consultations/copper/annexes/loo...:

There have been within BT a number of small trial scale deployments (of order 30,000
lines � approximately 0.1% of all BT lines) of TPON systems. Whilst these trials have
undoubtedly shown that such systems are feasible for either a fibre to the DP architecture
(in the past) or a fibre to the premises solution (in a more recent trial), they have not yet
demonstrated economic viability for the current service set. We understand that a new
build of TPON would use a similar duct layout to the existing network (i.e. a �tree�), and
that it would therefore face very similar costs to the existing network for duct and fibres.
Unfortunately for the economic case for TPON however, there is an additional significant
cost, the CPE (Optical Network Unit, ONU), currently costing several hundred pounds per
line: accordingly significant additional service revenues would be needed to make it
attractive compared to the existing architecture. It is therefore not a modern equivalent
asset we will consider further in this study.

That suggests the ONU has been tried in both the premises, and in a DP-like location.

It also has this to say on power backup:

We understand that the BT TPON deployments with fibre to the cabinet have of order 8hrs of battery backup
power.

Use of battery backup suggests mains power is needed in the first place.

Given the numbers of tpon users with adsl when copper overlay was added between cab and exchange the ont in home I think was rare

I've never seen any kind of ONU in a home and I've worked a lot in ex-TPON areas. I'll do some digging and find out exactly how BT did it.

I've found out the info, don't ask for a source because I can't give one but larger business customers could be served by an optical unit inside the building. Small businesses and residential customers were served by an optical unit housed in street cabinets. Each cabinet connects up to 32 lines or 128 lines depending on the cabinet used.

I can confirm that the grey TPON street cabinets 100% DO have 240v power to them. I've found the warning that I was talking about before.

Edited by deleted (Sat 05-Sep-15 14:16:18)

That makes perfect sense as something has to power the optical/electrical interface, and I don't think a 50V supply from the exchange would do it (due to resistive losses), nor do I think that "reverse power" from the premises be at all likely (I've never heard of such a thing).

What I imagine might be possible is that a number of the TPON grey boxes are supplied via low voltage supplies from a nearby one. That's certainly what VM do with their green boxes.

As to whether the supply to the TPON boxes is up to the job of supplying an FTTC cabinet, I've no idea. I suspect TPON used relatively low power.

Thanks for that.

So there may be of the order of 1,000 TPON cabinets out there, with ready access to power, and access to the copper line plant. It seems they make a natural location to place an FTTC cabinet now, even if a bit small. The latter might be a negative point in viability, but no charge for a power supply probably offsets that. Plus those sites are probably well suited to g.fast later.

Why do you say 1,000? Believe it is more like 50 to 100

Some TPON areas now have native FTTP

In any ex-TPON areas that I can think of the TPON cabinets have been left there and FTTC cabinets have gone in as usual. The network was converted to all copper years ago anyway during the ADSL roll out in my area. All the fibre cabinets have fresh fibre to them, the FTTC cabinets are connected to the same exchange as the TPON was as its a large exchange. Seems a waste I agree.

Edited by deleted (Mon 07-Sep-15 11:35:47)

In reply to a post by MrSaffron:

Why do you say 1,000? Believe it is more like 50 to 100

The report figured 30,000 lines, and the cabinets are reported to be capable of either 32 lines, or 128.

If all lines were on the 32-line cabs, that is 1,000. If they were all on 128-line cabs, that'd be 250.

I've seen something (that I now can't find) that gave a hint that the 32-line cab might be more popular, swaying the average higher. But no evidence beyond that.

Some TPON areas now have native FTTP

That'd affect things...

The literature I read made it sound like the 128 line cab came out later than the 32 line one. So it may be in areas that were built earlier on that its pretty much all 32 line. But certainly in my area all TPON cabs are 128 line models.

Also some TPON was totally overlaid as part of the ADSL roll-outs, which may explain the lower number of cabinets now

Andrew

Although OFCOM were quoting 30k line in 2006 these were workers, the capacity was far higher than that and the total was already declining by then.
In the patch I worked on we only used 32 capacity cabs, ( approx 24 houses to alow for 2nd lines). We must have installed 350-400 in total, more likely to be 1000-1200 nationally. I can think of one area alone where there were more than 50 They were prefect at the time for large new estates where a new exchange would be the alternative.

In reply to a post by kitcat:

They were prefect at the time for large new estates where a new exchange would be the alternative.

Isn't it ironic that they effectively presaged the design of the FTTC network we know today.

Installation of a cabinet-based ADSL would have been so much better way to make them broadband-capable, rather than putting copper in. I guess the ideas behind GEA and VULA weren't around at that time...

The "24 houses on a 32-capable cab" is what I'd have expected too, dimensioning-wise.

In reply to a post by WWWombat:

In reply to a post by kitcat:

They were prefect at the time for large new estates where a new exchange would be the alternative.

Isn't it ironic that they effectively presaged the design of the FTTC network we know today.

Installation of a cabinet-based ADSL would have been so much better way to make them broadband-capable, rather than putting copper in. I guess the ideas behind GEA and VULA weren't around at that time...

The "24 houses on a 32-capable cab" is what I'd have expected too, dimensioning-wise.

Interestingly they did also have ADSL cabinets in parts of Scotland. If I'm not mistaken they were in TPON areas as a way of delivering broadband.