Kitz Forum
Broadband Related => Broadband Technology => Topic started by: adslmax on May 11, 2019, 12:40:31 PM
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I just saw MrSaffron posted headline about this VDSL2 upcoming found here: https://www.thinkbroadband.com/news/8403-fifteen-more-exchanges-with-g-fast-ultrafast-broadband-are-now-live
"The interesting part will be if VDSL2 is turned off in different areas whether the spectrum used can be recovered and give G.fast a speed and range boost."
But question is .... What IF the customers want to remain staying on VDSL2 (FTTC) because of cheaper cost than expensive G.fast products?
[Moderator: Subject line adjusted.]
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First of all, I think VDSL2 is unlikely to be a target for a while, probably until full fibre. Openreach will be more focused on removing E-side copper, thus getting rid of POTS and ADSLx, before this.
But there are issues with their current implementation of G.fast that makes getting rid of VDSL2 and moving customers G.fast impossible in most areas:
- Vectoring is intense, so current I believe current port capacity is 48 (96 underway) - compare this to max capacity of 288/344 of the higher capacity VDSL2 cabinets
- They bolted it to the cabinet, so where can they put another pod? (Plus there's the question of vectoring across hardware)
- Current power and fibre is supplied from the existing VDSL2 cabinet - there would need to be new sources
There are others issues I haven't touched on, regarding performance over distance, costs to ISPs to supply new hardware, etc.
However, in the scenario where this did actually happen, ignoring all issues relating to it, I imagine there would be an equivalent package of an equivalent cost to aid progress to move end users over.
My conclusion is that it won't happen and it can't happen under the current amendment (they would really need DP G.fast for it due to capacity). But if it did, then I think there would possibly be a package equivalent to the top tier VDSL2 one (80/20). Even if customers did not want to move, they would have no choice.
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If there was no VDSL then G.Fast could use the frequencies that VDSL uses and thus distance could be increased, I wonder if it would get similar speeds as VDSL at the longer distances if that was the case?
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The logical progression to that train of thought would be FTTDP (Fibre To The Distribution Point) for those EUs where FTTP would prove to be too difficult or impossible to provide.
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I've wondered the same for a while. Without access to the specifications it is a bit difficult to judge (I wanted to look at the ITU documents but I cannot access the website). At least in the UK for G.fast, there's STIN 520 (https://www.btplc.com/SINet/sins/pdf/STIN520v2p0.pdf) which documents the G.fast Pilot, but I don't know if this has been supersceded. Likewise for FTTC, there's SIN 498 (https://www.btplc.com/SINet/sins/pdf/498v7p5.pdf).
No question, G.fast utilising the whole 2-106 MHz spectrum could operate faster further away than with the current state of G.fast with co-existence with VDSL2. Though I would presume VDSL 17a would be able to operate faster than G.fast at the longer distances due to the transmit power being 14.5 dBm (versus 8 dBm with G.fast) alone, but we would probably be talking somewhere nearer to 800-1000m before VDSL2 would be faster. Vectoring can be ignored since the impact it has towards the extremes tends to be very little.
Bear in mind, I am just making a presumption. I have certainly not gone too deep into this. I don't understand what impact a different Divison Duplexing will have, I haven't really looked into the effects on upstream, I have not understood the impact of receiver sensitivity, etc.
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There is the NICC (https://niccstandards.org.uk/) ND1520 document all about options for G.fast using VDSL2 frequencies, and the latest ND1602 Access Network Frequency Plan document lists two scenarios in which G.fast is permitted to start below 18.3MHz. If I've understood the acronyms in ND1602 correctly, the first scenario depends on the distance between the G.fast pod/box and the cabinet, which would be practically zero for a G.fast pod on the side of a cabinet, and so not really applicable to G.fast from the cabinet. The second scenario is a rather unspecific "documented commercial agreement for a given SDF and associated G-SDFs, and as such is subject to consensus between DSLAM operator(s) and relevant CPs".
It's spectrum refarming (adjusting or overlapping the frequencies), rather than turning off VDSL2 completely.
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Hi
At the end of the day the physical line and speeds supported is dependant on physics and attenuation of frequencies.
So assuming all technologies used the same frequencies they would at a certain distance end up all being a similar speed, and wouldn't go much further and would not be faster than a lesser technology.
VDSL is only faster than ADSL because it uses more and higher frequencies, which is why it had to be moved nearer to homes, otherwise there is next to no speed increase. We already know at a certain line length VDSL ends up performing very similar to ADSL at the same distance and has little advantage in long reaches.
G.Fast is faster again because it uses even higher frequencies, but due to various accounting decisions BT decided not to shorten the distance as they did with VDSL to save costs, therefore it only benefits those on lines that are very short. If a line only gets say 60MB/sec on VDSL so already dropping high frequencies due to distance, it will not get that much more on G.Fast, there is nothing magical about G.Fast that suddenly means higher frequencies arrive at the other end that didn't before on VDSL. At some distance assuming G.Fast can use all the same VDSL frequencies and powers, G.Fast will have no speed advantage.
Obviously this ignores technology improvements between the various flavours of xDSL that try to wring a bit more out of POTs, and G.Fast has vectoring which was never enabled on VDSL. However at long line lengths these extra tweaks stop providing much advantage anyway.
G.Fast is trying to polish a turd that was already polished by VDSL, and G.Fast is a desperate attempt at trying to reuse POTs and avoid the inevitable of installing a new network fit for the 21st century. Thankfully BT have realised this now and Fibre First is here.
Regards
Phil
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Thankfully BT have realised this now and Fibre First is here.
Regards
Phil
Sound like the customer who already got G.fast pod with live will not gettting fibre first (FTTP) or it will happen?
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Sound like the customer who already got G.fast pod with live will not gettting fibre first (FTTP) or it will happen?
Not necessarily so, FTTP is in some cases is being built where G.Fast is already available, remember potential G.Fast customers on a cabinet may be a low percentage of the overall number of customers.
The plan is that everyone will have an FTTP connection with copper cable being retired completely, although we are a number of years away from that, but eventually we will all have fibre.
Regards
Phil
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The plan is that everyone will have an FTTP connection with copper cable being retired completely, although we are a number of years away from that, but eventually we will all have fibre.
Regards
Phil
;D ;D Good I shall wait for this FTTP, not bothered with g.fast. Staying with FTTC until FTTP come along.
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;D ;D Good I shall wait for this FTTP, not bothered with g.fast. Staying with FTTC until FTTP come along.
It could be a decade or longer though - so it depends how important/necessary higher speeds are for you
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At some distance assuming G.Fast can use all the same VDSL frequencies and powers, G.Fast will have no speed advantage.
But G.fast uses Time-Division Duplexing, so it can use the whole frequency range for upstream and the whole frequency range for downstream.
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Hi
Time division doesn't increase the total data rate, you just are able to split the ratio between upload/download speeds more easily than VDSL. So if at a long distance you are only getting say 9 down and 1 up on G.Fast, the ISP could choose to swap the ratios to 5 down and 5 up, so yes you may benefit from G.Fast in that respect, but overall data-rate is the same, so no massive differences.
The over-riding limitation on telephone wires is the physical medium of the wire itself, and there is nothing that can overcome that. Despite G.Fast being a new technology, VDSL is also capable of similar speeds over the same shorter distances if allowed to use the same frequencies as G.Fast.
Regards
Phil
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I thought the amount of G.fast ports per pod was very low compared to the VDSL2 cabinet?
There might not be enough ports to transfer everyone over to G.fast... and what happens to the people who was in range for VDSL2 but now out of range for G.fast? They got to go back to ADSL speeds?
I think the more likely change would be to the VDSL2 profile someone mentioned on the forum, 35b (?) as it extends VDSL2 range and would give us all better speeds.
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The plan is that everyone will have an FTTP connection with copper cable being retired completely, although we are a number of years away from that, but eventually we will all have fibre.
The cynic in me says that they'll find reasons not to provide fibre to properties currently on long copper paths.
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Hi
The cynic in me says that they'll find reasons not to provide fibre to properties currently on long copper paths.
They'd be shooting themselves in the foot if they didn't provide fibre as the long term plan is to retire copper completely, they don't want a mixture to maintain indefinitely, so it's in their interest to update everyone to FTTP, although it might be some time away before everyone has fibre, it is happening.
Regards
Phil
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Most of the FTTP overbuild of G.fast is for those who cannot reach >100Mb via G.fast.
If you're far enough away from the pod that you can't hit ultrafast speeds and are in a Fibre First area you might be on Openreach's list.
If you are in a Fibre First area and can hit >100Mb comfortably you're likely not going to be so high on the list. If you're in an area that isn't Fibre First and you can hit >100Mb comfortably you're likely nowhere near the top of the list.
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I would assume the effect of TDD depends in part on the difference in efficiencies between the two TDD vs non-TDD in respect of how the turn-around time in the former and its effect in the Fourier transform compares with the waste of the frequency band gap.
This problem has already been seen and attacked. With the 4.3125kHz inter-symbol gap.
Being able to vary the TDD duty cycle seems like a really big deal to me though. Before TDD there was continuous waste of time on the unused tones whenever the traffic ratio was exactly suitable.
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... They'd be shooting themselves in the foot if they didn't provide fibre as the long term plan is to retire copper completely, ...
That's why I said "find a way" in particular I think they'll find a way to justify discontinuing copper services without providing fibre as a replacement. I don't know how many remote properties there are, but as an example our house is on the end of 5300m of copper, around 900m from the DP. I would love fibre to be provided, but I wouldn't put money on it ever happening.
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But if your line is all overhead then it will be relativity cheap to do, where our estate is all direct in the ground, so it all needs digging up.
Thanks to PhilipD for the great information.
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They wouldnt/couldnt turn off adsl to boost vdsl so why would they do this?
Turning off ADSL would gain them so much more so has a far bigger business case. So no they wont do this.
I think g.fast will just die a short death within 5 years from the first deployment, it will be a failed project. The takeup figures published are completely of no surprise to me.
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I think the more likely change would be to the VDSL2 profile someone mentioned on the forum, 35b (?) as it extends VDSL2 range and would give us all better speeds.
Having VDSL2 use higher frequencies, up to 35MHz for profile 35b, is not really going to increase its range. It's not going to happen.
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But if your line is all overhead ...
All underground unfortunately from that point of view.