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Author Topic: Fibre Crosstalk and Line speed estimate  (Read 605 times)

tomtom

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Fibre Crosstalk and Line speed estimate
« on: February 05, 2018, 04:35:58 PM »

Hi, currently I’m on adsl2+ and get a sync speed of 19mbit. On the open reach line estimator it claimed I could get 15-20mbit which is quite close.

I'm now looking to upgrade to fibre and the line estimate is 19 - 27 mbit down and 1.2 - 2.7 mbit up on a vdsl range A line.

Its a rural area and my phone line is 450m from road (dp pole?) and goes through a field. The same cable feeds my neighbour who is 40m further. With his not so great internal wiring he was getting a speed test of 22mbit and 2.1mbit upload.

What speed could i get? How would 450m crosstalk effect line speed? I know on adsl2+ the line is very stable.

I had a look at the cabinet details and its an ECI approx 1150 - 1220m away

Thanks
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re0

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Re: Fibre Crosstalk and Line speed estimate
« Reply #1 on: February 05, 2018, 07:09:07 PM »

Hi tomtom,

There's no real way for you to accurately predict what you will actually receive until you go live, hence why they are estimates. ADSL speeds don’t give clear insight to how FTTC (VDSL) will perform on the same line since FTTC utilises higher frequencies and it is only the D-side and dropwire which are important.

Range A assumes a relatively clean line without bridge taps or wiring issues. This is the best case scenario speed and the DSL checker is usually pretty accurate, and over time the system does change its estimates based on conditions as it collects data – for one line here the downstream Range A has gone from 80-79 to 80-71 (High/Low) since the cabinet went live two years ago, but it still synchronises at the top end of the scale as it is free from bridge taps and apparent wiring issues.

I would say the 450m of crosstalk would already be taken into consideration with the estimate. The only way to find out how much impact would be to politely ask all of your neighbours using the broadband spectrum to switch off all their broadband hardware when you have FTTC ;).

You are most likely to receive approximately the same speed as neighbours within the same geographical area and those on the same pole as yourself, give or take a few megabits depending on quite a few factors. However, bear in mind that the following will have an impact on what speed you can receive on FTTC (I will try and cover as much as I can):

- Distance
Distance leads to attenuation of the line. The shorter the better, but the attenuation is also amplified by the material and gauge alongside the distance.

- The material of the pair:
It can be either aluminium, copper or even a mix of both depending on when it was originally laid, and when parts of it have been replaced. Copper is a better conductor, and will attenuate less over distance. Aluminium is no longer implemented in networks post-broadband.

- The gauge of the pair:
The gauge of the pair has a bearing on attenuation, and 26 AWG (0.4mm) is the standard for Openreach from what I have read which apparently attenuates at 13.81 dB/km @300kHz. 24 AWG (0.51mm) is used in some cases, which fares better and attenuates less at 11.90 dB/km @300kHz. In some areas, they may use the thicker gauge to reduce attenuation in rural areas with long lines. But I have heard that in some areas that had lines laid pre-broadband may even use 26 AWG aluminium which can attenuate at a much higher rate and be more susceptible to interference.

- The quality of the pair:
If the pair has had sections repaired or replaced in the past, it may be subject to high resistance at joints. Furthermore, if there has been water ingress in any part of the copper network then there may be corrosion which can also lead to a drop in sync speed and more errors. Though, in this case, it would be classified as a fault if it is impacting the service.

- Filtering and internal wiring:
Since all new FTTC installs are self-install, unless otherwise requested or if the install is for a new physical line install, there will be no engineer so you will need to ensure your internal wiring is suitable and you are responsible for it. You can use the same filters you use with ADSL, but you may want to have a few handy just in case your current one is or goes faulty, or if the speeds are below what are expected. As for wiring, http://www.kitz.co.uk/adsl/socket.htm may be a good read.

- Modem (chipset):
Choice of modem will have, in some cases, a large impact on what you can receive. Some modem/router combos provided by ISPs may come with a Lantiq broadband chipsets (like the BT Home Hub 5A and Plusnet Hub One). These chipsets may work well on short lines, lines less susceptible to interference and lines which are less subject to interferences. However, in my experience, Broadcom chipsets have always worked best when previously on a long line with ADSL2+ provisioned and even on a short FTTC line compared to Lantiq, allowing for a higher sync and less reported errors on the line. I do not think things have changed since then, and on a budget I would highly recommend a Billion 8800NL myself, and I imagine people here would say the 8800NL R2 is just as good (and it is slightly newer) as both come with a Broadcom chip.

- FTTC DLM (Dynamic Line Management) setting provisioned by ISP
This may prove to be a good read http://www.kitz.co.uk/adsl/DLM.htm. Your ISP will provision you with a certain stability setting, and this sets out your error and resync tolerances before the DLM makes changes to “stabilise” your line. Since you are at the mercy of the DLM, even if things appear stable, it is ultimately the thresholds that will decide how stable the line is. Even if you experience only a short burst of errors, it may contribute to the threshold being breached if it is persistent, leading to the DLM taking action in an attempt to reduce errors (which in most cases will have a negative impact on sync speed).

All in all, the estimate of 19-27 Mbps on the downstream and 1.2-2.7 Mbps on the upstream seems reasonable based on your distance. However, I would not get your hopes up for it being that much faster than ADSL2+ on the downstream, but you may notice a decent uplift on the upstream.

re0
« Last Edit: February 05, 2018, 07:23:22 PM by re0 »
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Black Sheep

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Re: Fibre Crosstalk and Line speed estimate
« Reply #2 on: February 05, 2018, 07:49:19 PM »

Very impressive write-up, re0 ...... a good layman's guide.

Just my two-penneth for clarification purposes, 0.5mm is the 'norm' for D-side cables (The cable from the Cabinet to the customer) ..... 0.4mm was mainly utilised on the E-side cables, (ie: from the Telephone Exchange to the Cabinet).

The only caveat I will apply is, I can only speak in regard to Manchester, and Lancs and Cumbria patches.  :)
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re0

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Re: Fibre Crosstalk and Line speed estimate
« Reply #3 on: February 05, 2018, 08:22:19 PM »

Oops, I should have clarfied what D-side and E-side means. :)

At least you've mentioned it now so it's there - E (Exchange) and D (Distribution).

I probably missed a couple of other things, so someone else will probably fill in the blanks if necessary.

I am pretty sure 0.4mm aluminium is in use around these parts where some infrastructure pre-dates the days of broadband connectivity. But I cannot recall if the last engineer I spoke to confirmed the gauging or not, so it could be thicker.

I should put a disclaimer to state that I am not an engineer and I am not associated with Openreach in any way, so there may some inaccuracies ;)
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renluop

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Re: Fibre Crosstalk and Line speed estimate
« Reply #4 on: February 05, 2018, 11:01:53 PM »

Between roughly what dates was aluminium used? Was it used both overhead and underground?
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tomtom

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Re: Fibre Crosstalk and Line speed estimate
« Reply #5 on: February 06, 2018, 02:03:36 PM »

Hey, thanks for the excellent reply re0 :)

I've just ordered plusnet fibre, seems good deal currently £22.50 / month with line rental saver and £70 cashback

Fingers crossed I will get decent speed bump
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re0

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Re: Fibre Crosstalk and Line speed estimate
« Reply #6 on: February 06, 2018, 04:08:33 PM »

Between roughly what dates was aluminium used? Was it used both overhead and underground?

Is this a test? ;) I can't answer that question since I honestly don't know. :-[ All I know is that aluminium was used around the 70s when copper prices were high, and it did not matter as long as the telephone service worked since that is all GPO had to worry about.

Hey, thanks for the excellent reply re0 :)

I've just ordered plusnet fibre, seems good deal currently £22.50 / month with line rental saver and £70 cashback

Fingers crossed I will get decent speed bump

Keep us posted with your installation! :fingers: for the speed being somewhat faster on both the downstream and upstream.

It will be at least 10 working days before installation from the moment they receive and review your order.

Perhaps invest that cashback (when you receive it) into a new router with a Broadcom chipset? ;D I would not personally use the Plusnet Hub One (even if I opted to receive it, but would certainly keep it as a spare).
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Black Sheep

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Re: Fibre Crosstalk and Line speed estimate
« Reply #7 on: February 06, 2018, 05:59:45 PM »

Between roughly what dates was aluminium used? Was it used both overhead and underground?

Same here, I too can't give definitive dates ........ but I can pass on what our trainers have said a few times over the years, and that is they moved to aluminium as the cable-of-choice, post-WW2 .... not sure how 'post' but it was definitely related to the hike in Cu cables.   :) :)

Maybe 4candles has more info, a long shot I know. 
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burakkucat

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Re: Fibre Crosstalk and Line speed estimate
« Reply #8 on: February 06, 2018, 06:39:27 PM »

I quote from an article titled "A Personal View of the Local Loop Over 30 Years", by J.W.Young (BT Worldwide Networks South), British Telecommunications Engineering, Vol. 10, Part 1, April 1991, p4.

The synopsis --

"This article reviews the history of the local loop over the past 30 years and gives some observations with the benefit of hindsight."

The third paragraph, under the "Works Practices" heading of the "LOCAL LOOP HISTORY" section, reads as follows --

"Development continued in the early-1970s, but at a slower pace. A major change in 1972 was the introduction of aluminium conductor cables, as a replacement for copper. This change was driven by increases in copper prices and forecasts of continuing higher-than-normal copper prices. In the event, these predictions were unfounded and copper prices restored to traditional levels. Unfortunately, aluminium conductors had severe problems and even a change to an aluminium alloy failed to avoid a serious maintenance legacy. So copper technology again became the standard practice."
« Last Edit: February 06, 2018, 08:17:04 PM by burakkucat »
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re0

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Re: Fibre Crosstalk and Line speed estimate
« Reply #9 on: February 06, 2018, 07:17:55 PM »

Nice find. Hindsight is wonderful, especially in reference to the use of aluminium in telecommunications. May its legacy live on the form of higher attenuation, lower sync speeds and higher fault incidence for those unfortunate enough to have it ... :P ... including me :'( (but hopefully only on the E-side :fingers:).
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burakkucat

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Re: Fibre Crosstalk and Line speed estimate
« Reply #10 on: February 06, 2018, 08:20:09 PM »

... including me :'( (but hopefully only on the E-side :fingers:).

I believe it was (is) more prevalent in the D-side than the E-side.  :-X  :(
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