User comments on ISPs
  >> BT Broadband


Register (or login) on our website and you will not see this ad.


Pages in this thread: 1 | 2 | 3 | 4 | >> (show all)   Print Thread
Standard User allofus
(newbie) Sun 02-Nov-14 10:08:55
Print Post

BT Infinity and line length


[link to this post]
 
We live in a village that is getting BT Infinity as part of BDUK. The BT Openreach engineer said that BT Infinity which uses VDSL2 performance drops off dramatically (like a cliff were his words) when the copper line length exceeds around 300Mts. Any Aluminium in the line also degrades speed quickly. Also, as more Infinity customer are in your cabinet / line then cross talk increases and speed drops. BT are now getting requests to go back to ADSL2 after an Infinity 'upgrade'.

I found a chart from apparently Ofcom which shows how VDSL2, VDSL and the ADSLx compare by length of line - http://nbnmyths.wordpress.com/why-not-fttn/.

My question is why does BT persist with VDSL2 when for longer real world line lengths VDSL gives better performance?
Standard User BatBoy
(legend) Sun 02-Nov-14 10:30:51
Print Post

Re: BT Infinity and line length


[re: allofus] [link to this post]
 
At 300m you can get 50Mbps down and 18Mbps up. Is that not enough?


____________________________________________________________________________All_Quiet_on_the_Western_Front__________________
Standard User MHC
(sensei) Sun 02-Nov-14 10:44:16
Print Post

Re: BT Infinity and line length


[re: allofus] [link to this post]
 
No idea where that graph came from ... but it not very accurate and does not reflect actual experiences.

My line length from the cabinet, for example, is 600metres using SatNav or 460 metres following the track on Google Earth. Currently I am getting a sync of around 72 Mbps, max achievable of 74 and throughputs at about 70.

According to that graph I should be seeing about 20-25 ...


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit


Register (or login) on our website and you will not see this ad.

Standard User tdw42
(newbie) Sun 02-Nov-14 11:24:14
Print Post

Re: BT Infinity and line length


[re: allofus] [link to this post]
 
The graph on this page is more representative http://www.increasebroadbandspeed.co.uk/2013/chart-b... but still errs on the conservative side.

When Openreach deploy vectoring technology it should reduce crosstalk and improve performance on cabinets with many subscribers.

Don't overlook the fact that the connection from the cabinet to the premises is only the last leg of a long journey for data packets - the (shared) connections from the cabinet to exchange, exchange to ISP, ISP to the internet are overcommitted and may become congested; the ISP may control the flow of some categories of traffic in an attempt to reduce congestion, so in many cases 'the internet going slowly' is not due to the final part of the journey.

As to switching back, it depends on expectations and what you are prepared to pay - if you only have 1-2Mb ADSL but can get at least an order of magnitude more with FTTC you may well be happy to pay more for the service so you can stream films/catchup TV, but if you have at least 6Mb ADSL and would only get 20-30Mb with FTTC you may not be...
Administrator MrSaffron
(staff) Sun 02-Nov-14 11:35:55
Print Post

Re: BT Infinity and line length


[re: tdw42] [link to this post]
 
And then of course there is http://www.thinkbroadband.com/guide/fibre-broadband.... it may look pessimistic but we took account of crosstalk impact from day 1

There is also http://maps.thinkbroadband.com/#!lat=54.628258777628... where we have calculated a speed for every postcode (outside NI) on the assumption every cabinet gets a FTTC service

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User TheEulerID
(learned) Sun 02-Nov-14 11:49:47
Print Post

Re: BT Infinity and line length


[re: allofus] [link to this post]
 
VDSL is used because it's about 10-15% of the cost of putting in FTTP.

There are other technologies on the way to push fibre further into the network but basically the closer it gets to the premises, the more expensive things become.

As for "dropping off a cliff", I get 57Mbps at 700 metres (which is just about bang on what the prediction would be). You get decent speeds up to about 1km, but by 1.5km it's not up to much.
Standard User TheEulerID
(learned) Sun 02-Nov-14 11:57:20
Print Post

Re: BT Infinity and line length


[re: MrSaffron] [link to this post]
 
I'm on a 700m line and sync at 57mbps (and the cabinet has been enabled for a year or so). SO that downstream speed does seem pessimistic to me. However, upstream is about what I get.

However, I'm not wholly certain you can go with one prediction. Apart from local line conditions, I seem to recall that the SNFP for sun-loop unbundling had different power masking requirements depending on how far the cabinet is from the exchange. I don't know for sure if that affects the VDSL frequency plan used in the UK or if it plays any part in BT's FTTC product.
Standard User MHC
(sensei) Sun 02-Nov-14 12:33:15
Print Post

Re: BT Infinity and line length


[re: MrSaffron] [link to this post]
 
Your figures are extremely pessimistic:

Take three ways to measure my distance from the cabinet and your forecast:

Direct straight line, cabinets to pole to house: 380m estimate: 43/16
Measured on Google Earth: 460m estimate: 40/15
By satnav and walking: 600m estimate 35/14

Allow for distortions on GE and innacuracies of the phone based satnav and I am probably around or just under 500m away.

I am now getting 68 to 70 down and around 18 up. Down stream sync is over 70 and max attainable rates are shown as 73/23 In the past I had also seen a slow drop off due to cross talk.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User BatBoy
(legend) Sun 02-Nov-14 12:46:43
Print Post

Re: BT Infinity and line length


[re: MHC] [link to this post]
 
What's your attenuation?


____________________________________________________________________________All_Quiet_on_the_Western_Front__________________
Standard User RobertoS
(elder) Sun 02-Nov-14 12:51:06
Print Post

Re: BT Infinity and line length


[re: TheEulerID] [link to this post]
 
In reply to a post by TheEulerID:
VDSL is used because it's about 10-15% of the cost of putting in FTTP.
Errm - that might confuse the OP wink.
In reply to a post by allofus:
My question is why does BT persist with VDSL2 when for longer real world line lengths VDSL gives better performance?


My broadband basic info/help site - www.robertos.me.uk | Domains,site and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 56.4/14.5Mbps @ 600m. - IPv4BQM IPv6BQM

"Angels can fly because they can take themselves lightly." - G K Chesterton.
Standard User RobertoS
(elder) Sun 02-Nov-14 12:51:38
Print Post

Re: BT Infinity and line length


[re: allofus] [link to this post]
 
See the figures in my sig. As you were told however, aluminium between you and the cab could screw things a bit.

My broadband basic info/help site - www.robertos.me.uk | Domains,site and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 56.4/14.5Mbps @ 600m. - IPv4BQM IPv6BQM

"Angels can fly because they can take themselves lightly." - G K Chesterton.

Edited by RobertoS (Sun 02-Nov-14 12:52:24)

Standard User MHC
(sensei) Sun 02-Nov-14 13:00:01
Print Post

Re: BT Infinity and line length


[re: allofus] [link to this post]
 
In reply to a post by allofus:
My question is why does BT persist with VDSL2 when for longer real world line lengths VDSL gives better performance?



Does it?

From around 1200m the performance, according to that graph, is very much the same.


It is also wrong putting ADSL and VDSL directly together as there is a additional unknown line length before a cabinet. So for example a 400m VDSL line might replace a 4km ADSL


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User MHC
(sensei) Sun 02-Nov-14 13:01:37
Print Post

Re: BT Infinity and line length


[re: BatBoy] [link to this post]
 
No idea at present. Currently running an ECI modem so no stats. The ECI gives a slightly higher speed than the Huawei - with a Huawei cabinet.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User Fastman2
(member) Sun 02-Nov-14 13:47:40
Print Post

Re: BT Infinity and line length


[re: allofus] [link to this post]
 
For the avoidance of douby you are getting Ethernet GEA which is delivered by Openreach -which allows 60+ service providers to offer FTTC service one Which BT Retail offer a product called ifninty (infinity can only be sold at >15 meg) other service provers such as talk talk. plusnet sky, ident - etc etc may offer a different product at different price points
Standard User MHC
(sensei) Sun 02-Nov-14 13:57:24
Print Post

Re: BT Infinity and line length


[re: BatBoy] [link to this post]
 
And here is the test at 500m or so:

http://www.thinkbroadband.com/speedtest/button/14149...

Don't worry about the Upstream - it is being restricted to 10Mb by the router!


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User BatBoy
(legend) Sun 02-Nov-14 13:58:49
Print Post

Re: BT Infinity and line length


[re: Fastman2] [link to this post]
 
In reply to a post by Fastman2:
For the avoidance of douby
Why do all your posts start with this?


____________________________________________________________________________All_Quiet_on_the_Western_Front__________________
Standard User BatBoy
(legend) Sun 02-Nov-14 14:04:06
Print Post

Re: BT Infinity and line length


[re: MHC] [link to this post]
 
The attenuation would be really interesting. Haven't you got a HH5?


____________________________________________________________________________All_Quiet_on_the_Western_Front__________________
Administrator MrSaffron
(staff) Sun 02-Nov-14 14:08:51
Print Post

Re: BT Infinity and line length


[re: MHC] [link to this post]
 
And while they are pessimistic I get ripped apart from I give estimates saying they are too high at other times.

The fact I get slated for being both above and below suggests we are in the right sort of area.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Administrator MrSaffron
(staff) Sun 02-Nov-14 14:11:57
Print Post

Re: BT Infinity and line length


[re: TheEulerID] [link to this post]
 
Three different power masks are running, depending on the distance of the cabinet from the exchange, with the masking done to try and ensure existing ADSL and ADSL2+ services do no see any reduction in speed from VDSL2 cross talk.

So very much part of what Openreach deploy.

Best thing is for people to get speed tests onto our maps i.e. run with postcode supplied and we can over time compare this with our estimates and use that to refine things.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User MHC
(sensei) Sun 02-Nov-14 14:19:11
Print Post

Re: BT Infinity and line length


[re: BatBoy] [link to this post]
 
No!

And at present I have been asked to keep the ECI/2701 combination running. And I need the VOIP interface.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User mikejp
(regular) Sun 02-Nov-14 15:11:03
Print Post

Re: BT Infinity and line length


[re: allofus] [link to this post]
 
allofus -
"The BT Openreach engineer said that BT Infinity which uses VDSL2 performance drops off dramatically (like a cliff were his words) when the copper line length exceeds around 300Mts."
- either you misheard him or he is talking out of his comglomeration point... Infinity uses VDSL which does not 'drop off a cliff' at 300m like what VDSL2 does. It fades gently to oblivion around 1500m
Standard User MHC
(sensei) Sun 02-Nov-14 15:43:36
Print Post

Re: BT Infinity and line length


[re: mikejp] [link to this post]
 
In reply to a post by mikejp:
allofus -
"The BT Openreach engineer said that BT Infinity which uses VDSL2 performance drops off dramatically (like a cliff were his words) when the copper line length exceeds around 300Mts."
- either you misheard him or he is talking out of his comglomeration point... Infinity uses VDSL which does not 'drop off a cliff' at 300m like what VDSL2 does. It fades gently to oblivion around 1500m



No, Infinity uses VDSL2


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User mikejp
(regular) Sun 02-Nov-14 16:14:45
Print Post

Re: BT Infinity and line length


[re: MHC] [link to this post]
 
Ok - my mistake, but he was still wrong about 300m was he not?
Standard User Fastman2
(member) Sun 02-Nov-14 16:51:07
Print Post

Re: BT Infinity and line length


[re: BatBoy] [link to this post]
 
they dont all only the ones that are factual statements-- trying to de muddy the mis information
Standard User Fastman2
(member) Sun 02-Nov-14 16:54:01
Print Post

Re: BT Infinity and line length


[re: mikejp] [link to this post]
 
he shoudl get some ulpft up to around 1.4 - 1.5km depending on his line quality of line and local conditions and distance from DP to premise

Edited by Fastman2 (Sun 02-Nov-14 16:54:38)

Standard User BatBoy
(legend) Sun 02-Nov-14 16:55:22
Print Post

Re: BT Infinity and line length


[re: Fastman2] [link to this post]
 
Perhaps you didn't notice this is the BT Broadband forum.


____________________________________________________________________________All_Quiet_on_the_Western_Front__________________

Edited by BatBoy (Sun 02-Nov-14 16:56:20)

Standard User TheEulerID
(learned) Sun 02-Nov-14 16:59:41
Print Post

Re: BT Infinity and line length


[re: MrSaffron] [link to this post]
 
Post codes can be a bit coarse. In my case the centre of the postcode area (according to Google) is 250 metres closer to the cabinet. In addition, there's the distortion caused by those on capped packages, either by capped sync speed or by throughput (as happens on some offerings). Unless compensated for, they will skew the results.
Standard User TheEulerID
(learned) Sun 02-Nov-14 17:03:13
Print Post

Re: BT Infinity and line length


[re: RobertoS] [link to this post]
 
Oops. I didn't read the question properly. In that case, the right answer is that using VDSL2 doesn't decrease reach, it just increases the speed for shorter reach lines (a little bit simplified of course, as the profile and power masking also factors in).
Standard User TheEulerID
(learned) Sun 02-Nov-14 17:21:11
Print Post

Re: BT Infinity and line length


[re: MHC] [link to this post]
 
Judging by my (approx) 650-700m line, then I think your stats are pretty well in line with what I'd expect apart from upload, but you've explained why.
Standard User MHC
(sensei) Sun 02-Nov-14 17:46:14
Print Post

Re: BT Infinity and line length


[re: TheEulerID] [link to this post]
 
And I can get an 18+ upload if I changer router. Max attainable UP 23Mbps

An earlier set of result before the restriction: http://www.thinkbroadband.com/speedtest/button/13919...


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit

Edited by MHC (Sun 02-Nov-14 18:06:55)

Standard User MCM
(fountain of knowledge) Sun 02-Nov-14 17:55:04
Print Post

Re: BT Infinity and line length - Off Topic


[re: MrSaffron] [link to this post]
 
There is also http://maps.thinkbroadband.com/#!lat=54.628258777628... where we have calculated a speed for every postcode (outside NI) on the assumption every cabinet gets a FTTC service
Off Topic I appreciate, but I'm intrigued that your map shows FTTC/Cable speeds of 24+Mbps for the two postcodes (SW9 6UN & SW9 6UW) despite all 77+ lines in the two postcodes being EO and no VM available despite being available to the rest of the street.
Administrator MrSaffron
(staff) Sun 02-Nov-14 18:49:55
Print Post

Re: BT Infinity and line length


[re: TheEulerID] [link to this post]
 
Fully aware of the postcode area spread and also fully aware of the limiting factors of packages that people buy too.

The general aim of the map layer is to help inform ahead of the roll-outs as to what may or may not be possible. Perfection is not possible, without enabling 27 million plus lines and measuring data every few months, so one has to work with what one can produce and hopefully the map is vastly better than saying up to 80 Mbps is available just because a cabinet is present etc.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Administrator MrSaffron
(staff) Sun 02-Nov-14 18:53:03
Print Post

Re: BT Infinity and line length


[re: mikejp] [link to this post]
 
The fall off rate is pretty steep on VDSL2 hence all the moans about why different estimates can vary so much, since being 50m or 100m out on a distance estimate can mean 10 to 20 Mbps difference in speed sometimes.

There is a school of thought that also says VDSL2 does not work at all beyond 300m from a cabinet, trying to convince them is difficult, even when I can present a speed test on a 1350m line.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Administrator MrSaffron
(staff) Sun 02-Nov-14 18:57:33
Print Post

Re: BT Infinity and line length - Off Topic


[re: MCM] [link to this post]
 
A new Virgin Media layer is on the way, i.e. one I've worked out from scratch. So once that appears pester again and we can see about expanding the Virgin Media exception list

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User RobertoS
(elder) Sun 02-Nov-14 18:58:08
Print Post

Re: BT Infinity and line length


[re: MrSaffron] [link to this post]
 
And when the minimum level of interleaving, which is not uncommon, knocks about 10Mbps off the downstream, also adding 8ms to latency.

My broadband basic info/help site - www.robertos.me.uk | Domains,site and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 56.4/14.5Mbps @ 600m. - IPv4BQM IPv6BQM

"Angels can fly because they can take themselves lightly." - G K Chesterton.
Standard User TheEulerID
(learned) Sun 02-Nov-14 20:21:50
Print Post

Re: BT Infinity and line length


[re: MrSaffron] [link to this post]
 
My issue is with using it to extrapolate performance over particular length lines. Unfortunately, only Openreach will have that information insofar as there records are accurate.

What would be really nice to see (although I doubt we ever will), is a statistical analysis of the FTTC lines enabled by Openreach with estimated distance and attenuation. After all, that information is available (as it's part of the sync negotiation) and I've absolutely no doubt it's available at the DLSAM. Just how much of it is collected, I don't know, but presumably quite a lot must be to enable DLM to work.
Standard User philflyer
(member) Mon 03-Nov-14 16:17:30
Print Post

Re: BT Infinity and line length


[re: allofus] [link to this post]
 
My straight line length to the cabinet is 1400m according to google earth. For 11months I have had speeds in the region of 12mb but since a BT engineer swapped my line over it has doubled to 24mb which appears to be in line with the graph linked to by tdw42
Administrator MrSaffron
(staff) Mon 03-Nov-14 21:42:09
Print Post

Re: BT Infinity and line length


[re: TheEulerID] [link to this post]
 
In a perfect world yes that information would be available for third party analysis.

If that information was to be available I'd happily integrate it.

In the mean time we have pronouncements from areas on coverage and others doing extrapolations based on their area, so am working hard to work in the middle and am well area of the limits of the data.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Pages in this thread: 1 | 2 | 3 | 4 | >> (show all)   Print Thread

Jump to