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Message 21 of 31

Re: Jargon And The Real Picture

This thread is getting complex and is danger of confusing several issues.

 

The connection from your home to the cabinet is a phoneline which can be 50 years old or more. The speed you get is Dependant on the quality of that line and its length. The kit in the cabinet controls the speed to minimise errors and ensure a stable connection - you can see what that speed is by looking at the IP profile reported by the BT Speedtester. The cabinet is not managing bandwidth overall only each connection. A good line can in theory deliver in excess of 100 Mb/s but is currently limited to 40 Mb/s soon to be changed to 80 Mb/s. 

 

From the cabinet to the exchange is handled by fibre which has more than adequate capacity. At the exchange the traffic passes to BT Wholesale's backhaul which carries the traffic to the wider internet. Users share that capacity and it is the contention within isps networks that cause issues at busy times. BT seem quite good here in comparison with Virgin for example. I was with Sky before who are good but BT seem to be just as good - ignoring traffic management of p2p which I don't use!

 

My own experience is on a cabinet that is nearly full according to OR's engineers as it was fitted 18 months back in an area where ADSL delivered around 2 Mb/s at best. So if anyone was seeing issues it would be here. I have just run a speed test at 36.61mb/s at 6am I may see 38Mb/s so actually BT are delivering. Services such as HD iplayer or Onlive gaming run without issue so Infinity works for me and my neighbours but your experience may vary.

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Message 22 of 31

Re: Jargon And The Real Picture

As is said earlier full sized cabs are limited to 288 connections so it will never strain the fibre
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Message 23 of 31

Re: Jargon And The Real Picture

Just to add my max attainable rate is just over 132000kbps, which is nice lol
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Message 24 of 31

Re: Jargon And The Real Picture

Hi, Infinitechris,

 

many thanks...your reply was what I was hoping somebody would post.  It clarifies some points, fundamental to understanding why things are like they are, but it also begs other questions...

 

If the FO cable, (exchange - cabinet) has 'more than adequate capacity', that presumably means it's easily able to service the 288 lines in the cab at up to 40Mbps (at present) and later, up to 80Mbps? the copper to the house being the limiting factor.

 

If a new housing estate is developed in the area...God forbid, additional cabinet(s) are installed?  Or is there a hybrid cabinet that contains both the FO to exchange and copper to the customer interfaces?

 

Do you see bt developing FO to the house at an affordable price?

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Message 25 of 31

Re: Jargon And The Real Picture

The FO to the house you mention is known as FTTP, fibre to the premises, BT have trialled it in a few areas for nearly a year and recently launched it as Infinity option 3 with 100/15 speeds. But you have to live in one of the few areas they are doing FTTP in order to get it. 

 

As with the FTTC rise to 80meg I think the FTTP speed is going to rise to 300meg.

 

As to costs when my time on the trial ends, currently due in April when the FVA, fibre voice access, telephone on fibre, I am expecting to be offered all 3 Infinity options at the standard prices but will stay connected by the FTTP already here as there are no cabinets fitted in the streets. 

 

How may other exchanges get added to the few doing FTTP is anyones guess but at the moment I think that is the way ahead. But then what do I know. I think they need a certain type of infrastructure in place already to be able to get the fibre to your premises, the right type of ducting or poles etc, changing all of these too would I imagine spiral the install costs.

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Message 26 of 31

Re: Jargon And The Real Picture

I don't know off hand the spec of the optical fibre used from the exchange but the standard cabinet has 288 connections and as yet I have not seen any reports where a second cabinet has been fitted to a PCP. Various ideas are around to add extra capacity by adding additional "top cabinet" etc I would think the limiting capacity will be the power supply and batteries in the fibre cabinets. Some people report seeing cabinets where only half the rack has been fitted intially. Smaller PCPs round here have the 144 connection cabinets. 

 

When new build happens you require both a PCP for the phone line and a fibre cabinet. Many new build estates require new PCPs as there is insufficent capacity on the existing ones and up until now these later PCPs have not automatically got fibre cabinets. Its a frequent complaint that somebody buys a new house on a development in a fibre area but cannot get fibre. It maybe that BT require cash from the developer to make that happen and where they don't get it they won't pay themselves who knows. As regard hybrid cabinets it seems a reasonable idea but PCPs do not contain power and are worked on in all weathers which I suspect that may be a little challenging for delicate DSLAMS etc.

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Message 27 of 31

Re: Jargon And The Real Picture

FTTP...I was trying to stay with plain English!  Smiley Wink

 

To clarify...the 100/15 service or Infinity option3, is 'up to'!  I can imagine very few 'copper customer's' lines will ever attain 100Mpbs download.

 

Looking ahead...What's the domestic customer going to do with 300Mbps?  I'm not sure where the perception threshold is, at which point the response at the customer interface appears to be instantaneous.  It would seem to be when the demand for data is at it's heaviest...downloading a full length feature film, maybe?  I can imagine 300Mbps would appear pretty quick... an average size feature film downloaded in just over a minute !  If my calculations are right then we're looking at several Tbps before 'instantaneous becomes the norm?  This would certainly be the objective for military or commercial systems and is doubtless, already being achieved with more complex and expensive transmission systems.

 

 

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Message 28 of 31

Re: Jargon And The Real Picture

BT's routers to the backhaul only have gigabit connections (even sub-Atlantic fibres are only tens of gigabits in capacity), so there will always be a bottleneck at those points...

 

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Message 29 of 31

Re: Jargon And The Real Picture


@loopfish wrote:

BT's routers to the backhaul only have gigabit connections (even sub-Atlantic fibres are only tens of gigabits in capacity), so there will always be a bottleneck at those points...

 


Is that a physical or a financial limitation?

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Message 30 of 31

Re: Jargon And The Real Picture

Financial. No isps have networks that can take all customers being active at once and do not need to. This used to be referred to as the contention ratio with maybe 1000 users sharing a pipe which has the capacity for 50 of those users to get full speed a ratio of 20 to 1. Bandwidth is expensive and the cost of Infinity is far less than a leased line where contention would be much lower and you get what you pay for in data transmission. In practice it works very well as statistically few people max out connections for very long periods so a few heavy users are balanced by light users and so on, there is quite an industry in specifying networks. 

 

In fact BT seem to have most of the calculations about right excluding a few exchanges as the speeds have been reasonable and better than many people expected. Certainly they are significantly cheaper than anyone who might be better.

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