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Standard User homer79
(newbie) Sat 02-Jul-11 23:33:34
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BT's 80Mb increase


[link to this post]
 
hi,

I know that bt are moving to profile 17a, does anybody know if they are letting the transmit power increase as well? or are they running it at a lower power. 8c allows for 11.5dB out, where as 17a allows for 14.5dB. which means the output power is doubled.
Standard User MHC
(legend) Sun 03-Jul-11 00:18:31
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Re: BT's 80Mb increase


[re: homer79] [link to this post]
 
Total power is doubled but that does not mean the power at each frequency is ... as the spectrum spreads further up there is power in the higher frequencies which is where the increase comes from.





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Standard User WWWombat
(committed) Sun 03-Jul-11 03:40:12
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Re: BT's 80Mb increase


[re: MHC] [link to this post]
 
They have to employ a PSD mask, to restrict the power output where it can affect ADSL and ADSL2+ signals coming from the exchange - and have to reduce power more when the cabinet is further from the exchange, as the ADSL signals will be at a lower level by then.

For the extra frequencies above ADSL2+, the cabinet can use the "proper" power levels.

Trefor's site quotes BT as saying that the new profile will allow for greater range, even though only the closer properties will benefit from the higher frequencies - this suggests that there could well indeed be some higher powers involved!


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Standard User adebov
(eat-sleep-adslguide) Sun 03-Jul-11 07:53:44
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Re: BT's 80Mb increase


[re: WWWombat] [link to this post]
 
In reply to a post by WWWombat:
and have to reduce power more when the cabinet is further from the exchange, as the ADSL signals will be at a lower level by then.

For the extra frequencies above ADSL2+, the cabinet can use the "proper" power levels.

Does it follow, then, that on cabinets which are a very long way from the exchange BT can increase vDSL power above regular ADSL1 frequencies (possibly even lower) because here nothing on ADSL1/2/2+ above about 800kHz gets through anyway?

My line is supposedly 6.9km, but is actually 5.3km, and I'm around 160m from the exchange - meaning none of the lines can be shorter than around 5.1km, so what's the point holding back power on vDSL frequencies between 800kHz & 2Mhz, when they can't make it down a 5km cable in the first place.

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Standard User homer79
(learned) Sun 03-Jul-11 12:14:45
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Re: BT's 80Mb increase


[re: WWWombat] [link to this post]
 
on my exchange there is no ADSL2. I really cant see BT making different profiles up for each cabinet. But i could see them employing different profiles for where ADSL2 does exist and where it doesn't.
In an area that is near me, the FTTC rolled out in February has had a really negative effect on the ADSL connections.
Standard User WWWombat
(committed) Sun 03-Jul-11 15:15:09
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Re: BT's 80Mb increase


[re: adebov] [link to this post]
 
Yes, the mask changes based on the (electrical) distance from the exchange. The changes do adjust for a maximum frequency that is expected to be still usable at that distance.

Look at page 31 in this primer.

If your cabinet were assigned a CAL of 52dB, it would be able to use (I guess) extra power from 600kHz up. If the CAL were 40dB, it would be at 900kHz.

Edited by WWWombat (Sun 03-Jul-11 15:21:05)

Standard User WWWombat
(committed) Sun 03-Jul-11 15:30:13
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Re: BT's 80Mb increase


[re: homer79] [link to this post]
 
They do have different profiles, based on the electrical distance of the cabinet from the exchange. The graph in the document I linked to above has 7 profiles.

The profiles apply to both ADSL and ADSL2+, and take account of the maximum frequency expected to be able to get out as far as that particular cabinet. The furthest 3 profiles all allow VDSL2 to be using power on frequencies above 900 kHz, so they already discount the worth of the extra frequencies in ADSL2+.

I haven't seen a mention of different profiles based on there only being ADSL available.

The mask are the rules set in the ANFP, so increasing power for a cabinet that has no ADSL (or 2+) is possible, but requires an exemption from NICC. I've seen Rutland mention that they might choose to request such an exemption if they installed a fibre cabinet and converted everyone. I'd imagine an exemption for a cabinet that has just ADSL (no 2+) is possible - but could be risky, if BT chose to install exchange-based 2+ at a later date.
Anonymous
(Unregistered)Sun 03-Jul-11 15:41:53
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Re: BT's 80Mb increase


[re: WWWombat] [link to this post]
 
Indeed. I cant see BT putting the manpower into calculating between non adsl2 exchanges and those that are - they could implement such changes only to find a week later that an LLU provider unbundles the exchange..

Actually... Isnt 21cn (i.e. adsl2) a prerequisite of fttc anyway? Surely then no cab will the be adsl max only? unless the fibre cab is fed via another exchange...
Standard User Ribble
(member) Sun 03-Jul-11 15:51:08
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Re: BT's 80Mb increase


[re: Anonymous] [link to this post]
 
unless the fibre cab is fed via another exchange...

I think most exchange areas are as it reduces the number handover points (head ends)
Standard User RobertoS
(sensei) Sun 03-Jul-11 15:51:28
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Re: BT's 80Mb increase


[re: Anonymous] [link to this post]
 
There are several cases where the fibre cab is fed from a different exchange which has WBC. WBC is not a requirement at the PCP's exchange, though of course that is the normal setup.

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