In reply to a post by WWWombat:

We are 400 metres from the cabinet, by the shortest possible (and most likely) road route. We get a full 80/20 sync.

The kind of numbers that you are being predicted would match a line length of over 1km - perhaps nearer 1500m (assuming copper lines). Is it possible that you are connected to a different cabinet? You aren't always connected to the closest one.

One way to find out which cabinet, and get a better idea of dates, is to question Openreach themselves. Their email is given in the FAQ on this page... something like nga.enquiries@...

TBH that's more akin to an estimate on a 5.5+ KM line. Various lines I know to be over 5KM in length have estimates of 1.5 ~ 3 Mbit on the BT Wholesale checker.

It may simply be that the lines have poor composition - they may be lead, aluminium, some antiquated alloy, any number of things especially considering it's a rural area.

Doesn't even have to be a rural area. My mother used to live only 1.9KM from the exchange but couldn't get more than 3Mbit due to a high quantity of aluminium and thin guage copper in the line. I'm half a kilometer further from the same exchange and get over double the speed.

As others have said though, may just be the checker being pessimistic. Good luck!

In reply to a post by izools:

TBH that's more akin to an estimate on a 5.5+ KM line. Various lines I know to be over 5KM in length have estimates of 1.5 ~ 3 Mbit on the BT Wholesale checker.

We're talking about the FTTC predictions here, not the ADSL ones.

We're not going to get VDSL2 to work over 6km!

In reply to a post by WWWombat:

In reply to a post by izools:

TBH that's more akin to an estimate on a 5.5+ KM line. Various lines I know to be over 5KM in length have estimates of 1.5 ~ 3 Mbit on the BT Wholesale checker.

We're talking about the FTTC predictions here, not the ADSL ones.

We're not going to get VDSL2 to work over 6km!

Doesn't matter what the DSL protocol is, at 1500M actual line length the sync rate is going to be circa 20 Meg; dependent on line composition.

VDSL2 deteriorates quickly from a theoretical maximum of 250 Mbit/s at source to 100 Mbit/s at 0.5 km (1,600 ft) and 50 Mbit/s at 1 km (3,300 ft), but degrades at a much slower rate from there, and still outperforms VDSL. Starting from 1.6 km (1 mi) its performance is equal to ADSL2+.[3]

Edited by deleted (Sat 20-Oct-12 04:34:32)

I don't know where you got that quote from, but in practice it seems to be not true.

Downstream is definitely well below 20Mb before 2km. However, it seems that the upstream speed is most limiting - and that runs out first, so that VDSL2 is no use whatsoever. I believe someone posted their stats on here, showing upstream to be very slow on a sub-2km line.

Some further corroborating evidence on this TBBnews article (speeds at DR) and in the pdf's on this old thread

In reply to a post by WWWombat:

I don't know where you got that quote from, but in practice it seems to be not true.

Downstream is definitely well below 20Mb before 2km. However, it seems that the upstream speed is most limiting - and that runs out first, so that VDSL2 is no use whatsoever. I believe someone posted their stats on here, showing upstream to be very slow on a sub-2km line.

Some further corroborating evidence on this TBBnews article (speeds at DR) and in the pdf's on this old thread

Fair enough. I will disregard that part of the VDSL2 Wikipedia article then!

I suppose the difference is likely to be the boundary between the last upstream BIN and the first downstream BIN on the frequency spectrum. It's a pity Openreach haven't configured their DSLAMs to support auto-fallback to ADSL 2+, 2, or 1.

In reply to a post by izools:

Doesn't matter what the DSL protocol is, at 1500M actual line length the sync rate is going to be circa 20 Meg; dependent on line composition.

VDSL2 deteriorates quickly from a theoretical maximum of 250 Mbit/s at source to 100 Mbit/s at 0.5 km (1,600 ft) and 50 Mbit/s at 1 km (3,300 ft), but degrades at a much slower rate from there, and still outperforms VDSL. Starting from 1.6 km (1 mi) its performance is equal to ADSL2+.[3]

That's a very accurate prediction (at least for this line..)

The loop length, according to TDR, is 5200ft (just shy of 1600 metres).

http://asbokid.picturepush.com/showformat.php?&alid=...

Openreach just did a great job repairing a noisy intermittent short and the ADSL2+ sync rate is now ~20Mbps.

http://asbokid.picturepush.com/showformat.php?&alid=...

cheers, a


edit: one day i might post a URL that actually works! *sigh*

Edited by deleted (Sun 21-Oct-12 13:42:43)

There is no boundary like in the sense of G.DMT

There are blocks of bins such that the upstream is not a single contigous block occuping the lowest frequency bins, but is split into two of three blocks across the 17MHz.

Hence why upstream tails off. Can't find the bin plot screenshot I have somewhere showing this.

See the Discovery and Medley phases. IIRC most show the Medley/Final as a missing a few frequencies compared to the Discovery.

# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Max:    Upstream rate = 13963 Kbps, Downstream rate = 58032 Kbps
Path:   0, Upstream rate = 14641 Kbps, Downstream rate = 57485 Kbps

Discovery Phase (Initial) Band Plan
US: (0,95) (868,1207) (1972,2783)
DS: (32,859) (1216,1963) (2792,3959)
Medley Phase (Final) Band Plan
US: (0,95) (868,1207) (1972,2783)
DS: (32,859) (1216,1963) (2792,3959)
       VDSL Port Details       Upstream        Downstream
Attainable Net Data Rate:      13963 kbps         58032 kbps
Actual Aggregate Tx Power:        6.6 dBm          13.4 dBm
============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3
  Line Attenuation(dB):  5.3     29.6    44.5     N/A    14.4    36.3    55.7
Signal Attenuation(dB):  8.9     28.5    43.3     N/A    14.4    36.3    55.7
        SNR Margin(dB):  5.9     5.7     5.7      N/A    6.1     6.1     6.2
         TX Power(dBm): -3.9    -12.8    6.3      N/A    11.1    7.9     4.2

Edit - Hmmmm. The first band starts seem to overlap. That can't be right.

Edited by RobertoS (Sun 21-Oct-12 12:07:05)

In reply to a post by MrSaffron:

There is no boundary like in the sense of G.DMT

There are blocks of bins such that the upstream is not a single contigous block occuping the lowest frequency bins, but is split into two of three blocks across the 17MHz.

Hence why upstream tails off. Can't find the bin plot screenshot I have somewhere showing this.

Like this one from taken from my modem. Bit Loading Plot

In reply to a post by RobertoS:

See the Discovery and Medley phases. IIRC most show the Medley/Final as a missing a few frequencies compared to the Discovery.

# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Max:    Upstream rate = 13963 Kbps, Downstream rate = 58032 Kbps
Path:   0, Upstream rate = 14641 Kbps, Downstream rate = 57485 Kbps

Discovery Phase (Initial) Band Plan
US: (0,95) (868,1207) (1972,2783)
DS: (32,859) (1216,1963) (2792,3959)
Medley Phase (Final) Band Plan
US: (0,95) (868,1207) (1972,2783)
DS: (32,859) (1216,1963) (2792,3959)
       VDSL Port Details       Upstream        Downstream
Attainable Net Data Rate:      13963 kbps         58032 kbps
Actual Aggregate Tx Power:        6.6 dBm          13.4 dBm
============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3
  Line Attenuation(dB):  5.3     29.6    44.5     N/A    14.4    36.3    55.7
Signal Attenuation(dB):  8.9     28.5    43.3     N/A    14.4    36.3    55.7
        SNR Margin(dB):  5.9     5.7     5.7      N/A    6.1     6.1     6.2
         TX Power(dBm): -3.9    -12.8    6.3      N/A    11.1    7.9     4.2

Edit - Hmmmm. The first band starts seem to overlap. That can't be right.

Part of the lower band can be shared apparently. They show up on the bit loading plot I posted above.

Edited by simon194 (Sun 21-Oct-12 16:06:13)