Profile 17a - U/S worse?

In case anyone hadn't noticed it's official tha BT are upgrading to Profile 17a - sadly I think that they are going to keep on Band Plan 997 which is a bit of a pain on mid-length lines.

Checked the modem this morning - "attainable" now up to ~49000 Kbs^-1, sync at 39999 Kbs^-1. It had settled to ~37000 Kbs^-1 recently on 8c (apart from an odd week where it held 40M but at a 3dB margin following an overnight resync - I did wonder whether the DLM would set a 3dB margin but no dice; it reverted to 6dB at the next resync).

Here's the odd thing though - my U/S attainable has fallen from ~17Mbs^-1 to 11 or so. Given that the 17a adds an upstream block first (from 7.05MHz to 12MHz) I had expected to see U/S well above 20M.

Must get some graphs and have a look what's going on but in the meantime anyone have any ideas?

In reply to a post by mr_bean:

In case anyone hadn't noticed it's official tha BT are upgrading to Profile 17a - sadly I think that they are going to keep on Band Plan 997 which is a bit of a pain on mid-length lines.

They are moving to Band Plan 998

They are moving to Band Plan 998

OK, have telnetted in had a closer look and dug out the old stats - you are, indeed, correct. [edit] Oh, and I can see that this has already been discussed on the "Strange speed increase" thread - apologies for not keeping up

I now get

xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason:	0
Max:	Upstream rate = 11817 Kbps, Downstream rate = 49388 Kbps
Path:	0, Upstream rate = 10000 Kbps, Downstream rate = 39997 Kbps

Discovery Phase (Initial) Band Plan
US: (0,95) (868,1207) (1972,2783) 
DS: (32,859) (1216,1963) (2792,3939) 
Medley Phase (Final) Band Plan
US: (0,95) (868,1207) (1972,2783) 
DS: (32,859) (1216,1963) (2792,3939) 
       VDSL Port Details       Upstream        Downstream
Attainable Net Data Rate:      11817 kbps         49388 kbps
Actual Aggregate Tx Power:        6.5 dBm          12.6 dBm
============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3
  Line Attenuation(dB):	 6.5	 33.2	 48.3	  N/A	 16.2	 40.3	 61.4	
Signal Attenuation(dB):	 9.5	 32.3	 47.2	  N/A	 16.2	 40.3	 61.4	
        SNR Margin(dB):	 8.0	 8.1	 8.1	  N/A	 10.3	 10.4	 0.0	
         TX Power(dBm):	-4.4	-11.8	 6.1	  N/A	 10.7	 7.9	-128.0

It looks to have given up on D3 altogether given the 61.4dB attenuation so basically I'm just benefiting from the fact that the D2 tones now go from 1216 to 1973 compared to 1192-1627 previously. I remain slightly surprised that U/S attainable hasn't improved given that U2 should now come into play (albeit at 48dB attenuation)

It's a good move on my line - gives me back max sync and some overhead against crosstalk. Not much point me going for 80/20* but I'm happy at 40/10 compared with 3Mbs^-1 on ADSL.

*might have done if the U/S had improved even if the D/S didn't change much.

Edited by mr_bean (Thu 10-Nov-11 10:43:49)

Just had a look at your original link - and it is conformed in there too.

Interesting results. What distance are you from the cabinet?

My line is similar, and has gained 2-4Mbps in Downstream speed since (I think) they introduced 17a, but has retained the full uplink speed. I'm about 600-650m from the cabinet.

From your modem stats, I'd guess you have a little room to go beyond 40Mbps. It looks like it has chosen to distribute the required 40Mbps to give an SNR of 10dB. It could well be that some of D3 would get used if it needed to push the SNR down to 6dB, while both D1 and D2 seem to have 4 dB's capacity left.

I think I need to unlock my modem too, and find the detailed figures

On the ANFP: it has a history indicating:
- Issue 5 (V5.1.0)
- September 2011
- Revised to accommodate plan VDSL2 998ADE17 and include frequencies up to 17MHz. VDSL2 profile 997-M1c-A-7 8c is deprecated.

I also remember an old BT document (2009, when they first played with VDSL2) stating that it is impossible to run both plan 997 and 998 within the same plant, because of interference problems.

Taken together, I suspect that means the entire FTTC deployment will shift to 998+17A, with nothing left on the 997 band.

Interesting results. What distance are you from the cabinet?

Approx 600-650m (it's 560m in a straight line so not less than that).

FTTC since April - original sync 39997, attainable 42M ish (from engineer's JDSU). Stayed that way for a while (initial figures from unlocking the modem very similar) but then I seemed to acquire a 3dB noise increase - oddly coincidental with the original modem dying but I still presume it must have been increased crosstalk.

From your modem stats, I'd guess you have a little room to go beyond 40Mbps. It looks like it has chosen to distribute the required 40Mbps to give an SNR of 10dB. It could well be that some of D3 would get used if it needed to push the SNR down to 6dB, while both D1 and D2 seem to have 4 dB's capacity left.

Attainable 48M at the moment which from observation is at a 6dB SNRM. I wonder if there is anything extractable from D3 - my ADSL line managed 3Mbs^-1 on 63dB attenuation but I'm not sure you can draw any conclusions from that.

I also remember an old BT document (...) stating that it is impossible to run both plan 997 and 998 within the same plant, because of interference problems.

I'd certainly expect it to be impossible - upstream and downstream bands overlap between the two band plans. That would mean modems in one band plan transmitting on frequencies that modems on the other band plan would be trying to receive - the near end crosstalk would be huge.

your line looks very similar too mine

# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Max: Upstream rate = 12014 Kbps, Downstream rate = 50444 Kbps
Path: 0, Upstream rate = 10000 Kbps, Downstream rate = 39996 Kbps

Discovery Phase (Initial) Band Plan
US: (0,95) (868,1207) (1972,2783)
DS: (32,859) (1216,1963) (2792,3939)
Medley Phase (Final) Band Plan
US: (0,95) (868,1207) (1972,2783)
DS: (32,859) (1216,1963) (2792,3939)
VDSL Port Details Upstream Downstream
Attainable Net Data Rate: 12014 kbps 50444 kbps
Actual Aggregate Tx Power: 6.6 dBm 11.8 dBm
============================================================================
VDSL Band Status U0 U1 U2 U3 D1 D2 D3
Line Attenuation(dB): 5.6 31.4 45.9 N/A 15.3 38.9 59.7
Signal Attenuation(dB): 7.3 30.6 44.7 N/A 15.3 38.9 59.7
SNR Margin(dB): 7.7 7.7 7.7 N/A 7.0 7.1 7.4
TX Power(dBm): -3.9 -13.3 6.3 N/A 8.1 7.9 4.3


thing is it used to only sync at approx 30000kbps downstream and 8000kbps up

In reply to a post by WWWombat:

I think I need to unlock my modem too, and find the detailed figures

Go on WWWombat, just do it. You know you want to

Paul.

Wait for them to enable vectoring in 2012. This should boost speeds considerably and might take your upload speed back up to the 20Mb mark.

In reply to a post by Bald_Eagle1:

Go on WWWombat, just do it. You know you want to

Paul.

I do, but SWMBO would go mental if I broke it. I need enough time to unlock it *and* to put it right again if I b***er things up