G.DMT better than ADSL2+ ?

My exchange got upgraded to ADSL2+ about 9 months ago but my line seems to suffer from quite a lot of noise and the net result is that my download speed seems to be worse than it was before the "upgrade".

I have recently tried tweaking the settings on my router, a Zyxel P-660HW-T1 v2, and I notice that I can change the "ADSL modulation type" from ADSL2+ to gdmt so I tried this and I have noticed that the reported errors have gone from quite large amounts to practically no errors.

The sync speed has remained the same at 6656 kbps / 992 kbps but I'm hoping that BT's systems will detect the low errors and up my downlink speed from 6656 to 8128 (what it used to be prior to the upgrade).
If this does happen it will lift the BRAS rate from 5.5 to 7.15 so I live in hope!

I'm wondering if anyone else has tried this tweak and if so how long, if at all BT's systems take to increase the sync speed?

Here is a dump of the router stats if it's of any help:

P-660HW-T> wan adsl perfdata
near-end FEC error fast: 0
near-end FEC error interleaved: 0
near-end CRC error fast: 0
near-end CRC error interleaved: 0
near-end HEC error fast: 0
near-end HEC error interleaved: 0
far-end FEC error fast: 0
far-end FEC error interleaved: 0
far-end CRC error fast: 1
far-end CRC error interleaved: 0
far-end HEC error fast: 1
far-end HEC error interleaved: 0
ADSL uptime 1:21:35

P-660HW-T> wan adsl chandata
DSL standard: ADSL_G.dmt
near-end interleaved channel bit rate: 0 kbps
near-end fast channel bit rate: 6656 kbps
far-end interleaved channel bit rate: 0 kbps
far-end fast channel bit rate: 992 kbps

P-660HW-T> wan adsl linedata near
noise margin downstream: 13 db
output power upstream: 11 db
attenuation downstream: 34 db
tone 0- 31: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 32- 63: 00 00 00 02 34 45 67 78 89 9a aa bb bb bb bb bb
tone 64- 95: 0b bb ab bb aa aa ba bb ba aa aa aa aa aa aa aa
tone 96-127: aa a9 aa aa a9 a9 9a 99 99 99 99 9a 99 99 99 99
tone 128-159: 99 99 90 99 99 99 99 99 99 90 99 99 09 88 99 99
tone 160-191: 88 98 89 88 99 99 98 98 89 88 88 88 88 88 98 88
tone 192-223: 88 87 77 77 76 54 00 45 67 77 77 77 78 88 77 87
tone 224-255: 88 88 77 87 88 78 87 87 77 87 88 87 77 75 22 45
tone 256-287: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

P-660HW-T> wan adsl linedata far
noise margin upstream: 7 db
output power downstream: 19 db
attenuation upstream: 17 db
tone 0- 31: 00 00 00 35 79 ab bc cd dd dd dd dd dd dd bc 00
tone 32- 63: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 64- 95: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 96-127: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 128-159: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 160-191: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 192-223: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 224-255: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 256-287: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

If you have the option then ADSL2 (G992.3) maybe worth a try

Edited by deleted (Sun 13-Dec-09 12:23:14)

In reply to a post by rogan8:

If you have the option then ADSL2 (G992.3) maybe worth a try

Thanks for the speedy reply rogan8. I was thinking of trying ADSL2 mode (instead of ADSL2+ mode) but the router web interface did not have any way of selecting it!

I note however that the mode can also be selected via the telnet interface using the command:
wan adsl opencmd adsl2

so i tried this and my stats now look like this:

P-660HW-T> wan adsl perfdata
near-end FEC error fast: 1
near-end FEC error interleaved: 0
near-end CRC error fast: 1
near-end CRC error interleaved: 0
near-end HEC error fast: 1
near-end HEC error interleaved: 0
far-end FEC error fast: 0
far-end FEC error interleaved: 0
far-end CRC error fast: 1
far-end CRC error interleaved: 0
far-end HEC error fast: 0
far-end HEC error interleaved: 0
ADSL uptime 0:16:21

P-660HW-T> wan adsl chandata
DSL standard: ADSL2 Mode
near-end bit rate: 6656 kbps
far-end bit rate: 1083 kbps

P-660HW-T> wan adsl linedata near
noise margin downstream: 12 db
output power upstream: 11 db
attenuation downstream: 30 db
tone 0- 31: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 32- 63: 00 00 04 56 77 88 9a aa ba bb bc bb bb cc cb bb
tone 64- 95: 9a bb aa aa ab ab ba ba bb b0 aa aa aa aa 99 9a
tone 96-127: a9 99 a9 99 99 99 9a aa 9a 99 9a 9a aa a9 9a 89
tone 128-159: 99 9a 90 9a 99 88 99 99 99 90 99 98 09 88 88 88
tone 160-191: 99 88 89 88 88 88 98 98 89 88 89 88 88 88 88 88
tone 192-223: 88 77 87 77 66 54 00 35 66 66 86 78 77 77 78 77
tone 224-255: 87 77 77 87 77 77 87 87 77 78 77 76 66 65 20 45
tone 256-287: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

P-660HW-T> wan adsl linedata far
noise margin upstream: 6 db
output power downstream: 0 db
attenuation upstream: 16 db
tone 0- 31: 00 00 00 24 68 aa bc cd dd dd dd dd dd dd cc bb
tone 32- 63: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 64- 95: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 96-127: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 128-159: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 160-191: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 192-223: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 224-255: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 256-287: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Definately go with the adsl2, it operates on the same frequency as adsl1 so you don't get any more background interference, found it best on my long line

ADSL 1____G.992.1____8 Mbps_____1.1 MHz
ADSL 2____G.992.3____12 Mbps____1.1 MHz
ADSL 2+___G.992.5____24 Mbps____2.2MHz

adsl2+ would give me 1.6-1.8mb.
adsl2 gives me 2.4-2.6mb.

Edited by deleted (Sun 13-Dec-09 13:07:39)

The OP dosnt appear to have "long line" at 30dB Downstream. Would expect much better on ADSL2+, ~15Mbits all things being equal.
Maybe a 21CN router compatibility issue, or an interal wiring/filtering issue

Edited by deleted (Sun 13-Dec-09 14:54:08)

In reply to a post by rogan8:

The OP dosnt appear to have "long line" at 30dB Downstream. Would expect much better on ADSL2+, ~15Mbits all things being equal.
Maybe a 21CN router compatibility issue, or an interal wiring/filtering issue

I live 1km from the exchange and my guess is that my line is about 2km long judging from the 30db loop loss.

When I first got upgraded to ADSL2+ I got rock steady 11mb/s BRAS rate for about 3 days, then BT's systems cut in and upped my noise margin from a decent 6db to an appalling 15db, hence the bras rate dropping to 5.5mb/s. If BT detects errors on the line their systems take action and increase the noise margin. My ISP has started using BE as and alternative to BT as a LLU provider and BE lines have user configurable noise margins, but my exchange is not yet BE enabled, and I'm not sure there are plans.

Well if Be do come to your exchange I would jump on them in a heartbeat. For I have only 0.5db less attenuation than you and I get 15.5Mbps on Be and tweaking SNRM with DMT at the cost of some stability can get me another 1.5-2Mbps if I really wanted the extra.

Whoops didnt pick up on that

By tweaking on your line, you can gain extra, what I actually get. I hate you lol

Sorry, I'll hang my head in shame and look sad in sympathy