Reduced SNR = No speed increase

I've just tried reducing my SNR from 6 to 3 but I'm seeing no change in sync. Has anyone got any idea why this might be? Am I just hoping for too much? My router is a Billion Bipac 7800N and my ISP is Zen

Here's the stats from telnet before

adsl: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 8000
Max: Upstream rate = 1164 Kbps, Downstream rate = 18408 Kbps
Path: 0, Upstream rate = 1167 Kbps, Downstream rate = 14335 Kbps

Link Power State: L0
Mode: ADSL2+
TPS-TC: ATM Mode
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 6.1 5.4
Attn(dB): 26.0 14.0
Pwr(dBm): 0.0 12.9

And stats after

adsl: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 8000
Max: Upstream rate = 1172 Kbps, Downstream rate = 17336 Kbps
Path: 0, Upstream rate = 1171 Kbps, Downstream rate = 14328 Kbps

Link Power State: L0
Mode: ADSL2+
TPS-TC: ATM Mode
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 3.4 6.0
Attn(dB): 26.0 14.0
Pwr(dBm): 0.0 12.6

EDIT RE-READ WHAT YOU WROTE.

Your SNR has reduced so what I wrote was irrelevant and as such I've removed it.

Edited by ukhardy07 (Tue 01-Jan-13 18:53:43)

It's probably because the initial sync was at around 10am.

When you lowered the SNR it was probably later in the evening say 5pm.

Try resyncing with the 3db SNR at around 10 / 11am that will probably speed things up

ukhardy07 is likely correct. Warning: If he is, when you resync at 10/11am you will get a faster speed. However, around 5pm as noise increases, your SNR will probably drop to somewhere around 0 or below and you'll lose connection again.

Could well be worth it for you if you benefit more from faster speed during the day than you lose from occasional disconnections. Many people on FTTC would love the chance to make that tradeoff for themselves rather than having it imposed on them.

In reply to a post by StephenTodd:

However, around 5pm as noise increases, your SNR will probably drop to somewhere around 0 or below and you'll lose connection again.

Or more likely, if you have a good line, only drop a few tenths dB and not discon.

In reply to a post by ukhardy07:

It's probably because the initial sync was at around 10am.

When you lowered the SNR it was probably later in the evening say 5pm.

Try resyncing with the 3db SNR at around 10 / 11am that will probably speed things up

But as this is a BTW 21cn connection there are things like DLM and bras profiles at play too, Remove those factors and set the line config to fastpath , I'm failrly sure the OP would see a higher sync speed

I have heard of some ISPs locking the SNR at the line card and it cant be overidden by a router tweak, think it was reported by an Openreach guy on here or was it sync being locked for cheap 12 meg connections. Someone may confirm later.

Edited by Banger (Wed 02-Jan-13 01:54:35)

I had wrote this kind of thing initially but then deleted it.

If you look at the stats after the forcing a lower SNR the SNR actually drops from 6 to 3. If DLM had capped the sync it would have came back in at 6db.

The issue is not that throughput didn't increase, they're moaning that the actual router sync didn't go up.

The lower SNR indicates that the "tweak" went through as such.

Well since I posted this I've tried reconnecting with the reduced SNR at various times of day. But still the sync speed never increases. Could there be something stuck at the exchange end that a line profile reset might sort?

can you post a set of data at the before and after state ie normal and reduced SNR ? Done within a few minutes of each.

Hope this contains all the info you need

Default

Tweaked

As you can see, the reduced SNR actually has a slightly slower sync than the default

interesting. Does it do bit loading plots ? Seems it finds the same speed at a lower margin, which implies selection of (or preference for) less optimal tones.

Maybe someone else can answer that. Not entirely sure what you mean

On the bright side, BT have been installing fibre cabinets over the past couple of weeks

some routers show how many bits of data are allocated to each frequency band in the DSL spectrum. That might illustrate what's going on. You see a bar chart that declines in height as the frequency increases, usually - with more bits per band at the low end where SNR is best.

Ahh. I've not seen anything like that in there