Margin resets

OK. I posted a while back that I had a rock steady 8128 sync speed for 3 years but then out of the blue sync dropped to 7424 and stayed there.

I did battle with my ISP and a couple of days ago finally got them to get BT to drop the SNR Target margin to 12dB. As soon as they did this my router responded with an immediate resync of 8128 and stayed there solid for 48 hours with < 10 CRC errors up and down.

Almost exactly 48 hours later the router re-synced, SNR margin was back to 15dB and sync speed down to 7424, at this point the downstream error rate was increasing by approx 3 errors per second.

So my question is why? And why, given what appeared to be a steady connection with few errors over the entire 48 hour period suddenly was reverted?

I read somewhere that my margin might be quite high because my line can't reach it's 'full potential' because I'm actually too close to the exchange - is this possible?

Now I'm down to 7392 so down almost 1Mbps ... Here are my line stats again FYI:

> adsl status
--------------------------- ATU-R Info (hw: annex A, f/w: annex A) -----------
Running Mode : G.DMT State : SHOWTIME
DS Actual Rate : 7392000 bps US Actual Rate : 832000 bps
DS Attainable Rate : 7392000 bps US Attainable Rate : 1332000 bps
DS Path Mode : Fast US Path Mode : Fast
DS Interleave Depth : 1 US Interleave Depth : 1
NE Current Attenuation : 9 dB Cur SNR Margin : 15 dB
DS actual PSD : 17. 9 dB US actual PSD : 12. 4 dB
ADSL Firmware Version : 232201_A
-------------------------------- ATU-C Info ---------------------------------
Far Current Attenuation : 4 dB Far SNR Margin : 18 dB
CO ITU Version[0] : 00005453 CO ITU Version[1] : 00005443
DSLAM CHIPSET VENDOR : < TI >
>

It might be worth your while to monitor you stats.

Have a look at routerstats http://www.vwlowen.co.uk/internet/files.htm to see if your router is supported.

I have a memory of someone adding attenuation as he was too close to the exchange. Not sure if it was true or if it did any good.

Hi John,

I constantly monitor my router via SNMP (sad I know and I will remain obsessed by this until I can really understand how/why this is happening) - if someone (from BTW) could just explain it then I'd probably accept it but what my router is telling me and what is happening at the far end switch just don't see to tie up.

It could be my router has gone faulty but I did try a replacement for a short period and saw the same.

I'll dig deeper into choking the line .. seems I can't manually adjust the power on my router.

C.

Not all routers supply error stats over SNMP (my Netgear DG834G certainly doesn't). Routerstats may be able to dig out a pattern (and graph it) which you may not get from SNMP.

I had a similar problem at my house, also with an exchange that has a TI chipset.

Are you using a Vigor 2820* by any chance?

Matt

Edited by deleted (Wed 26-Aug-09 20:51:26)

Hello again Matt,

Yes indeed, a 2820n ... tried various firmware versions with little difference.

C.

In reply to a post by habile:

Hello again Matt,

Yes indeed, a 2820n ... tried various firmware versions with little difference.

C.

Here are my stats from when I had the same problem.

--------------------------- ATU-R Info (hw: annex A, f/w: annex A) -----------
Running Mode : G.DMT State : SHOWTIME
DS Actual Rate : 7360000 bps US Actual Rate : 832000 bps
DS Attainable Rate : 7360000 bps US Attainable Rate : 1336000 bps
DS Path Mode : Fast US Path Mode : Fast
DS Interleave Depth : 1 US Interleave Depth : 1
NE Current Attenuation : 6 dB Cur SNR Margin : 15 dB
DS actual PSD : 16. 0 dB US actual PSD : 12. 4 dB
ADSL Firmware Version : 211801_A
-------------------------------- ATU-C Info ---------------------------------
Far Current Attenuation : 4 dB Far SNR Margin : 18 dB
CO ITU Version[0] : 00005453 CO ITU Version[1] : 00005443
DSLAM CHIPSET VENDOR : < TI >

I ended up switching to the firmware with the 211801 modem code. You can get it at the Vigor FTP site. Let me know if you need the link.

I got the SNRM reset on the line to 12db and it held my 8128/832k sync fine from then on.

Matt

D*mn! Let me put that version back on... trouble is the ISP categorically told me they would only get BT to change the SNR target once so maybe I've missed the opportunity... I might point them at this post, it might help.

Just one thing I noticed, in the stats you posted the modem code is already 211801 isn't it?

I'm wondering if it's worth feeding this back to Draytek - sometimes that's a challenge too...

C.

In reply to a post by habile:

D*mn! Let me put that version back on... trouble is the ISP categorically told me they would only get BT to change the SNR target once so maybe I've missed the opportunity... I might point them at this post, it might help.

Just one thing I noticed, in the stats you posted the modem code is already 211801 isn't it?

They were the stats after I had changed the modem code. I never saved the stats when the problem fixed itself (as I know what sync it would be).

I had to request an SNRM change a few times until I found something that worked better for me. It can be done just might require some perseverance from your ISP to BTw.

The 211801 seems to also be the default modem code that they ship with - at least on all the Vigors I have setup.

Thanks again Matt.

I've downloaded and installed v2820_v03321_211801_A.all

I will beg the ISP to request one more SNR target reset and keep my fingers crossed. Draytek don't seem to discuss what changes in the modem firmware but this could well be the cause as the symptoms seem identical to yours - you seem even closer to the exchange!

C.

I can dig out the draytek OID's for SnR, TX Power etc.

If you work with SNMP then just walk the device and you should be able o figure it all out. The MIB's for the ADSL stuff are all in the 'transmition - adslmibs' OID tree.


If you want some example mrtg configs then PM me although I wont be able to send anything over till the end of next week due to being very busy at work at the moment.

Thanks for that. I did walk the MIB but some crucial parts of the ADSL-LINE mib are missing and I don't see errors in the MIB (other than in MIB-II but these don't reflect the CRC/Header errors on the ADSL interface).

C.