SNRM & Error levels

Hi All,

Due to some quite recent work carried out by a BT engineer, my FTTC connection appears to have become stable (regarding SNRM levels & disconnections).

However, I believe I still have quite high error levels, that may suggest there is still a problem somewhere in the D-side cabling from the cabinet.

My D-side is supposedly anywhere between 800m & 1000m in length.

From the unlocked HG612 modem's GUI, these are my current details:-

Text
1 23 45 67 89 10	DSL Up time     - 588866 (seconds) � approx 163.6 hours                    DS              US  SNRM            4.9             6.7       CRC errors      387853          0FEC errors      7167            396     HEC errors      117021          0

As a comparison, would you mind posting the DSL Up time, SNRM, & error levels as reported for your own connections, along with an estimation of your D-side line length?


Paul.

Edited by deleted (Tue 06-Dec-11 12:34:56)

Does it report Error Seconds? To get a feel for the errors you quoted I think you need to know how much data has passed.

In reply to a post by XRaySpeX:

Does it report Error Seconds? To get a feel for the errors you quoted I think you need to know how much data has passed.

It does report error seconds (somewhere else), but I was simply trying to obtain a general overall feel for TYPICAL connections.

e.g. for my connection:-
Line length 800m to 1000m.
DS SNRM = 4.6 dB, US SNRM = 6.8 dB.
DSL up time of 610696 seconds is roughly 169.64 hours.
389814 DS CRC errors in that period AVERAGES at 2298 CRC errors per hour.

From another user:-
Line length ????
DS SNRM = 22.4 dB, US SNRM = 21.9 dB.
DSL up time of 6231232 seconds is roughly 1731 hours.
144 DS CRC errors in that period AVERAGES at only 0.08 CRC errors per hour.

A massive difference between the 2 connections is clearly seen.

That's basically what I'm trying to establish, in simplistic terms, to help confirm what a typical connection, over typical line lengths could be expected to achieve (or not achieve).


Paul.

P.S. Quite a lot of the errors being reported for my connection occur overnight, while I'm tucked up in bed & the PC is not being used (apart from the occasional programmed software updates.
The errors don't really coincide with these events.

That's an invalid comparison with another line that has massive noise issues, witnessed by:

DS SNRM = 22.4 dB

Anyway you can't average errors over time, only over quantity of data.

Mine's been up for about 10 days (246 hours) since last modem reboot. Sadly its a Fritz so doesn't show the same detail, but I think of it as a poor line (600m+ with something like over 50 repair joints between me and the cab!), and, of course, heavily interleaved::

Receive Direction / Send Direction
Max. DSLAM throughput kbit/s 40000 / 7200
Min. DSLAM throughput kbit/s 20000 / 3600
Attainable throughput kbit/s 42060 / 5611
Current throughput kbit/s 39992 / 5608

Latency 8 ms / 0 ms
Bitswap on / on
Impulse Noise Protection 3.0 / 0.0

Signal-to-noise ratio dB 7 / 6
Line attenuation dB 20 / -
Carrier record A43 / A43
Profile 17a

FRITZ!Box:
Error seconds 2295
Many ES 1
Remediable Errors (FEC) per minute 2344
Last15 minutes 8467540
Not Remediable Errors (CRC) per minute 0.47
Not Remediable Errors (CRC) last 15 minutes 8

DSL central exchange
Error seconds 784
Many ES 0
Remediable Errors (FEC) per minute 1
Last15 minutes 2
Not Remediable Errors (CRC) per minute 0.05
Not Remediable Errors (CRC) last 15 minutes 0

On a typical day the unrecoverable errors seem to jump between 2 and 4 x the usual for an hour once in the early morning and once late afternoon to 124, strangely when I'm not using the connection. EDIT: I've not noted any significant change in the reported errors on heavy downloading (up to 35Mbps) but I can see the upload band is restricted.

Edited by deleted (Tue 06-Dec-11 21:17:20)

Couldn't the premises be very close to the cabinets? That would send the margin high.

In reply to a post by XRaySpeX:

Anyway you can't average errors over time, only over quantity of data.

That is an interesting comment, XRay. How would you (assuming possession of equipment that provides basic statistics on everything) quantify errors in such a way that they may be plotted on a graph, for instance?

Edited by burakkucat (Tue 06-Dec-11 21:44:58)

In reply to a post by XRaySpeX:

That's an invalid comparison with another line that has massive noise issues, witnessed by:

DS SNRM = 22.4 dB

Anyway you can't average errors over time, only over quantity of data.

Hmm,

The line with the massive noise issues & hardly any errors in comparison with mine syncs at 39999 K & 10000 K.
Its attainable rates are 95252 K & 33134 K.

Mine, with a very low SNRM but thousands more errors in comparison, syncs at only 27942 K & 5679 K.
My attainable rates are only 30756 K & 5961 K

Currently, the maximum speed I can actually download at is just over 26000K

I also believe I did average the errors over time.
A few thousand errors per hour for my connection, compared to much less than 1 error per hour for the other user's connection.

I concede these are only averages as I often get much less per hour, but by the same token, I occasionally get many, many more per hour.

I am no doubt further from the cabinet than the other user as my attenuation is also incredibly high, but I wasn't really discussing that aspect at this time.

Have you any explanation as to why my connection occasionally experiences up to 90000 DS CRC errors within a 2 minute period, especially when it is unattended & not downloading/uploading anything that I am aware of? I haven't.

I'm also not 100% sure that programs such as RouterStats compare errors against the quantity of data either.

Just as an experiment, I have repeatedly downloded a 15 Mb test file - no errors whatsoever, yet 1/2 hour ago, while I wasn't even at the PC, my records show over 300 DS CRC errors within a 2 minute period.

I can't explain that either. Can you?

To help me understand your comment a little better, is there any chance of you humouring me by providing your error counts & SNRM levels over whatever duration your FTTC connection has been up, also confirming the quantity of data you have downloaded/uploaded during that period?

EDIT:
Do these figures mean anything to you?
I have to admit they don't mean a lot to me:-

Text
1 23 4	ES:             1019            271 SES:            11              0UAS:            15              15 AS:             631461

Edited by deleted (Tue 06-Dec-11 23:03:26)

If I had to think about it, I would plot "SFErr/SF" (%CRC), "HEC/Total Cells" and "RSUnCorr/RS" (%FEC) against time, using the terminology of Netgear (ignoring diff error terminology for diff routers which others more knowledgeable than me can translate).

Don't know how much help it will be, probably just some more data to compare.

These are the errors after about 45 minutes (rebooted it earlier), roughly it ends up being about 200 - 100 on both FEC and HEC errors after a day or so.

Never seen any CRC errors on the line in the 2 weeks I've had access to the modem and the line length is approximately 600m.

Downstream Upstream
Line rate (kbit/s) 39998 10000
CRC errors 0 0
FEC errors 4 2
HEC errors 4 0