SNR / Loop attenuation typical values?

[Inkblot]

I posted here recently regarding a high number of RX CRC errors showing in my router stats, the router has now been swapped for a spare and now (After being up for 35 minutes) I have the only 31 RX CRC errors and following stats:

Mode                 State           Up       Down     SNR Loop Att.
ADSL2+(G.992.5) SHOWTIME 824000 10996000   5       39

Formerly I was getting 400-500 RX CRC errors every 10 seconds and had an SNR margin of 2

For comparison, some of our other sites show the following:

Mode                 State           Up       Down     SNR Loop Att.
G.DMT                SHOWTIME 832000 7616000   13     35
G.DMT                SHOWTIME 832000 8128000   12     25
G.DMT                SHOWTIME 832000 5632000    6      44
ADSL2+(G.992.5) SHOWTIME 1127456 9432727  14     37

So a range of 5-14 on SNR and 25-44 on loop attenuation, the 2 red coloured circuits are in the same physical building - in the same server room in fact! The blue circuit is located 100m away but on the same physical exchange and quite probably in the same street cabinet, the other sites are on different exchanges.

Are spreads of values like this commonplace? What are typical SNR and loop attentuation values?

2 of these circuits are with IDNet, the others will be at some point but not just yet - I'm waiting for contract periods to end

[DorsetBoy]

SNR and attenuation are very different on ADSL Max and ADSL2+ which explains the difference you see for the red examples.

[Inkblot]

My main concern is that although the line maintains a connection from the Internet (It hosts a terminal server for access to one of our primary systems) we frequently get timeouts and dropped terminal sessions. This isn't helped by the fact that we are also running an SMTP server on the same link although within a few weeks this will be moved elsewhere. I found some stuff regarding SNR and Loop attenuation, obviously ADSL rather than ADSL2 or 2+ but I ssuspect the bit about the SNR margin may still be relevant

SNR is Signal to Noise Ratio (aka Noise Margin or Signal to Noise Margin)
Relative strength of the DSL signal to Noise ratio. 6dB is the lowest dB manufactures specify for modem to be able to synch. In some instances interleaving can help raise the noise margin to an acceptable level. The higher the number the better for this measurement.

6dB or below is bad and will experience no synch or intermittent synch problems
7dB-10dB is fair but does not leave much room for variances in conditions
11dB-20dB is good with no synch problems
20dB-28dB is excellent
29dB or above is outstanding

Loop Att. is Line Attenuation
Measure of how much the signal has degraded between the DSLAM and the modem. Maximum signal loss recommendation is usually about 60dB. The lower the dB the better for this measurement.
20dB and below is outstanding
20dB-30dB is excellent
30dB-40dB is very good
40dB-50dB is good
50dB-60dB is poor and may experience connectivity issues
60dB or above is bad and will experience connectivity issues

Incidentally, my SNR seems to fluctuate between 2 and 6 although attenuation is steady at 39. My RX CRC errors (After 2hrs) is a 78 which is much better than previous but I did get quieter periods so maybe tomorrow will show a different story

[Lance]

6dB or below is bad and will experience no synch or intermittent synch problems
7dB-10dB is fair but does not leave much room for variances in conditions
11dB-20dB is good with no synch problems
20dB-28dB is excellent
29dB or above is outstanding

That must have been an old source, as that pre-dates ADSL Max! On Max, the default noise margin target is 6db. You shouldn't lose sync until you get to 0db (or 1-2db if the modem is a bit sensitive).

With regards to attenuation, its rare for this to fluctuate widely. Normally, throughout the course of the year you will see minor (no more than 2-3db) movement as the outdoor temps change between winter and summer.