OlpA
join:2007-10-26
Abilene, KS
| SN Margin
My DSL modems SN margin seems to be slowly dropping. I have at&t elite dsl service with a 2210 modem. When I first signed up my SNRM was rx 16.0 and tx 16.0. Well 6 months have went by and now my SNRM is rx 11.0 and tx 16.0. So far I have not seen a speed or quality decrease but I am worried if it keeps dropping I might start getting problems. Is this a common or do I have to do something to get my SN margin back up? |
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d_l
Barsoom
Premium,MVM
join:2002-12-08
Reno, NV
| I'm guessing that you have had numerous power cycles or re-syncs in this six months time and that the SN margin drop isn't happening during one continuous, six month-long modem sync period.
Normally a SN margin drop isn't good, but if your modem has dropped the requested output power from the DSLAM because your line is so quiet, then the SN margin drop would be reasonable.
So you have to keep an eye on the other stats as well as the SN margin OR you can check line 144 in your techreadout page. That is the maximum sync capability of your line as estimated by the modem. That value shouldn't drop over time (it might fluctuate a little from re-sync to re-sync) even if the modem requests less power from the DSLAM and the SNR margin drops as a result. |
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koma3504
Advocate
Premium
join:2004-06-22
North Richland Hills, TX | reply to OlpA
Do you here any clicking while your on your telephone??
If so then you have a bad RT/CO card or a bad connection somewhere. |
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rolande
Certifiable
Premium,Mod
join:2002-05-24
Powell, OH
clubs:
Host:
Linksys
AT&T Midwest
| reply to d_l
My SN margin for downstream is always bouncing up and down. Not a significant amount but over time it can vary by several dB. I am using a Cisco WIC-1ADSL module and I have custom MRTG script that grabs the line data for monitoring. For a long time I have averaged right at 17.5dB. Monday morning my SN margin went to -11.0 dB and of course my connection lost synch. So I went down to my equipment rack and noticed that my old POTS CAT5 patch cord that I was previously using to connect to an FXO port on my router was laying across the separate patch I use for my DSL signal. I pulled that cable so it was isolated from my DSL patch and *wham* my SN margin jumped to 20.0dB. It has never been above 18dB in the 2 and a half years I have lived here. I assume we must be getting a decent amount of AM ground noise that the POTS line is picking up. 
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d_l
Barsoom
Premium,MVM
join:2002-12-08
Reno, NV
| There is always the possibility that the OP's line has deteriorated or some in-residence, line noise source has started up. Those are the bad things that could have happened. I tried to start out checking for the good things (quieter line, lower power used) that might have occurred.  |
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OlpA
join:2007-10-26
Abilene, KS
| reply to OlpA
Thanks for the info. Line 144 has never changed at all. I will be keeping a close eye on ever thing. Also I have never heard and clicking on my phone lines. Hopefully it says the way it is and dont drop any more and I don't run into any troubles.  |
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twdallas
join:2001-02-20
Dallas, TX | I have a question over in Direct, but since we're on the topic of SN. My phone line has developed a low pitched hum last month. I haven't called to have that checked yet, but would that frequency affect the SN that you guys are talking about? |
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d_l
Barsoom
Premium,MVM
join:2002-12-08
Reno, NV
| An audible hum is a POTS problem and should be reported via 611 without mentioning that you have DSL on your phone line. The hum might be from power line interference.
Anything that degrades the POTS quality will also affect the DSL to some degree. So higher harmonics of that audible frequency might affect your DSL signal which would reduce your SN margin and increase your CRC error rate. |
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