As seen in this post by dynodb : »Intermittent Disconnects and Lag, Qwest DSL

These are the stats I'd mainly look at:

Speed (down/up): 1536 / 736 Kbps
Near End CRC Errors (I/F): 2/0
Far End CRC Errors (I/F): 2/0
Near End RS FEC (I/F): 1224/0
Far End RS FEC (I/F): 2499775/0
SNR Margin (Downstream/Upstream): 6/6
Attenuation (Downstream/Upstream): 63/63

The speed tells you what you're trained at. That he's trained at under the maximum rate of 896 or 1024k says that the modem and DSLAM couldn't connect at a higher rate without the SNR dropping below 6dB.

Errors- near end are those recieved at the modem, far end are those reported by the DSLAM. CRC's are uncorrectable errors, FEC errors are those corrected through interleaving. You'll always see at least a couple of errors, but if they increment heavily, it's likely going to be a problem.

SNR margin- Signal to Noise Ratio margin. This is the SNR above the minimum SNR needed to sustain a certain speed. If it takes 20dB to connect at a given speed, and the actual SNR is 26dB, you will have an SNR margin of 6dB.

6dB is the minimum SNR margin that Qwest DSLAMs are configured to train at. 6dB is marginal but not necessarily a deal-killer. Plenty of people are trained at 6dB with nothing more than some errors that don't cause noticable problems. For others, they will have problems at 6dB. The guideline I'd go by:

6-7dB Marginal. Likely to have errors to some degree, may be an indication of a line problem (house wiring or Qwest cable), but might just mean the signal is weak due to distance from the DSLAM.

8-9dB: OK. You'll probably get some occasional errors, but unless there's a problem of some sort, you should have a pretty stable connection... but if your SNR margin drops much further, you might have problems.

10-12dB: Good. Aside from a few errors here and there, you should have a very stable connection.

13dB and up: Very good. Contrary to the prevailing "more SNR = better" attitude around here, there's really little or no advantage to having an SNR of 30dB compared to 13dB for a given speed unless "bragging rights" counts.

Attenuation- In basic terms, it represents the amount of signal resistance on your line between the modem and DSLAM. The higher the attenuation is, the lower the SNR margin will typically be. Longer/thinner cable is the most common reason for increased attenuation, with line trouble a distant second. Once you get into the high 50's or low 60's, you're approaching the limit.

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by AthlGrond
last modified: 2006-01-03 12:19:50