What is considered good DSL line attenuation ?
Line attenuation (loss) is a measure of how much the signal has degraded between the DSLAM and the modem. This is largely a function of the distance from the exchange. The lower the dB, the better for this measurement. Attenuation is logarithmic and each 3dB of attenuation halves the strength of the signal power received.
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
The standard signal attenuation spread for a given speed is somewhere in the region of 15-20dB for ADSL2/2+ speeds and 25-30dB for ADSL1 speeds. The following is a "guesstimate" of the line attenuation and maximum attainable speed based on distance:
Less than 1km = 24Mbit
1.0km = 13.81dB = 23Mbit
1.5km = 20.7dB = 21Mbit
2.0km = 27.6dB = 18Mbit
2.5km = 34.5dB = 13Mbit
3.0km = 41.4dB = 8Mbit
3.5km = 48.3dB = 6Mbit
4.0km = 56dB = 4Mbit
4.5km = 62.1dB = 3Mbit
5.0km = 69dB = 2Mbit
You may also want to try our SG DSL Speed Calculator
Note: ADSL1 and ADSL2 S/N Margins and Attenuation figures may be different despite being delivered from the same DSLAM port over the same copper/filters/etc. to the same modem. This may be due to measurement across only the frequencies actually in use, vs. measurement across all available frequencies.
Below is a detailed table of line attenuation (loss) and the corresponding attainable ADSL/ADSL2+ speeds: