The key indicator of sync quality is your DMT footprint which consists of the following measurements:
| Metric | Upstream (ATU-R) | Downstream (ATU-C) |
| Line Rate Up/Down (bps) | 256,000 | 1,472,000 |
| Attainable Up/Down (bps) | 775,757 | 2,582,456 |
| SNR Margin Up/Down (dB) | 12.5 | 21 |
| Attenuation Up/Down (dB) | 37.5 | 25.5 |
| Output Power Up/Down (dB) | 3.0 | 11.5 |
| CRC Block Length | - | - |
| Interleave Delay (ms) | - | - |
Line Rate: Current sync rate (256Kbps/1472Kbps) - this is the maximum allowed by current FCC tarrifs
Attainable Rate: The sync rate you would obtain if the DSLAM sync limits were removed. This is also a good indicator of the overall quality of the loop. The maximum ADSL sync rate is about 1500Kbps/8000Kbps. If your attainable rate is approaching these values you have a very good/short loop.
SNR (Signal to Noise) Margin: Measures the relative strength of the ADSL signal compared to background noise. Thus, the higher the reading the better. Alcatel specifications indicate that the minimum SNR required to maintain sync is 6dB (decibels).
Attenuation: Measures how much the signal has degraded as it travels from the DSLAM to the modem and vice-versa. In this case, the lower the number, the better. Usually the maximum attenuation that can occur and still have a readable signal is about 60-65dB.
Output Power: Indicates how much power each modem is using. You will see power increase as loop length increases. Additionally, sync frequently becomes unstable when output power is > 15-16dB.
Determine your DMT footprint, as follows::
To verify if your footprint is of the expected quality: