I'm currently using an ADSL connection. The SNR-Margin for the Downstream is usually around
6db for a Line-Attenuation of
54db. It's terrible and causes a lot of CRC errors. While, at the same time, the SNR-Margin for the Upstream is usually around
21db for a Line-Attenuation of
38db, and that is very good and almost never causes any CRC errors!
The line service technician told me that there are some high-voltage power cables near the telecommunication equipment cabinet that cause the noise. But, I'm confused:
If the noise is because of the high-voltage power cables, then why the upstream signal is that perfect, while the downstream is that corrupt?!
Please, shed some lights on this. Thank you in advance :)