I'm struggling to find comprehensive (or at least convincingly accurate) information on what I'm sure must be a FAQ: - What are the "good" values for SNR/attenuation for different line speeds, and more importantly: - what are the symptoms of borderline low SNR? - what are the symptoms of borderline high attenuation? - what (in each case) if the upstream figures are good and downstream bad? - Vice versa? - Regarding CRC errors: - what causes them? - what is a "good reading? (Obviously 0 is good but at what figure should I worry about them?) - what impact do they have? - What impact does hardware play in making up for borderline figures? Eg: - having a crap filter? - having crap cable? - having a crap modem? - having too much or crap telephone equipment hung on the same telephone line? - What does environmental conditions (eg weather) affect: - the SNR and attenuation readings? - the impact of bad values? To put the whole question another way: I want to have a reasonable idea if I visit a customer with ADSL issues, when I look at the information the router can tell me, what I should do. In which cases will changing the hardware help (and in those cases what should I be changing).