I wouldn't know about the finer details of physical telecommunications but in this case it would seem the physical (overhead) line that was about 30 metres from

I wouldn't know about the finer details of physical telecommunications but in this case it would seem the physical (overhead) line that was about 30 metres from my property was allowing rainwater to interfere with the signal. That was what was replaced. Voice communication was never a problem (in the assumption I never spoke to people when it rained, I didn't often use the line for voice)