To get back onto subject, apart from the digital modulation twchniques, and the multitude of micro-processors in Modems & DSLAM's, (which my aged analogue brain struggles with), the basic use of audio frequencies & VLF/LF radio frequencies isn't rocket science. RF-wise, two wire(un-screened) usage was always going to be a problem, as opposed to us other lot mainly using Z rated co-ax, for BT & other ISP's. BT & O/R do their best to attain a high S/N Ratio, but externally - anything sparking or producing anything near a sq.wave is a bummer, RFI-wise(theoretically - infinite spectrum). One of the questions I always ask the O/R guys is ' have you seen anything suspicious between us & the exchange'. But their remit just seems limited to using the DMT Tool. In my early HEB Linesman training, and later Electrical Inspector training, we were encouraged to physically observe as much as we could network & installation - wise, as opposed to just using test equipment. I guess my current frustrations with BT & O/R stem from this.
As for record keeping - Jesus, military-wise every action/repair/inspection had to be signed up, then oversigned by an NCO. In the recent D/O fiasco, the poor chap who carried out 12 hrs of work, said that he'd lost at least two hrs due to the wire pair changing done 3 years ago - not being written up in the exchange's log ! In the military, and I expect in the old GPO days, this would've been a serious disiplinary matter.
Regards, David