Having recently moved from the well controlled environment of coaxial cable provided by VM to the rather more variable nature of the copper pair, I was wondering how OR recognise and correctly connect the balance pairs?
I've had been with VM (Nynex -> NTL->VM) for 20 years before being pushed over the edge to end up in VDSL land.
Like anybody contemplating moving to the relatively unknown (and unsafe) environment of the twisted pair, I decided to take a look at my own (twenty year old) 'wet string'.
Having a look inside my BT66 box (where my cable operator 20 years previous had taken great pleasure in cutting wires to my mater socket), I noticed that the old BT cable, coming in from an underground conduit, had ten cables. I also noticed that five of these were colour coded and the remain five were all white.
Luckily, these five pairs were connected to a (rather corroded) screw terminal so took the opportunity to twist the colour/white pairs and disconnect and check for conductor metal type.
In twisting these pairs I started thinking about how OR (or twenty+ years ago, BT) knew which white wire was paired with each colour.
As it's rather important to maintain an impedance balance between the pairs to reduce cross talk and noise induction, how do OR ensure the correct white/colour pair is maintained?