boB writes:



Way back when, (back to the 70s or 60s), the polarity would reverse
when the called party answered. This was called supervision or
reversal and propagated all the way back through a long distance
connection.

Very much depended on the office involved. Panel & XY, yes; X-bar nope.
I can't recall what step did.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433