Jim Thompson writes:


I always thought that line-reversal (or applying a voltage) was used
to hang up a call you didn't originate.

Nope. That's been automagic for years. Hang up for X seconds.
Step may not have had it; XB surely did. It came into being
because the Jesse James Gang's successors would call all the
bank's numbers, locking them up, THEN rob the place.

What's going away/gone is CPC; Calling Party Control. It
momentarily dropped loop current on the CALLED line when the
caller hung it.

It was there to handle the abandoned call, where you called
Microsoft Support and were put on hold for 2 years; or Bell
Repair, for that matter. It came into being with the 1A key
system "HOLD" feature, but also helped on answering machines.

But that's almost all gone; many remotes (SLC-types) have no way
to interrupt the loop current. Amazingly, the ARRIS ATA's used
by ComCrap and other cable carriers do seem to have it.


--
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