"Jim Thompson" wrote in
message ...
On Wed, 09 Feb 2011 07:35:44 -0800, Charlie E.
wrote:

On Wed, 9 Feb 2011 08:39:22 +0000 (UTC), David Lesher
wrote:

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.

IIRC, step didn't reverse the line, but I don't remember the final
stages of the connector that well anymore, so it is possible it did...

Charlie
Former SxS Equipment Maintainer

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

Charlie is correct Jim. Polarity reversal indicated a call was answered.

Perhaps you recall the early days of third party long distance carriers...
The tone pad on the calling phone was often disabled, presumably by the
polarity reversal, which made it impossible to enter the long distance codes
for a third party carrier. Personally, I carried a pocket dialer which
stored
touch tone sequences in a calculator size device. I would hold it to the
phone
transmitter to complete the call.

In the days of fiber optic links, a polarity reversal is ancient history.

Jon





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