Line turnaround?

[Little.Fleas%hi-multics at sri-unix.UUCP]

From:      Gary Little <Little.Fleas at hi-multics>

Allmost, but not quite.  Think of line turn around as "one way
reversible".  Either party may transmit, but not at the same time.  Take
2 Amateur radio operators using FM on a frequency of about 146 mhz (2
meters).  When operator A is talking, his radio is locked in the
transmit mode with the receiver disabled (there is either a mechanical
or a solid state relay in the radio that senses the tranmitter active
and either electroniclly or physically disconnects the receiver from the
antenna).  In order for A to listen to B, he must unkey his transmitter,
which then causes his receiver to be connected to the antenna, and now
he can hear the dulcit tones of B coming out of his speaker.

Line turn around is the activity that must be performed to take a
communcations line currently in one mode (transmit), to the other mode
(receive) of operation.  This may be performed by either hardware or
software, depending upon the designers budget, or whether or not he hate
software types.  It takes time and usually is not preferred if a full
duplex system is possible (transmit receive active at same time --
you can hear him while you are talking).  However, you do see it used in
some bi-synchronous modems.