In case of an optical interface where the transmitted
and received signals travel on two different strands of
fiber, it is possible that each fiber is patched to a
different interface. For example, the transmit and
receive fibers of this interface may have unidirectional
connections to different optical amplifiers.
This object indicates whether this entry describes a
patch in the receive direction, the transmit direction
or both directions. If both the transmit and receive
fibers of this interface are patched to the same
interface, then this object is set to 'both'. Individual
entries for 'transmit' and 'receive' should not be
created in this case.