This attribute is a link to the Path component whose parent Sonet or
Sdh component will provide the Aps' working line. It must be
defined.
If the protectionLine is on a card of type 2pOC3SmAtm2 or
2pOC3MmAtm2 the working line must exist under the same Lp as
the protection line, and must link to a Path component under the
same type of port component (Sonet or Sdh) as the protection line.