This read-write enumeration (master(1), slave(2), unknown(3)) is used by the PXM to determine whether this connection endpoint is the master or slave side, with unknown(3) distinguishing the switch module type in an AXIS shelf versus an MGX shelf; in an AXIS shelf a user can still add a channel without specifying slot/port/X-Y-P parameters, but in an MGX shelf the PXM's SPM will reject an addchan request lacking those parameters when frMastership is unknown. An administrator sets this to establish which side of a connection drives setup and teardown decisions, which matters especially during connection provisioning on MGX shelves. For example, adding a channel on an MGX shelf without specifying the X/Y/P parameters while frMastership is left at unknown(3) would cause the PXM's SPM to reject the connection setup request.