tlsPipStpOperProtocol 1.3.6.1.4.1.6527.3.1.2.4.2.40.1.18

The value of tlsPipStpOperProtocol indicates whether 'stp', 'rstp' or 'mstp' is running on this PIP uplink. If the protocol is not enabled on this PIP uplink, the value 'notApplicable' is returned.