The type of VLAN encapsulation in use on this private
vlan trunk port.
dot1Q(1) indicates that the port accepts and transmits
packets with IEEE 802.1q VLAN encapsulation
isl(2) indicates that the port accepts and transmits
packets with Inter Switch Link (ISL) VLAN encapsulation
If the cpvlanTrunkPortDynamicStatus is notTrunking(2) or
if the encapsulation type negotiation has not been
completed, the object is set to notApplicable(3).