This read-create INTEGER sets the desired VLAN trunk encapsulation, such as ISL, 802.10, LANE, or dot1Q, for a specific trunk port, or negotiate to let the encapsulation be determined dynamically, though negotiate isn't allowed if the port's dynamic trunking state is forced to on or onNoNegotiate. An administrator sets this explicitly when a trunk needs to match a specific encapsulation required by the far-end device, rather than relying on negotiation. For example, connecting to older equipment that only understands ISL would require setting vlanTrunkPortEncapsulationType to isl(1) instead of leaving it to negotiate.