This object selects the frame CoS (class-of-service) policy applied to traffic entering the static encap tunnel, as the description states -- typically either a fixed marking or a mapped marking resolved via a CoS map table. This choice determines whether different customer traffic classes retain distinct QoS treatment as they cross the MPLS core, or instead all get flattened to a single class regardless of how they arrived. For example, choosing a mapped policy lets voice and best-effort traffic entering this tunnel keep separate priority markings across the core, while a fixed policy would collapse them to one uniform marking.