 In the label distribution protocols, this PHP label pop action is advertised as label value 3 « implicit-null» (which is never found in a label, since it means that the label is to be popped).This optimisation is no longer that useful (like for initial rationales for MPLS – easier operations for the routers).Several MPLS services (including end-to-end QoS management, and 6PE) imply to keep a label even between the penultimate and the last MPLS router, with a label disposition always done on the last MPLS router