What is penultimate hop popping (PHP) in MPLS?

Penultimate Hop Popping (PHP) is an MPLS optimization where the Label Switching Router (LSR) one hop away from the egress router (the penultimate hop) removes the outermost MPLS label before forwarding the packet to the egress router. This is signaled by the egress router sending an implicit-NULL label (label value 3) to the penultimate hop. This allows the egress router to receive a pure IP packet, eliminating the need for it to perform an MPLS label lookup and then an IP lookup, thus improving its performance. The downstream node (egress router) signals the upstream node (penultimate hop) to perform this action. The option "It uses implicit-NULL for traffic congestion from source to destination forwarding" is incorrect because implicit-NULL is used for label removal, not congestion control. "PE removes the outer label before sending to the P router" is incorrect; PHP involves the penultimate hop removing the label before sending to the egress PE, not a PE removing a label before sending to a P router. "It improves P router performance by not performing multiple label lookup" is incorrect because PHP primarily benefits the egress PE router, not intermediate P routers.