MPLS has got various types of operations that occur while the course of transferring data packets, these are listed below:
Push operation: Push operation is mostly performed by the ingress router, with few exceptions. In push operation label is added to the IP packet or MPLS label stack of the packet.
Swap operation: Swap operation means to swap the top most label by another one before switching the packet to the next downstream LSR. This is mostly done by intermediate LSRs (the one between the edge-LSRs) in the provider network.
POP operation: POP operation is performed by the egress router or by the router preceding it. In POP operation the top most label is removed from the label stack and then prepare the packet for its final destination.
Penultimate hop popping: The process is done by removing the top most label of the MPLS packet. This operation is performed by some LSR in the MPLS network before sending the packet to the Label Edge Router (LER).