MPLS Label Switch Router
A Label Switch Router (LSR) is a router found within an MPLS environment. It is also known as a P router or a Provider router. Refer to the following MPLS topology.
The P routers are the devices that composes the core of the MPLS network. They do not connect directly to any customer equipment, but only connect to other P router or to PE routers. Its purpose is to switch packets based on their labels, as well as to remove labels.