The Label Switching Router (LSR) is a central component in an MPLS network, Multi-Protocol Label Switching. By means of the label it receives from the Downstream Label Switch Router (LSR), it decides on the assignment of the label to a stream.
Label Switched Routers are used in high performance core networks and process IP data packets. To forward a data packet, label switched routers only analyze the label. They do not analyze the IP header or the data transported in the data packet. When a data packet is received, the LSR router uses the label embedded in the header to determine the next hop in the Label Switched Path( LSP). Before the LSR router forwards the data packet to the next router, it removes the old label from the data packet and replaces it with a new one.