As networks develop rapidly, the time used for end-to-end service convergence if a fault occurs on a carrier's network has been used as an indicator to measure bearer network performance. MPLS TE FRR is one of the commonly used fast switching technologies. The solution is to create an end-to-end TE tunnel between two PEs and a backup label switched path (LSP) that protects a primary LSP. When either of the PEs detects that the primary LSP is unavailable because of a node or link failure, the PE switches the traffic to the backup LSP.
MPLS TE FRR, however, cannot implement fast switching if faults occur on the ingress or egress. If a fault occurs on the ingress or egress, services can only be restored through end-to-end route convergence and LSP convergence. The service convergence time is closely related to the number of routes inside an MPLS VPN and the number of LSP hops on the bearer network. The more VPN routes, the longer the service convergence time.
VPN FRR sets in advance on a remote PE forwarding entries pointing to the active and standby PEs, respectively. In collaboration with fast PE fault detection, VPN FRR can reduce end-to-end service convergence time if a fault occurs on an MPLS VPN where a CE is dual-homed to two PEs. In VPN FRR, service convergence time depends on only the time required to detect remote PE faults and change tunnel status. VPN FRR enables the service convergence time to be irrelevant to the number of VPN routes on the bearer network.
for further details, Please check VPN FRR
