Class-based forwarding over RSVP LSPs allows a service packet to be forwarded over a specific RSVP LSP, part of an SDP, based on its ingress determined forwarding class. The LSP selected depends on the operational status and load-balancing algorithms used for ECMP and LAG spraying.
Figure: Class-based forwarding over SDP LSPs illustrates the use of class-based forwarding to direct packets of a service to specific RSVP or static LSPs that are part of the same SDP based on the packets' forwarding class. The forwarding class of the packet is the one assigned to the packet as a result of applying the ingress QoS policy to the service SAP. The VLL service packets are all classified into the ef forwarding class and those that are destined for PE2 are forwarded over LSP1. Multicast and broadcast are classified into the be class and are forwarded over LSP2.
This feature allows service providers to dedicate specific LSPs with a determined level of traffic engineering and protection to select service packets. For example, packets of a VoIP service are assigned the ef class to expedite their forwarding but are also sent over carefully traffic-engineered and FRR-protected LSP paths across the service provider network.