The 7750 SR and 7950 XRS support multiple mechanisms to provide transport tunnels for the forwarding of traffic between PE routers within the 2547bis network.
The 7750 SR and 7950 XRS VPRN implementation supports the use of:
RSVP-TE protocol to create tunnel LSPs between PE routers
LDP protocol to create tunnel LSP's between PE routers
GRE tunnels between PE routers
These transport tunnel mechanisms provide the flexibility of using dynamically created LSPs where the service tunnels are automatically bound (the autobind feature) and the ability to provide specific VPN services with their own transport tunnels by explicitly binding SDPs if needed. When the autobind is used, all services traverse the same LSPs and do not allow alternate tunneling mechanisms (like GRE) or the ability to craft sets of LSPs with bandwidth reservations for specific customers as is available with explicit SDPs for the service.