Resilience of the ATM VC at the gateway PE router is provided via a SONET/SDH link automatic protection switching group. Furthermore, customer STP bridge protocol data units (BPDUs) are transparently passed from the TLS network to the VPLS network. This requires the translation of customer BPDUs from 802.1d format, which operates in the ATM TLS network, to the per-VLAN STP (PVST) format, which is typically used by customer premises equipment that is directly attached to a VPLS PE. This allows each customer to run STP end-to-end to prune the entire topology in order to select an active path and to disable loops.  Resilience is further enhanced on the PEs with technology enhancements such as non-stop routing and non-stop service (NSS) to augment MPLS fast reroute (FRR) on the VPLS network to provide better than sub 50m/s availability.

Conclusion

Enterprises are transitioning from network orientation to application orientation and require an architecture that supports the convergence of sophisticated on-demand video, voice over IP (VoIP) and data applications. The best-effort performance of traditional transparent LAN services becomes insufficient: they do not scale economically, become increasingly difficult to manage, and offer limited support for multiple service classes.   Service providers are seeing the writing on the wall and have already begun to structure their migration to an MPLS-enabled WAN Ethernet solution, such as VPLS.