Multiprotocol Label Switching (MPLS) is used by service providers to implement QoS, tag switching, service levels, and many other features. The service is very popular, especially in Europe and Asia. Ethernet over MPLS (EoMPLS) is a Cisco solution that is currently in an RFC draft state with IETF. It extends MPLS by tunneling Layer 2 Ethernet frames across a service provider's Layer 3 core. Doing so provides two advantages:
The service provider has more scalability because it has a Layer 3 core.
Your Layer 2 information, including STP, can be tunneled through the service provider.
Because of these two advantages, service providers prefer EoMPLS over Q-in-Q. EoMPLS, like Q-in-Q, is a tunneling mechanism that tunnels your VLAN ...