For questions about Multi-Protocol Label Switching (MPLS), the layer 2.5 protocol used as a transport layer for Traffic Engineering, some Layer 2 & 3 VPN's, and VPLS.
Multi-protocol Label Switching (MPLS) is a type of data-carrying technique for high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links (paths) between distant nodes rather than endpoints. MPLS can encapsulate packets of various network protocols, hence its name "multi-protocol". MPLS supports a range of access technologies, including T1/E1, ATM, Frame Relay, and DSL.