L2TPv3 - Definition from the Hotspot Shield Glossary
Layer 2 Tunneling Protocol Version three is an pseudo-wire service and is an IEFT standard defined in RFC 3931. Layer 2 Tunneling Protocol Version 3 is an alternative to MPLS (Multiprotocol Label Switching) and is used for data encapsulation at Layer 2 of the OSI reference model.
L2TPv3 is in essence a more efficient and cost effective version of Multiprotocol Label Switching and although some advanced features are lost such as teletraffic engineering, the minimal effort required to implement L2TPv3 and the fact that the features it has lost can be added in the future means that it is a viable alternative and a market favorite. Implementations of L2Tpv3 include Brocade, Clavister, Cisco and ProL2TP.