Which transport protocol adds an outer MAC header in MPLS?

The transport protocol that adds an outer MAC header in MPLS is Provider Backbone Bridges Traffic Engineering (PBB-TE). This protocol is designed to enhance the scalability and efficiency of Ethernet networks by allowing for the encapsulation of MAC frames within a backbone infrastructure.

In PBB-TE, the original Ethernet frame is encapsulated within a new MAC header, thereby creating an outer MAC header that enables the transport of the encapsulated frames across the MPLS (Multiprotocol Label Switching) network. This encapsulation allows for the efficient use of the network's bandwidth and supports a large number of VLANs, making it particularly valuable in Provider Backbone Networking environments where large-scale data handling is required.

By leveraging PBB-TE, service providers can better manage the transmission of traffic, enhance traffic engineering capabilities, and reduce the complexity of managing numerous Ethernet frames by providing a more organized structure at the MAC layer while incorporating MPLS functionalities for transport.