An uplink interface type is an interface to services.
A Point-to-Point Protocol over Ethernet connection uses PPPoE to establish the network.
A Point-to-Point Protocol over ATM connection uses PPPoA to establish the network.
A Dual-Stack Lite connection uses DS-Lite through an Address Family Transition Router to establish the network.
A Point-to-Point Protocol over L2TP connection uses PPP and L2TP server to establish the network.