 PBB, PBT, and PBB-TE use an alternative proposed solution, known as MAC-in-MAC, described in the proposed IEEE 802.1ah Provider Backbone Bridges standard, which encapsulates Ethernet frames with a Service Provider MAC header.MAC-in-MAC technology overcomes the inherent scalability limitations of VLAN and Q-in-Q networks that make them impractical for use in larger networks by enabling up to 4000 times as many service instances as supported by traditional VLAN and Q-in-Q networks.In PBB and PBT switches at the edge of the carrier network encapsulate customer traffic within an 802.1ah frame.