xtent. The demarcation between the customer and the provider enables enhanced security as switches are not exposed to un-trusted MAC addresses. At the same time, PBB had the effect of radically reducing the number of different MAC addresses known by core bridges, providing for a substantially enlarged service tag field and putting the operator Transmission Networks fully in control of all information on which core bridges switched while simultaneously eliminating any requirement for core bridges to examine or otherwise act on the customer MAC [34]. IEEE 802.1Qay (PBB-TE) PBB-TE is standardized as IEEE 802.1Qay [35] and has emerged from PB and PBB standards. It makes use of both stacked VLANs and MAC-in-MAC, but with some distinction. The distinction is that flooding and broadcasting mechanisms and Spanning Tree Protocols (STP) are not used, that is, they are switched off by default. This allows creating manual end-to-end connection oriented Ethernet paths with predictable bandwidth and delay. A second innovation in PBB-TE is in addressing. While use of global VLAN tags implies that the address space is limited, using MAC addresses to identify source-destination pairs simply is not safe from a provider's perspective. What PBB-TE does is take the combination of a VLAN tag along with the globally unique MAC address, leading to a 60-bit (12+48) unique address. This address need not be learned but can be applied to switches in order to create an end-to-end Ethernet circuit, with all the OAMP features that one might expect in a carrier-class service. The 60-bit address is now used to identify the Ethernet path (towards the destination). PBB-TE is a profile of Ethernet behavior whereby provider MAC bridge tables are configured instead of learned. PBB put operators in control of which endpoint identifiers appear in switching tables, and PBB-TE focuses on how those switching tables are used. In that regard it is a comparatively small change to the Ethernet data plane whereby the normal procedure of flooding of frames for 