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Provider Backbone Transport (PBT)

Provider Backbone Transport (PBT) is also known as PBB-TE (defined by IEEE 802.1Qay March 2006). It allows virtual circuits to be built across Carrier Ethernet networks...

PBT builds upon the hierarchical addressing fields created by PBB, but allows Ethernet to operate in a connection-oriented model. And instead of the conventional learning behavior of Ethernet switches, PBT turns off this learning behaviour, and provisions paths across the network using the VLAN ID (VID) as a virtual circuit identifier, similar to other connection-oriented technologies such as Frame Relay and ATM. A consequence of this is that flooding of broadcast, multicast and unknown unicast traffic is also turned off. This removal of flooding makes the network able to scale to the sizes necessary in core networks. In addition, STP is disabled, and instead restoration paths are pre-provisioned by the management systems of the service provider using a suitable control plane, again similar to the MPLS model. The 802.1Qay model is effectively a hybrid technology which can operate as connectionless (like Ethernet), or connection–oriented (like MPLS-TE)

Implementations of PBB-TE allow network nodes to include both conventional PBB and PBB-TE links. Advocates of the technology believe it can compete in the core of carrier networks, in the same way that PBB competes in the access and metro networks.

In early 2007, BT plc added PBB and PBB-TE to the set of technologies which they see as critical to their 21CN initiative. The extent to which Carrier Ethernet will displace MPLS in the distribution and core layers of the network remains to be seen.

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