Provider Backbone Transport
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Provider Backbone Transport (PBT) is a set of enhancements to Ethernet technology that allows use of Ethernet as a carrier class transport network. This uses the concepts of VLAN tagging as per IEEE 802.1Q, Q-in-Q as per IEEE 802.1ad and MAC-in-MAC as per IEEE 802.1ah but disables the concept of flooding/broadcasting and spanning tree protocol. The idea here is to use Ethernet for connection oriented purpose as is the case with present SDH/SONET transport by stripping down the complexity involved with the present Ethernet LAN. It simplifies the operational administration and maintenance (OAM), as in SDH/SONET world, by using additional extensions based on IEEE 802.1ag. It also provide extensions so as to provide path protection levels similar to the UPSR protection in SDH/SONET network.
[edit] Principle of Operation
The packets are forwarded based on outer VLAN ID (VID) and Destination MAC address. The MAC learning function is disabled and the forwarding is based on the cross-connect table updated based on management commands. All broadcast packets are dropped. All Destination Lookup Failure (DLF) packets are dropped rather than broadcasted.
Path protection is provided by using one work and one protect VID. In case of work path failure (as indicated by loss of 802.1ag continuity check (CC) messages) the source node swaps the VID value to redirect the traffic onto the preconfigured protection path within 50 ms.
