Provider Backbone Transport
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Provider Backbone Transport (PBT) aka PBB-TE (defined by IEEE 802.1Qay March 2006) is a set of enhancements to Ethernet technology that allows the 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 (Provider Backbone Bridges (PBB)) 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.
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[edit] Principle of Operation
A service is identified by the I-SID and each service is associated with a PBT trunk. The management system configures the PBT trunks on all the edge and core bridges and each PBT trunk is identified by the B-SA, B-DA and B-VID.
The backbone edge bridges have the special capability to perform the MAC header encapsulation function. The core bridges act as transit nodes. The packets are forwarded based on outer VLAN ID (VID) and Destination MAC address.
The MAC learning function and STP is disabled and the forwarding is based on the static forwarding database (FDB) entries made via 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.
PBT equipment leverages economies of scale inherent in Ethernet promising about 30% - 40% cheaper solutions compared to T-MPLS equipment with identical features and capabilities[1] making PBT a better overall return on investment.[2]
[edit] Key features of PBT
- Traffic engineering & resiliency
- Secure, deterministic delivery
- Service scalability
- Operational simplicity
- Ethernet tunneling w/full MPLS interoperability
- Service and transport layer independence -- the services inside the tunnel could be Ethernet, IP, MPLS pseudo-wires or VPLS
