Description
The idea of PBB is to offer complete separation of customer and provider domains. For this purpose, a new Ethernet header has been defined. This header may take multiple different forms, but the main components of the header are:
- Backbone component, that has:
- Backbone destination address (B-DA) (six bytes)
- Backbone source address (B-SA) (six bytes)
- EtherType 0x88A8 (two bytes)
- B-TAG/B-VID (two bytes), this is the backbone VLAN indicator
- Service encapsulation, that has:
- EtherType 0x88E7 (two bytes)
- Flags that contain priority, Drop Eligible Indicator (DEI) and No Customer Address (NCA) indication (e.g. OAM frames).
- I-SID, the service identifier (three bytes)
- Original customer frame
- Customer destination address (six bytes)
- Customer source address (six bytes)
- EtherType 0x8100 (two bytes)
- Customer VLAN identifier (two bytes)
- EtherType (e.g. 0x0800)
- Customer payload
PBB defines a 48 bit B-DA and 48 bit B-SA to indicate the backbone source and destination MAC addresses. It also defines a 12 bit B-VID (backbone VLAN ID) and 24 bit I-SID (Service Instance VLAN ID). The bridges in the PBB domain switch based on the B-VID and B-DA values, which contain 60 bits total. Bridges learn based on the B-SA and ingress port value and hence is completely unaware of the customer MAC addresses. I-SID allows to distinguish the services within a PBB domain.
PBB is the foundation for the IEEE 802.1Qay PBB-TE standard, which was standardized in 2009.
PBB is sometimes referred to as Mac-in-Mac.
Read more about this topic: IEEE 802.1ah-2008
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