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PBN
A provider bridge network (PBN) connects a PBBN to a customer network. A customer network can
connect to a PBBN directly or through a PBN.
BEB
A backbone edge bridge (BEB) is an edge device in a PBBN. A BEB encapsulates frames from a
customer network by using PBB. It decapsulates PBB frames from a PBBN and forwards them to a
customer network.
BCB
A backbone core bridge (BCB) is a core device in a PBBN. It forwards a PBB frame according to its
B-MAC and B-VLAN. A BCB only forwards frames and learns MAC addresses within the PBBN. It does
not learn a large number of customer MAC addresses. This reduces network deployment costs, and the
PBBN is more expandable.
B-MAC and B-VLAN
A backbone MAC address (B-MAC) is a MAC address associated with a PBB bridge. A backbone VLAN
(B-VLAN) is a VLAN assigned by the service provider for transmitting customer traffic on the PBBN.
For customer frames to be transmitted across a PBBN, the ingress BEB encapsulates them in MAC-in-MAC
format. In the outer frame header, the source MAC address is a B-MAC of the ingress BEB, and the
destination MAC is a B-MAC of the egress BEB. All devices in the PBBN forward the PBB frames based
on the destination B-MAC and B-VLAN.
Uplink port and downlink port
A port that connects a BEB to a PBBN is an uplink port, and a port that connects a BEB to a customer
network is a downlink port. After frames from the customer network are encapsulated in PBB frames, they
are forwarded out of the corresponding uplink ports on the BEB. After PBB frames from the PBBN are
decapsulated, they are forwarded out of the corresponding downlink ports on the BEB according to the
customer MAC addresses.
PBB VSI and I-SID
In a PBBN, a PBB VSI is a virtual switch provided by the service provider, and it is uniquely identified by
a backbone service instance identifier (I-SID). A VSI acts as a virtual switch with all conventional Ethernet
switch functions, including source MAC address learning, MAC address aging, and flooding.
PBB frame format
shows the format of a PBB frame.
Figure 65
PBB frame format