H3C Technologies H3C S12500 Series Switches - Manual (Page 221)

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PBN
As shown in Figure 76 , a network connecting the PBBN with the customer network is a provider bridge
network (PBN). The customer network can connect to the PBBN directly, or through a PBN.
MAC-in-MAC frame
A frame processed by MAC-in-MAC is called a MAC-in-MAC frame. For more information about the
encapsulation format of a MAC-in-MAC frame, see " MAC-in-MAC frame encapsulation ."
BEB
As shown in Figure 76 , a backbone edge bridge (BEB) is an edge device in the PBBN, like a PE device
in an MPLS network. The BEB encapsulates frames from the customer network by using MAC-in-MAC, or
de-encapsulates MAC-in-MAC frames from the PBBN and forwards them to the customer network.
BCB
As shown in Figure 76 , a backbone core bridge (BCB) is a core device in the PBBN, like a P device in an
MPLS network. It forwards MAC-in-MAC frames according to their B-MAC and B-VLAN. A BCB device
only forwards frames and learns MAC addresses in the backbone network. It does not learn a large
number of customer MAC addresses. In this way, the network deployment costs are reduced, and the
PBBN is given better expandability.
B-MAC/B-VLAN
When encapsulating a customer frame, a BEB tags the frame with the service provider MAC address
(known as backbone MAC address, B-MAC) and service provider VLAN (known as backbone VLAN,
B-VLAN). The B-MAC includes source B-MAC and destination B-MAC. In the PBBN, a BCB forwards
MAC-in-MAC frames according to their B-MAC and B-VLAN.
Uplink port/downlink port
The port that connects the BEB to the PBBN is the uplink port, and the port that connects the BEB to the
customer network is the downlink port. After the frames from the customer network are encapsulated in
MAC-in-MAC frames, they are forwarded out of uplink ports on the BEB; after the MAC-in-MAC frames
from the PBBN are de-encapsulated, they are forwarded out of the corresponding downlink port on the
BEB according to the customer MAC.
MAC-in-MAC instance and I-SID
In the PBBN, a MAC-in-MAC instance represents a type of services provided by the service provider, and
is uniquely identified by a backbone service instance identifier (I-SID).
MAC-in-MAC frame encapsulation
Figure 77 Format of a MAC-in-MAC frame