3Com S7906E - Switch, Configuration Manual

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1-6
H-VPLS Implementation
Hierarchy of VPLS (H-VPLS) can extend the VPLS access range of a service provider and reduce
costs.
Advantages of H-VPLS access
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H-VPLS has lower requirements on the multi-tenant unit switch (MTU-s). It has distinct hierarchies
which fulfill definite tasks.
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H-VPLS reduces the logical complexity of the fully meshed network consisting of PEs and the
configuration complexity.
Two H-VPLS access modes
1) H-VPLS LSP access
Figure 1-3 H-VPLS LSP access
As shown in Figure 1-3 , UPE functions as the convergence device MTU-s and establishes only a virtual
link U-PW with NPE 1. It does not establish virtual links with any other peers.
Data forwarding in H-VPLS LSP access mode is as follows:
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Upon receiving a packet from a CE, UPE tags the packet with the MPLS label for the U-PW,
namely the multiplex distinguishing flag, and then sends the packet to NPE 1.
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When receiving the packet, NPE 1 determines which VSI the packet belongs to by the label and,
based on the destination MAC address of the packet, tags the packet with the multiplex
distinguishing flag for the N-PW, and forwards the packet.
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Upon receiving the packet from the N-PW, NPE 1 tags the packet with the multiplex distinguishing
flag for the U-PW and sends the packet to UPE, which forwards the packet to the CE.
For packets to be exchanged between CE 1 and CE 2, UPE can forward them directly without NPE 1
because it holds the bridging function by itself. For the first packet with an unknown destination MAC
address or a broadcast packet, UPE broadcasts the packet to CE 2 through the bridging function and, at
the same time, forwards it through U-PW to NPE 1, which replicates the packet and sends a copy to
each peer CE.
2) H-VPLS QinQ access