3Com S7906E Configuration Manual page 1623

UPE
User facing provider edge device that functions as the user access convergence device.
NPE
Network provider edge device that functions as the network core PE. An NPE resides at the edge of a
VPLS network core domain and provides transparent VPLS transport services between core networks.
VSI
Virtual switch instance that maps actual VPLS access links to virtual links.
PW
Pseudo wire that is the bidirectional virtual connection between VSIs. A PW consists of two
unidirectional MPLS virtual circuits (VCs).
AC
Attachment circuit that connects the CE to the PE. It can use physical interfaces or virtual interfaces.
Usually, all user packets on an AC, including Layer 2 and Layer 3 protocol messages, must be
forwarded to the peer site without being changed.
QinQ
802.1Q in 802.1Q, a tunneling protocol based on 802.1Q. It offers a point-to-multipoint L2VPN service
mechanism. With QinQ, the private network VLAN tags of packets are encapsulated into the public
network VLAN tags, allowing packets to be transmitted with two layers of tags across the service
provider network. This provides a simpler Layer 2 VPN tunneling service.
Forwarders
A forwarder functions as the VPLS forwarding table. Once a PE receives a packet from an AC, the
forwarder selects a PW for forwarding the packet.
Tunnel
A tunnel, usually an MPLS tunnel, is a direct channel between a local PE and the peer PE for
transparent data transmission in-between. It is used to carry PWs. A tunnel can carry multiple PWs.
Encapsulation
Packets transmitted over a PW use the standard PW encapsulation formats and technologies: Ethernet
and VLAN.
PW signaling
The PW signaling protocol is the fundament of VPLS. It is used for creating and maintaining PWs and
automatically discovering VSI peer PE. Currently, there are two PW signaling protocols: LDP and BGP.
Figure 1-1 shows a typical VPLS networking scenario.
1-2