VLAN Tagging, also known as Frame Tagging, is a method developed by Cisco to help identify packets travelling through trunk links. When an Ethernet frame traverses a trunk link, a special VLAN tag is added to the frame and sent across the trunk link .How does ERS use the VLAN tag?（）

A. for multiple ISDN connections
B. for modem concentrated dial-up connections
C. for a group of users in the same vicinity sharing a connection
D. for use by mobile users

A. Neither broadcast nor multicast traffic is ever flooded in VPLS.
B. Multicast traffic is flooded but broadcast traffic is not flooded in VPLS.
C. VPLS emulates an Ethernet switch, with eachEMS being analogous to a VLAN.
D. Because U-PE devices act as IEEE 802.1 devices, the VPLS core must use STP.
E. When the provider experiences an outage, IP re-routing restores PW connectivity and MAC relearning is needed.

A. bandwidth efficiency
B. cell-switching
C. congestion notification
D. heterogeneous network