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?
provide service internetworking
support transparency for Layer 2 frames
indicate destination as a connection identifier
map to the DLCI in service internetworking
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