VLAN Tag Support VLAN tag support provides another important set of capabilities
that affect service frame delivery and performance. This UNI service attribute allows
Ethernet service frames to be 802.1Q tagged or untagged. They can also be used to
determine how the frames should then be handled, and if tagged, whether the VLAN
ID is used to determine frame delivery.
NOTE UNI pairs for an EVC may support different VLAN tags (one may support it,
the other may not; this is useful in service multiplexing described in the next section).
When VLAN tags at the UNI are supported by the Service Provider, then the subscriber
needs to knows this and also the action??”preserved or discarded or stacked??”if
any, taken by the Service Provider.
Provider Versus Customer VLAN tag A Service Provider may add an additional VLAN
tag to the incoming service frame header to separate from and preserve the customer??™s
VLAN tag, using VLAN stacking (also referred to as Q-in-Q). The MEF has defined the
term Customer Edge VLAN ID (CE-VLAN ID) to represents the customer??™s VLAN ID;
this tag also contains the 802.1p field that the MEF has termed CE-VLAN CoS.
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