ZyXEL Communications VES-1616 Support Notes page 36

ZyXEL VES-1616/24FA-5x Series Support Notes
1. Ingress Process:
Each port is capable of passing tagged or untagged frames. Ingress Process
identifies if the incoming frames contain a tag, and classifies the incoming frames
belonging to a VLAN. Each port has its own Ingress rule. If an Ingress rule
accepts tagged frames only, the switch will drop all incoming non-tagged frames
on the port. If an Ingress rule accepts all frame types, the switch allow both
incoming tagged and untagged frames on the port.
When a tagged frame is received on a port, it carries a tag header that has an
explicit VID. Ingress Process directly passes the tagged frame to Forwarding
Process.
An untagged frame does not carry any VID to which it belongs. When an
untagged frame is received, Ingress Process inserts a tag contained the PVID into
the untagged frame. Each physical port has a default VID called PVID (Port VID).
PVID is assigned to untagged frames or priority tagged frames (frames with null (0)
VID) received on this port.
After Ingress Process, all frames have a 4-bytes tag and VID information, and
they are transitioned into Forwarding Process.
2. Forwarding Process:
The Forwarding Process makes forwarding decisions on the received frames
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