Tripp Lite NGI-M05-C1, Руководство пользователя, Страница: 106 / 254

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Priority refers to the IEEE 802.1p standard that allows the service provider to prioritize
traffic based on the class of service (CoS) the customer has paid for. "0" is the lowest
priority level and "7" is the highest.
VID is the VLAN ID. SP VID is the VID for the second or outer (service provider’s) VLAN
tag. CVID is the VID for the first or inner (Customer’s) VLAN tag.
The frame formats for an untagged Ethernet frame; a single-tagged 802.1Q frame
(customer)and a “double-tagged” 802.1Q frame (service provider) are shown as
following.
untagged
frame
DA SA Len or
Etype
Data FCS
single-tagged
frame
DA SA TPID P VID Len or
Etype
Data FCS
double-tagged
frame
DA SA Tunnel
TPID
P VID TPID P VID Len or
Etype
Data FCS
DA: Destination Address
SA: Source Address
Tunnel TPID: Tag Protocol Identifier added on a tunnel port
P: 802.1p priority
VID: VLAN ID
Len or Etype: Length or Ethernet frame type
Data: Frame data
FCS: Frame Check Sequence
VLAN Stacking Port Roles
Each port can have three VLAN stacking “roles”, Normal, Access Port and Tunnel Port.

Select Normal for “regular” (non-VLAN stacking) IEEE 802.1Q frame switching.

Select
Access Port
for ingress ports on the service provider's edge devices. The
incoming frame is treated as "untagged", so a second VLAN tag (outer VLAN tag)
can be added.

Select
Tunnel Port
for egress ports at the edge of the service provider's network. All
VLANs belonging to a customer can be aggregated into a single service provider's
VLAN (using the outer VLAN tag defined by SP VID).
NOTE: In order to have the double tagged frames switching correctly, user has to configure
a service provider’s VLAN (SPVLAN) on the Q-in-Q switch. Then, the double tagged
frames can be switched according to the SP VID. The SPVLAN should include all the
related Tunnel and Access ports. Also, user has to configure the Tunnel posts as tagged
ports and the Access ports as untagged ports.