NetComm G.SHDSL 4-port Security Modem Routers NB712 - Manual (Page 13)

NB712 / NB714 User Guide 13
YML829 Rev1
as belonging to a particular VLAN based on the value of the VID that is included in the tag header. The presence
of the tag header carrying a non-null VID means that some other device, either the originator of the frame or a
VLAN-aware bridge, has mapped this frame into a VLAN and has inserted the appropriate VID.
The following figure shows the difference between a untagged frame and VLAN tagged frame, where the Tag
Protocol Identifier (TPID) is of 0x8100 and it identifies the frame as a tagged frame. The Tag Control Information
(TCI) consists of the following elements:
1) User priority allows the tagged frame to carry user priority information across bridged LANs in
which individual LAN segments may be unable to signal priority information (e.g., 802.3/Ethernet
segments).
2) The Canonical Format Indicator (CFI) is used to signal the presence or absence of a Routing
Information Field (RIF) field, and, in combination with the Non-canonical Format Indicator (NCFI)
carried in the RIF, to signal the bit order of address information carried in the encapsulated frame.
3) The VID uniquely identifies the VLAN to which the frame belongs.
3.3 Applications
LAN LAN
SHDSL Router SHDSL Router
SHDSL Ethernet Ethernet
LAN
SHDSL Router
SHDSL Ethernet
Internet
DSLAM