Planet Technology G.SHDSL.bis Bridge Router GRT-504 - Manual (Page 23)

GRT-504 4-Wire G.SHDSL.bis Firewall Router User’s Manual
68 octets. Such a frame is classified 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.
4.3 Applications
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