802.1Q

To ensure interoperability of VLAN technologies from the various network-equipments vendors, the Institute of Electrical and Electronics Engineers (IEEE) developed the 802.1Q specification in 1998.

The IEEE 802 committee had to change the IEEE 802.3 Ethernet frame format by adding a pair of 2-byte fields, TPID and TCI (which consists of three subfields, PCP, DEI, and VID), resulting in a VLAN-compliant 802.1Q Ethernet frame.

Diagram showing conversion of a 802.3 Ethernet frame to a 802.1Q Ethernet frame by inserting a 802.1Q header between the source address and length fields. The 802.1Q header includes TPID, PCP, DEI, and VID.