IEEE standard
In 1996 ,the IEEE 802.1 subcommittee passed a standard called 802.1 Q that define the format for frame tagging. The standard also defines the format to be used in multiswitched backbones and enables the use of multivendor equipment in VLANs. IEEE 802.1 Q has opened the way for further standardization in other issue related to VLANs. Most vendors have already accepted the standard.