IEEE 802.1p Priority Levels
IEEE 802.1p was specified by an IEEE 802.1 Task Group to address traffic prioritization for Quality of Service (QoS). 802.1p is not a separate IEEE 802.1 standard, but is defined in Annex G of the IEEE 802.1Q-2005 standard.
IEEE 802.1p defines a 3-bit field called the Priority Code Point (PCP) within an IEEE 802.1Q tag. For NDIS packets, the 802.1p PCP value is specified by the UserPriority member of the NDIS_NET_BUFFER_LIST_8021Q_INFO structure that is associated with a packet's NET_BUFFER_LIST structure.
The PCP value defines 8 priority levels, with 7 the highest priority and 1 the lowest priority. The priority level of 0 is the default. Each priority level defines a class of service that identifies separate traffic classes of transmitted packets.