IEEE 802.1p is a traffic-handling mechanism to support QoS in local area networks based on IEEE 802 technology, such as Ethernet, token-ring, FDDI and other variations of shared media networks. QoS in LAN networks is of interest because these networks comprise a large percentage of the networks in use in university campuses, corporate campuses and office complexes.
802.1p defines a field in the layer-2 header of 802 packets that can carry one of eight priority values. Typically, hosts or routers sending traffic into a LAN will mark each transmitted packet with the appropriate priority value. LAN devices, such as switches, bridges and hubs, are expected to treat the packets accordingly (by making use of underlying queuing mechanisms). The scope of the 802.1p priority mark is limited to the LAN. Once packets are carried off the LAN, through a layer-3 device, the 802.1p priority is removed.