IEEE 802.1p

IEEE 802.1p
The IEEE 802.1p standard defines important methods for traffic class expediting and dynamic
multicast filtering, thus providing QoS at the MAC level. This standard may be considered an
extension to the 802.1Q standard discussed in Chapter 14, “VLANs, Trunks, and VTP.” Three
bits are allocated inside the 802.1Q insert that were unspecified at the time, but have been allocated
by 802.1p.
802.1p establishes eight levels of priority that are conceptually similar to the three bits specified
by IP Precedence. Layer 2 switches can prioritize data in their output buffers according to
these priority bits, and many layer 3 switches are capable of “mapping” the 802.1p Precedence
to the TOS or DiffServe fields inside IP so as to achieve end-to-end QoS across integrated
switched and routed internetworks.