This article was previously published under Q222020
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The Institute of Electrical and Electronics Engineering (IEEE) 802.1P signaling method is used for traffic prioritization at OSI Reference Model Layer 2. It is implemented in network adapters and switches for best-effort Quality of Service (QoS). No reservation setup is involved.
The IEEE 802.1P signaling technique is an OSI Layer 2 standard for prioritizing network traffic at the data link/Mac sublayer. It can also be defined as best-effort QoS at Layer 2. 802.1P traffic is simply classified and sent to the destination; no bandwidth reservations are established. 802.1p is a spin-off of the 802.1Q (Vlans) standard. The 802.1Q standard specifies a tag that appends to a Mac frame. The VLAN tag carries VLAN information. The VLAN tag has two parts: The VLAN ID (12-bit) and Prioritization (3-bit). The prioritization field was never defined in the VLAN standard. The 802.1P implementation defines this prioritization field.
802.1P establishes eight levels of priority similar to IP Precedence. Network adapters and switches route traffic based on the priority level. Using Layer 3 switches allows you to map 802.1P prioritization to IP Precedence before forwarding to routers.
Working at Layer 2 allows 802.1P to support IPX, SNA, AppleTalk, and so on.