802.1p priority
802.1p priority lies in the Layer 2 header. It applies to occasions where Layer 3 header analysis is not needed and QoS must be assured at Layer 2.
Figure 26: An Ethernet frame with an 802.1Q tag header
As shown in Figure 26, the 4-byte 802.1Q tag header contains the 2-byte tag protocol identifier (TPID) and the 2-byte tag control information (TCI). The value of the TPID is 0x8100. Figure 27 shows the format of the 802.1Q tag header. The Priority field in the 802.1Q tag header is called 802.1p priority, because its use is defined in IEEE 802.1p. Table 9 shows the values for 802.1p priority.
Figure 27: 802.1Q tag header
Table 9: Description on 802.1p priority
802.1p priority (decimal) | 802.1p priority (binary) | Description |
|---|---|---|
0 | 000 | best-effort |
1 | 001 | background |
2 | 010 | spare |
3 | 011 | excellent-effort |
4 | 100 | controlled-load |
5 | 101 | video |
6 | 110 | voice |
7 | 111 | network-management |