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 27: An Ethernet frame with an 802.1Q tag header
As shown in Figure 27, 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 28 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 11 shows the values for 802.1p priority.
Figure 28: 802.1Q tag header
Table 11: 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 |