802.1p priority
802.1p priority lies in the Layer 2 header and applies to occasions where Layer 3 header analysis is not needed and QoS must be assured at Layer 2.
Figure 38: An Ethernet frame with an 802.1Q tag header
As shown in Figure 38, the 4-byte 802.1Q tag header consists of the TPID (2 bytes in length), whose value is 0x8100, and the TCI (2 bytes in length). Figure 39 shows the format of the 802.1Q tag header. The Priority field in the 802.1Q tag header is called the "802.1p priority," because its use is defined in IEEE 802.1p. Table 14 shows the values for 802.1p priority.
Figure 39: 802.1Q tag header
Table 14: 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 |