H3C S5120-EI Series, Руководство по эксплуатации

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10-5
802.1p Priority
802.1p priority lies in Layer 2 packet headers and is applicable to occasions where Layer 3 header
analysis is not needed and QoS must be assured at Layer 2.
Figure 10-2
An Ethernet frame with an 802.1Q tag header
As shown in
Figure 10-2 , the 4-byte 802.1Q tag header consists of the tag protocol identifier (TPID, two
bytes in length), whose value is 0x8100, and the tag control information (TCI, two bytes in length).
Figure 10-3 presents 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 10-6 presents the values for
802.1p priority.
Figure 10-3
802.1Q tag header
1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 Priority VLAN ID
TPID (Tag protocol identifier) TCI (Tag control information)
Byte 1 Byte 2
0
Byte 3 Byte 4
CFI
7 5 4 3 2 1 0 7 5 4 3 2 1 0 6 6 7 5 4 3 2 1 0 7 5 4 3 2 1 0 6 6
Table 10-6
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