H3C S5500-EI series Operation Manual page 1054

Operation Manual – QoS
H3C S5500-EI Series Ethernet Switches
2) 802.1p precedence
802.1p precedence lies in Layer 2 packet headers and is applicable to occasions where
the Layer 3 packet header does not need analysis but QoS must be assured at Layer 2.
Figure 2-2 An Ethernet frame with an 802.1Q tag header
As shown in the figure above, the 4-byte 802.1Q tag header contains a 2-byte Tag
Protocol Identifier (TPID) whose value is 8100 and a 2-byte Tag Control Information
(TCI). TPID is a new class defined by IEEE to indicate a packet with an 802.1Q tag.
Figure 2-3
Figure 2-3 802.1Q tag headers
In the figure above, the 3-bit priority field in TCI is 802.1p precedence in the range of 0
to 7. In the figure above, the priority field (three bits in length) in TCI is 802.1p
precedence (also known as CoS precedence), which ranges from 0 to 7.
Table 2-3 Description on 802.1p precedence
802.1p precedence
0
1
2
3
4
5
6
7
describes the detailed contents of an 802.1Q tag header.
(decimal)
000
001
010
011
100
101
110
111
802.1p precedence
(binary)
2-4
Chapter 2 Traffic Classification,
TP, and LR Configuration
Description
best-effort
background
spare
excellent-effort
controlled-load
video
voice
network-management