Huawei Quidway S5600 Series Operation Manual page 716

Operation Manual - QoS&QoS Profile
Quidway S5600 Series Ethernet Switches
Figure 1-2 An Ethernet frame with a 802.1Q tag header
As shown in the figure above, each host supporting 802.1Q protocol adds a 4-bit
802.1Q tag header after the source address of the former Ethernet frame header when
sending packets.
The 4-bit 802.1Q tag header contains a 2-bit Tag Protocol Identifier (TPID) whose value
is 8100 and a 2-bit Tag Control Information (TCI). TPID is a new class defined by IEEE
to indicate a packet with an 802.1Q tag. Figure 1-3 describes the detailed contents of
an 802.1Q tag header.
Figure 1-3 802.1Q tag headers
In the figure above, the 3-bit priority field in TCI is 802.1p priority in the range of 0 to
7.The 3 bits specify the precedence of the frame.8 classes of precedence are used to
determine which packet is sent preferentially when the switch is congested.
Table 1-3 Description on 802.1p priority
CoS (decimal)
0
1
2
3
4
5
6
7
The precedence is called 802.1p priority because the related applications of this
precedence are defined in detail in the 802.1p specification.
CoS (binary)
000
001
010
011
100
101
110
111
Huawei Technologies Proprietary
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Chapter 1 QoS Configuration
Description
best-effort
background
spare
excellent-effort
controlled-load
video
voice
network-management