Command Manual – QoS/ACL 
Quidway S8500 Series Routing Switches  Chapter 2  QoS Commands
 
Huawei Technologies Proprietary 
2-16 
In the case of network congestion, the switch drops packets to release system 
resources. And then no packets are put into long-delay queues. The following two drop 
modes are available:  
z  Tail drop mode: different queues (red, yellow and green) are allocated with 
different drop thresholds. When these thresholds are exceeded respectively, 
excessive packets will be dropped. 
z  WRED drop mode: Drop precedence is taken into account in drop action. When 
only min-thresholds of red, yellow and green packets are exceeded, packets 
between min-thresholds and max-thresholds are dropped randomly at a given 
slope. But when max-thresholds of red, yellow and green packets are exceeded, 
all excessive packets will be dropped. 
Example 
# Set the port Ethernet3/1/1 in WRED drop mode; import WRED 0 as the threshold. 
<Quidway> system-view 
System View: return to User View with Ctrl+Z.   
[Quidway]interface Ethernet3/1/1  
[Quidway-Ethernet3/1/1] drop-mode wred 0 
2.1.20  dscp 
Syntax 
dscp  dscp-list : dscp-value exp-value cos-value  local-precedence-value 
drop-precedence 
undo dscp dscp-list 
View 
Conform level view 
Parameter 
dscp-list: Original DSCP value, which can be a single value or several values, in the 
range of 0 to 63. For example, you can type single DSCP value “46”, or DSCP values “0 
8 10 16” (space is required between two values). 
dscp-value: Modified DSCP value, in the range of 0 to 63. 
exp-value: Modified EXP value, in the range of 0 to 7. EXP is MPLS priority of MPLS 
packets. 
cos-value: Modified 802.1p priority value, in the range of 0 to 7 
local-precedence-value: Modified local precedence value, in the range of 0 to 7. 
drop-precedence: Modified drop precedence value, in the range of 0 to 2.