Users Guide

Class-of-Service 1493
• Simple Random Early Detection (SRED)—Drops packets queued for
transmission on an interface selectively based their drop precedence level.
For each of three drop precedence levels on each SRED-enabled interface
queue, the following parameters can be configured:
– Minimum Threshold: A percentage of the interface queue size below
which no packets of the selected drop precedence level are dropped.
– Drop Probability: When the queue depth exceeds the minimum
thresholds, this value provides a scaling factor for determining the
percentage of congested packets that are dropped.
CoS Queue Usage
CoS queue 7 is reserved by the system and is not assignable. It is generally
recommended that the administrator utilize CoS queues 0 to 3, as CoS
queues 4-6 may be used by the system for other types of system traffic, for
example, routing protocol PDU handling.
Default CoS Values
Table 42-1 shows the global default values for CoS.
NOTE: SRED is only supported on the Dell EMC Networking N1500 Series switch.
Table 42-1. CoS Global Defaults
Parameter Default Value
Trust Mode 802.1p User Priority
802.1p CoS value to queue mapping 802.1p User Priority Queue
0, 3 1
1, 2 0
4, 5 2
6, 7 3