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DES-7200 Configuration Guide Chapter 2 QoS Configuration
2-4
Just like the criteria for non-IP message classifying, the above classifying criteria can
apply on the same port at the same time. In this case, they will take effect according to
the sequence 3, then 2 and then 1.
For the details of the CoS-to-DSCP map and IP-precedence-to-DSCP map, see the
descriptions below.
2.1.2.2 Policing
The Policing action happens after the data classifying is completed. It is used to
constrain the transmission bandwidth occupied by the classified dataflow. The Policing
action will check every message in the classified dataflow. If the message is occupying
more bandwidth as allowed by the police that applies on that dataflow, the message
will be treated specially, either to be discarded or assigned with another DSCP value.
In the QoS processing flow, the Policing action is optional. If no Policing action is
enabled, the DSCP value of messages in the classified dataflow will remain
unchanged, and no message will be discarded before the message is sent for the
Marking action.
2.1.2.3 Marking
After the Classifying and Policing actions, the Marking action will write the QoS
information for the message to ensure the DSCP value of the classified message can
be transferred to the next hop device in the network. Here, the QoS ACLs can be used
to change the QoS information of the message, or the QoS information is reserved in
the Trust mode. For example, the Trust DSCP can be selected to reserve the DSCP
information in the IP packet header.
2.1.2.4 Queuing
The Queuing action is responsible for transferring the messages in the dataflow to an
output queue of the port. The messages in different output queues will have
transmission service policies of different levels and qualities.
Each port has 8 output queues. The two mapping tables DSCP-to-CoS Map and
Cos-to-Queue Map configured on the switch convert the DSCP value of the message
into output queue number so as to determine which output queue to transfer the
messages into.
2.1.2.5 Scheduling
The Scheduling action is the last cycle in the QoS process. After the messages are
transferring into different output queues of the port, the switch works with WRR or
another algorithm to transmit the messages in those 8 queues.