H3C Technologies H3C S5120 Series Switches - Manual (Page 355)

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Priority Mapping Configuration
When configuring priority mapping, go to these sections for information you are interested in:
z Priority Mapping Overview
z Priority Mapping Configuration Tasks
z Configuring Priority Mapping
z Displaying and Maintaining Priority Mapping
z Priority Mapping Configuration Examples
Priority Mapping Overview
Introduction to Priority Mapping
The priorities of a packet determine its transmission priority. There are two types of priority: priorities
carried in packets and priorities locally assigned for scheduling only.
The packet-carried priorities include 802.1p priority, DSCP precedence, IP precedence, and so on.
These priorities have global significance and affect the forwarding priority of packets across the
network.
The locally assigned priorities have only local significance. They are assigned by the device for
scheduling only. These priorities include the local precedence and drop precedence, as follows.
z Local precedence is used for queuing. The S5120-SI switches map eight local precedence values
to four output queues as shown in Table 3-1 . For more information about queue scheduling, see
the chapter “Congestion management configuration.”
Table 3-1 Local precedence and queue map
Local precedence Queue ID
0, 1 0
2, 3 1
4, 5 2
6, 7 3
z Drop precedence is used for making packet drop decisions. Packets with the highest drop
precedence are dropped preferentially.
When a packet enters the device from a port, the device assigns a set of QoS priority parameters to the
packet based on a certain priority and sometimes may modify its priority, according to certain rules
depending on device status. This process is called priority mapping. The priority based on which priority
mapping is performed depends on the priority trust mode configured on the port (see section Priority
Trust Mode on a Port . The set of QoS priority parameters decides the scheduling priority and forwarding
priority of the packet.