H3C Technologies H3C SR8800 - Manual (Page 57)

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Configuring priority mapping
Priority mapping overview
When a packet enters a router, the router assigns a set of QoS priority parameters to the packet based
on a certain priority field carried in the packet or the port priority of the incoming port, depending on
your configuration. This process is called priority mapping. During this process, the router may modify
the priority of the packet depending on router status. The set of QoS priority parameters decides the
scheduling priority and forwarding priority of the packet.
Priority mapping is implemented with priority mapping tables and involves priorities such as 802.11e
priority, 802.1p priority, DSCP, EXP, IP precedence, local precedence, and drop precedence.
The local precedence and drop precedence are defined as follows:
• Local precedence is a locally significant precedence that the router assigns to a packet. A local
precedence value corresponds to an output queue. Packets with the highest local precedence are
processed preferentially.
• Drop precedence is a parameter used for packet drop. The value 2 corresponds to red packets, the
value 1 corresponds to yellow packets, and the value 0 corresponds to green packets. Packets with
the highest drop precedence are dropped preferentially.
The router provides the following port priority trust modes:
• Trust packet priority—The router assigns to the packet the priority parameters corresponding to the
packet’s priority from the priority mapping table.
• Trust port priority—The router assigns a priority to a packet by mapping the priority of the receiving
port.
You can select one priority trust mode as needed. Figure 18 shows the process of priority mapping on a
router.
Figure 18 Priority mapping process
The router provides the following types of priority mapping tables
• dscp-dscp: DSCP-to-DSCP priority mapping table, which only applies to IP packets.
• up-dot1p: User-to-802.1p priority mapping table.
• up-dscp: User-to-DSCP priority mapping table.