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Figure 7 shows two of the maps (on ingress) that can be used to derive the internal DSCO priority value.
Figure 7. Mapping Priority to Internal DSCP
Maps: Policing Map
Although policing is primarily designed to limit traffic to a set amount of bandwidth, it also has the ability to reduce the priority value of any data
that exceeds the set rate. When this option is configured, the policer uses a map to identify what priority it will mark the data down to.
The map used to perform this task is called the policed-dscp-map. It is a table that contains two columns: the left column is the original priority
value, and the matching value in the column on the right is what value the packet will be marked down to.
Maps: Egress DSCP Mutation
When a packet arrives at a switch port, the trust setting of that port will derive an internal priority value (known as internal DSCP, as described
earlier) that it uses to assign service to the packet while it transits the switch. When the packet is transmitted out a switch port, the actual DSCP
value (written into the IP header) in the outgoing packet is derived from the internal DSCP value. (See Figure 8.)
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