3Com Switch 8800 Advanced Software V5 Configuration Guide

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PRIORITY MAPPING
When configuring traffic classification and traffic shaping, go to these sections for
information you are interested in:
■ “Priority Mapping Overview” on page 851
■ “Configuring a Priority Mapping Table” on page 852
■ “Configuring Port Priority” on page 854
■ “Configuring to Trust Packet Priority” on page 856
Priority Mapping
Overview
When packets enter the switch, the switch allocate a series of parameters
including 802.1p precedence, DSCP, local precedence, and drop precedence to the
packets according to the capability of the switch and the corresponding rules.
The local precedence and drop precedence are defined as follows:
■ Local precedence: locally significant precedence that the switch assigns to the
packets. A local precedence corresponds to an output queue ID.
■ Drop precedence: parameter referenced for packet drop. The drop precedence
for red packets, yellow packets, and green packets is 2, 1, and 0.
Switch 8800s can be configured to trust the packet priority. With packet priority
trust mode configured, the switch looks up the priority mapping table based on
the priority of a packet to assign priority parameters to the packet.
The packet priority mapping process on a Switch 8800 is shown in Figure 250.
Figure 250 Priority mapping process