3Com 4210G Series, Configuration Manual, Page: 444 / 1133

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Priority Mapping Configuration
When configuring priority mapping, go to these sections for information you are interested in:
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Priority Mapping Overview
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Priority Mapping Configuration Tasks
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Configuring Priority Mapping
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Displaying and Maintaining Priority Mapping
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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, EXP, 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.
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Local precedence is used for queuing. A local precedence value corresponds to an output queue.
A packet with higher local precedence is assigned to a higher priority output queue to be
preferentially scheduled.
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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.
Priority Mapping Tables
Priority mapping is implemented with priority mapping tables. The device provides various types of
priority mapping tables, or rather, priority mappings. By looking up a priority mapping table, the device
decides which priority value is to assign to a packet for subsequent packet processing.
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dot1p-dp
: 802.1p-to-drop priority mapping table.
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dot1p-lp
: 802.1p-to-local priority mapping table.
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dscp-dot1p
: DSCP-to-802.1p priority mapping table, which is applicable to only IP packets.
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dscp-dp
: DSCP-to-drop priority mapping table, which is applicable to only IP packets.
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dscp-dscp
: DSCP-to-DSCP priority mapping table, which is applicable to only IP packets.