3Com WX3000 Series Operation Manual page 367

The device does not support marking drop precedence for packets.
A device can operate in one of the following two priority trust modes when assigning precedence to
received packets:
Packet priority trusted mode
Port priority trusted mode
In terms of priority trust mode, the priority mapping process is shown in
Figure 1-4 Assigning precedence to received packets in different trust modes
Trust port priority
Packet
Receiving port
As for packet priority trusted mode, you can configure to trust the following packet priority:
802.1p precedence
DSCP precedence
Trusting the 802.1p precedence
In this mode, you can specify to process the received packets in one of the following two ways.
Keeping the original packet precedence unchanged (the default mode)
Replacing the original packet precedence with the corresponding one (the automap mode).
If a packet does not carry 802.1p precedence, the device uses the priority of the receiving port as the
802.1p precedence of the packet and then looks up the COS-precedence-to-other-precedence
mapping table for the corresponding precedence.
Trusting the DSCP precedence
In this mode, you can specify to process the received packets in one of the following ways.
Keeping the original packet precedence unchanged (the default mode)
Replacing the original packet precedence with the corresponding one (the automap mode)
Looking up the DSCP-precedence-to-DSCP-precedence mapping table for the local DSCP
precedence and then looking up the DSCP-precedence-to-other-precedence mapping table based
on the new DSCP precedence for the one to be assigned to the packets (the remap mode)
N
Y
1-6
Figure
Look up the priority mapping
table based on the packet
priority to assign priority
parameters (including local
precedence and drop
precedence) for the packet
Assign the port priority of the
receiving port to the 802.1p
precedence of the packet and
look up the priority mapping
table based on the packet
priority to assign priority
parameters (including local
precedence and drop
precedence) for the packet
1-4.