3Com Switch 4200G Configuration Guide

222 CHAPTER 27: QOS CONFIGURATION
You can select the priority trust mode of the port as you require.
In the mode of trusting the packet precedence, the switch can trust the following
priorities as you configure:
■ Trust the 802.1p priority of the packets
■ Trust the DSCP precedence of the packets
Trusting the 802.1p
priority of the Packets
You can specify whether to replace the precedence carried in the packet with the
mapped precedence when you configure to trust the 802.1p priority of the packet:
■ In the default mode, the switch does not replace the precedence carried in the
packet with the mapped precedence.
■ In the automap mode, the switch replaces the precedence carried in the packet
with the mapped precedence.
If the packet does not carry any precedence, the switch will perform the
corresponding mapping by using the port precedence to search for the “COS->other
priority mapping table”.
Figure 72 The mapping process of trusting 802.1p priority
Trusting the DSCP
Precedence of the
Packets
You can specify whether to replace the precedence carried in the packet with the
mapped precedence when you configure to trust the DSCP precedence of the packet:
■ In the default mode, the switch does not replace the precedence carried in the
packet with the mapped precedence.
■ In the automap mode, the switch replaces the precedence carried in the packet
with the mapped precedence.
■ In the remap mode, the switch firstly gets new DSCP precedence by the “DSCP-->
DSCP” mapping relationship, and then searches for the “DSCP-->other
precedence” mapping table through the new DSCP precedence and replaces the
precedence carried in the packet with the mapped precedence.
Packets Packets
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
“COS
－
>
other precedence” mapping table
Search for “COS-
according to the COS (802.1p precedence) and
assign other precedence for the packet
Packets Packets
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
>
“COS-
according to the COS (802.1p precedence) and
assign other precedence for the packet
Packets Packets
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
>
Search for “COS-
according to the COS (802.1p precedence) and
assign other precedence for the packet
Packets Packets
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
>
“COS->other precedence” mapping table
according to the COS (802.1p precedence) and
assign other precedence for the packet
Packets Packets
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
“COS
－
>
other precedence” mapping table
Search for “COS-
according to the COS (802.1p precedence) and
assign other precedence for the packet
Packets Packets
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
>
“COS-
according to the COS (802.1p precedence) and
assign other precedence for the packet
Packets Packets
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
>
Search for “COS-
according to the COS (802.1p precedence) and
assign other precedence for the packet
Packets Packets
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
48066
56077
40055
32044
24033
8012
0001
16020
DSCPDropLocal -pre802.1p
>
“COS->other precedence” mapping table
according to the COS (802.1p precedence) and
assign other precedence for the packet