3com 3CDSG8 User Guide
62
QoS
Note: Only one QoS mode can be active at one time. It is not possible, for example, to prioritise
traffic using the DSCP and 802.1p
traffic using the DSCP and 802.1p
There are three main buttons associated with this page:
• HELP - Displays this window.
• APPLY - Saves the settings to memory, and updates the configuration. No changes are
• APPLY - Saves the settings to memory, and updates the configuration. No changes are
made to the switch's configuration until this button is pressed.
• REFRESH - Reloads the current page with the latest configuration setting.
11.1.1
802.1p
The 802.1p field is held within the VLAN-tag of a packet. The field is three bits long so can hold
eight values; 0 - 7 inclusive. When QoS Mode is set to 802.1p, the 802.1p Configuration
table appears which allows a priority to be set for each of the eight values.
eight values; 0 - 7 inclusive. When QoS Mode is set to 802.1p, the 802.1p Configuration
table appears which allows a priority to be set for each of the eight values.
You can use the Prioritize Traffic drop-down list to quickly set the values in the 802.1p
Configuration table. Select All Low Priority to set all values to low priority, All Normal
Priority to set all values to normal priority, All Medium Priority to set all values to medium
priority, or select All High Priority to set all values to high priority. Use Custom if you want to
set each value individually.
Configuration table. Select All Low Priority to set all values to low priority, All Normal
Priority to set all values to normal priority, All Medium Priority to set all values to medium
priority, or select All High Priority to set all values to high priority. Use Custom if you want to
set each value individually.
Note: Because end-stations, like PCs, are not usually VLAN aware, they do not create VLAN-
tagged frames. As a result, this method of prioritization is not ideal when there are a lot of PCs
connected to the Switch.
tagged frames. As a result, this method of prioritization is not ideal when there are a lot of PCs
connected to the Switch.
11.1.2
DSCP
The Differentiated Services Code Point (DSCP) is a six bit field that is contained within an IP (TCP
or UDP) header. Six bits allows the DSCP field to take any value in the range 0 - 63 inclusive.
When QoS Mode is set to DSCP, the DSCP Configuration table appears which allows a
priority to be set for each of the DSCP values.
or UDP) header. Six bits allows the DSCP field to take any value in the range 0 - 63 inclusive.
When QoS Mode is set to DSCP, the DSCP Configuration table appears which allows a
priority to be set for each of the DSCP values.
You can use the Prioritize Traffic drop-down list to quickly set the values in the DSCP
Configuration table. Select All Low Priority to set all values to low priority, All Normal
Priority to set all values to normal priority, All Medium Priority to set all values to medium
priority, or select All High Priority to set all values to high priority. Use Custom if you want to
set each value individually.
Configuration table. Select All Low Priority to set all values to low priority, All Normal
Priority to set all values to normal priority, All Medium Priority to set all values to medium
priority, or select All High Priority to set all values to high priority. Use Custom if you want to
set each value individually.