GS748T Software User Manual
Configuring the Switch 4-5
v2.0, April 2007
Regulating Traffic Rates using Quality of Service Settings
Quality of Service (QoS) is used to manage traffic in a network by treating different types of traffic
with different levels of priority. Higher priority traffic receives preferential treatment during times
of switch congestion.
Three implementations of QoS are supported:
• Port-based QoS
• IEEE 802.1p-based QoS
• DSCP-based QoS
Port-based QoS
Port-based QoS can be achieved by configuring the Default Priority of a port, as described in
“Port Configuration” on page 4-2.
IEEE 802.1p-based QoS
IEEE 802.1p-based QoS enables the user to map each of the eight priority levels specified in IEEE
802.1p (p0 to p7) to one of four hardware priority queues: High, Normal, Low, and Lowest. The
eight priority levels specified in IEEE 802.1p (p0 to p7) are implemented by a three-bit priority
field in the VLAN tag. The switch empties the four hardware priority queues in order, from High
to Lowest. Packets are transferred to empty the buffers of each higher hardware priority queue in
turn before the next lower hardware priority queue can begin to transfer its received packets
through the switch.
The table in the Quality of Service page below shows an example of IEEE 802.1p-based priority
settings that you can set for a switch.
Figure 4-9