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User Guide 66
Configuring QoS Configuring Basic QoS
2
Configuring Basic QoS
Configuration Guidelines
Select the QoS mode according to your network requirements. Three QoS modes are
supported on the switch: Port Based, 802.1P Based and DSCP Based (DSCP/802.1P
Based).
Port Based
The port based QoS mode supports four priority queues, which are labeled as 1 (Lowest),
2(Normal), 3 (Medium) and 4 (Highest).
In this mode, the switch prioritizes packets according to their ingress ports, regardless of
the packet field or type.
802.1P Based
802.1P defines the first three bits in 802.1Q Tag as PRI field. The PRI values are from 0 to7.
The tagged packets are mapped to 4 priority levels based on the PRI value (Lowest=1, 2;
Normal=0, 3; Medium=4, 5; Highest=6, 7).
In this mode, the switch only prioritizes packets with VLAN tag, regardless of the IP header
of the packets.
DSCP/802.1P Based
DSCP priority determines the priority of packets based on the ToS (Type of Service) field
in their IP header. RFC 2474 re-defines the ToS field in the IP packet header as DS field.
The first six bits of the DS field is used to represent DSCP priority. The DSCP values are
from 0 to 63. The IP packets are mapped to 4 priority levels based on the DSCP value
(Lowest=0-15; Normal=16-31; Medium=32-47; Highest=48-63).
In this mode, the switch prioritizes packets with IP header based on DSCP priority first.
Then, the switch prioritizes packets with VLAN tag but without IP header based on the PRI
field. Finally, the switch prioritizes packets without VLAN tag or IP header based on port
priority.
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