QoS Modes
The QoS mode that is selected applies to all interfaces in the system.
- Basic Mode--Class of Service (CoS).
All traffic of the same class receives the same treatment, which is the single QoS action of determining the egress queue on the egress port, based on the indicated QoS value in the incoming frame. This is the VLAN Priority Tag (VPT) 802.1p value in Layer 2 and the Differentiated Service Code Point (DSCP) value for IPv4 or Traffic Class (TC) value for IPv6 in Layer 3. When operating in Basic Mode, the switch trusts this external assigned QoS value. The external assigned QoS value of a packet determines its traffic class and QoS.
The header field to be trusted is entered in the Global Settings page. For every value of that field, an egress queue is assigned where the frame is sent in the CoS/802.1p to Queue page or the DSCP to Queue page (depending on whether the trust mode is CoS/802.1p or DSCP, respectively).
- Advanced Mode--Per-flow Quality of Service (QoS).
In advanced mode, a per flow QoS consists of a class map and a policer:
- A class map defines the kind of traffic in a flow, and contains one or more ACLs. Packets that match the ACLs belong to the flow.
- A policer applies the configured QoS to a flow. The QoS configuration of a flow may consist of egress queue, the DSCP or CoS/802.1p value, and actions on out of profile (excess) traffic.
- Disable Mode--In this mode all traffic is mapped to a single best effort queue, so that no type of traffic is prioritized over another.
Only a single mode can be active at a time. When the system is configured to work in QoS Advanced mode, settings for QoS Basic mode are not active and vice versa.
When the mode is changed, the following occurs:
- When changing from QoS Advanced mode to any other mode, policy profile definitions and class maps are deleted. ACLs bonded directly to interfaces remain bonded.
- When changing from QoS Basic mode to Advanced mode, the QoS Trust mode configuration in Basic mode is not retained.
- When disabling QoS, the shaper and queue setting (WRR/SP bandwidth setting) are reset to default values.
All other user configurations remain intact.