Reference Guide

472 Quality of Service
QoS Modes
A single QoS mode is selected and applies to all interfaces in the system. The
modes are:
• Basic Mode — Class of Service (CoS) .
– Traffic is divided into classes that determine how it is treated. All
traffic in a class is treated with the same QoS action. The QoS action
for the class of traffic determines the egress queue on the egress port,
based on the indicated QoS value in the incoming frame.
The QoS value in the incoming frame is:
•
Layer 2 Packets — VLAN Priority Tag (VPT) 802.1p value
•
Layer 3 IPv4 Frames — Differentiated Service Code Point
(DSCP) value
•
Layer 3 IPv6 Frames —Traffic Class (TC) value
When operating in Basic mode, the switch trusts this
externally-assigned QoS value.
This is the default QoS mode.
•
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 the egress queue, the DSCP or CoS value, and
actions on out-of-profile (excess) traffic.
• Disable Mode (QoS is not enabled)
In this mode, all traffic is mapped to a single best-effort queue, so that no
type of traffic is prioritized over another.