Basic Qos Model - Cisco Catalyst 2950 Software Configuration Manual

Understanding QoS

Basic QoS Model

Figure 29-2
policing, and marking:
Note If you have the SI installed on your switch, only the queueing and scheduling features are available.
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Actions at the egress interface include queueing and scheduling:
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Figure 29-2 Basic QoS Model
Classification
Classifies the packet
based on the ACL.
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
29-4
shows the basic QoS model. Actions at the ingress interface include classifying traffic,
Classifying distinguishes one kind of traffic from another. For more information, see the
"Classification" section on page
Policing determines whether a packet is in or out of profile according to the configured policer, and
the policer limits the bandwidth consumed by a flow of traffic. The result of this determination is
passed to the marker. For more information, see the
Marking evaluates the policer and configuration information for the action to be taken when a packet
is out of profile and decides what to do with the packet (pass through a packet without modification,
mark down the DSCP value in the packet, or drop the packet). For more information, see the
"Policing and Marking" section on page
Queueing evaluates the CoS value and determines which of the four egress queues in which to place
the packet.
Scheduling services the four egress queues based on their configured weighted round robin (WRR)
weights.
Actions at ingress
In profile or
out of profile
Policing
Determines if the
packet is in profile or
out of profile based
on the policer
associated with the
filter.
29-5.
"Policing and Marking" section on page
29-7.
Mark
Based on whether
the packet is in or
out of profile and the
configured
parameters,
determines whether
to pass through,
mark down, or drop
the packet. The
DSCP and CoS are
marked or changed
accordingly.
Chapter 29 Configuring QoS
Actions at egress
Queuing and
scheduling
Based on the CoS,
determines into
which of the egress
queues to place the
packet, then
services the queues
according to the
configured weights.
78-11380-12
29-7.