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may discard some low priority packets in case of bandwidth shortage.
If devices of each hop in a network support differentiated service, an end-to-end QoS
solution can be created. QoS configuration is flexible, the complexity or simplicity depends
on the network topology and devices and analysis to incoming/outgoing traffic.
13.1.1.3 Basic QoS Model
The basic QoS consists of five parts: Classification, Policing, Remark, Queuing and
Scheduling, where classification, policing and remark are sequential ingress actions, and
Queuing and Scheduling are QoS egress actions.
Classification: Classify traffic according to packet classification information and generate
internal DSCP value based on the classification information.
Policing and remark: Each packet in classified ingress traffic is assigned an internal
DSCP value and can be policed and remarked.
Policing can be performed based on DSCP value to configure different policies that
allocate bandwidth to classified traffic. If the traffic exceeds the bandwidth set in the policy
(out of profile), the out of profile traffic can be allowed, discarded or remarked. Remarking
uses a new DSCP value of lower priority to replace the original higher level DSCP value in
the packet; this is also called “marking down”.
Queuing and scheduling: Packets at the egress will re-map the internal DSCP value to
CoS value, the queuing operation assigns packets to appropriate queues of priority
according to the CoS value; while the scheduling operation performs packet forwarding
according to the prioritized queue weight.
13.1.2 QoS Configuration
13.1.2.1 QoS Configuration Task Sequence
1． Enable QoS
QoS can be enabled or disabled in Global Mode. QoS must be enabled first in Global
Mode to configure the other QoS commands.
2． Configure class map.
Set up a classification rule according to ACL, VLAN ID, IP Precedence or DSCP to