End-To-End Qos Solution Using Classification - Cisco Catalyst 2960 series Configuration Manual

Information About QoS

End-to-End QoS Solution Using Classification

All switches and routers that access the Internet rely on the class information to provide the same forwarding
treatment to packets with the same class information and different treatment to packets with different class
information. The class information in the packet can be assigned by end hosts or by switches or routers along
the way, based on a configured policy, detailed examination of the packet, or both. Detailed examination of
the packet is expected to occur closer to the edge of the network, so that the core switches and routers are not
overloaded with this task.
Switches and routers along the path can use the class information to limit the amount of resources allocated
per traffic class. The behavior of an individual device when handling traffic in the Diff-Serv architecture is
called per-hop behavior. If all devices along a path provide a consistent per-hop behavior, you can construct
an end-to-end QoS solution.
Implementing QoS in your network can be a simple task or complex task and depends on the QoS features
offered by your internetworking devices, the traffic types and patterns in your network, and the granularity
of control that you need over incoming and outgoing traffic.
QoS Basic Model
To implement QoS, the switch must distinguish packets or flows from one another (classify), assign a label
to indicate the given quality of service as the packets move through the switch, make the packets comply with
the configured resource usage limits (police and mark), and provide different treatment (queue and schedule)
in all situations where resource contention exists. The switch also needs to ensure that traffic sent from it
meets a specific traffic profile (shape).
Figure 53: QoS Basic Wired Model
Actions at Ingress Port
Actions at the ingress port include classifying traffic, policing, marking, and scheduling:
• Classifying a distinct path for a packet by associating it with a QoS label. The switch maps the CoS or
DSCP in the packet to a QoS label to distinguish one kind of traffic from another. The QoS label that
is generated identifies all future QoS actions to be performed on this packet.
• Policing determines whether a packet is in or out of profile by comparing the rate of the incoming traffic
to the configured policer. The policer limits the bandwidth consumed by a flow of traffic. The result is
passed to the marker.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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