Cisco Systems IE 2000 DSCP Maps, Ingress Queue Characteristics

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Cisco IE 2000 Switch Software Configuration Guide
OL-25866-01
Chapter 38 Configuring Standard QoS
Information About Standard QoS
• When VLAN-based QoS is enabled, the switch supports VLAN-based features, such as the VLAN
map.
• You can configure a hierarchical policy map only on the primary VLAN of a private VLAN.
DSCP Maps
For default DSCP mapping, see “Default Mapping Table Settings” section on page 38-8.
DSCP-to-DSCP-Mutation Map
If two QoS domains have different DSCP definitions, use the DSCP-to-DSCP-mutation map to translate
one set of DSCP values to match the definition of another domain. You apply the
DSCP-to-DSCP-mutation map to the receiving port (ingress mu tation) at the boundary of a QoS
administrative domain.
With ingress mutation, the new DSCP value overwrites the one in the packet, and QoS treats the packet
with this new value. The switch sends the packet out the port with the new DSCP value.
You can configure multiple DSCP-to-DSCP-mutation maps on an ingress port. The default
DSCP-to-DSCP-mutation map is a null map, which maps an incoming DSCP value to the same DSCP
value.
Ingress Queue Characteristics
Depending on the complexity of your network and your QoS solution, you might need to perform all of
the tasks in the next sections. You will need to make decisions about these characteristics:
• Which packets are assigned (by DSCP or CoS value) to each queue?
• What drop percentage thresholds apply to each queue, and which CoS or DSCP values map to each
threshold?
• How much of the available buffer space is allocated between the queues?
• How much of the available bandwidth is allocated between the queues?
• Is there traffic (such as voice) that should be given high priority?
Ingress Priority Queue
You should use the priority queue only for traffic that needs to be expedited (for example, voice traffic,
which needs minimum delay and jitter).
The priority queue is guaranteed part of the bandwidth to reduce the delay and jitter under heavy network
traffic on an oversubscribed ring (when there is more traffic than the backplane can carry, and the queues
are full and dropping frames).
SRR services the priority queue for its configured weight as specified by the bandwidth keyword in the
mls qos srr-queue input priority-queue queue-id bandwidth weight global configuration command.
Then, SRR shares the remaining bandwidth with both ingress queues and services them as specified by
the weights configured with the mls qos srr-queue input bandwidth weight1 weight2 global
configuration command.