QoS
SPS208G/SPS224G4/SPS2024 Service Provider Switches User Guide 160
9
Service Types
The following services are available in both Basic and Advanced modes:
• Minimum Delay — The queue is assigned to a Strict Priority policy. To
reduce delay to its optimum, administrators can assign traffic to the highest
priority queue.
• Best Effort — Traffic is assigned to the lowest priority queue. By default, the
device directs best effort packets through queue no. 1 (
q1
).
• WRR Scheduling — Implements Weighted Round Robin (WRR) priority. The
queues are mapped to weight values and bandwidth allocations that
determine the priority of the traffic passing through the queues. The
weights may be assigned to the queues in any order.
Only packets marked with a Forward action are assigned to the output queue,
based on the specified classification. For packets not matched to a policy
classification, Deny is the default action.
The following services are available in Advanced mode:
• Bandwidth Assignments — Maximum and minimum bandwidth thresholds
make sure that the traffic complies with bandwidth availability. The device
discards packets that exceed or are less than the allowed bandwidth range.
• IP DSCP — Packet DSCP tag values are assigned to traffic queues.
• Tail Drop — The tail drop threshold is the length of an output queue which is
considered full. If the tail drop is enabled and the queue is congested, the
device drops packets until the queue reaches the defined tail drop
threshold. Tail drop is configurable only on GE ports.
To optimize the device’s QoS performance, administrators can combine the
various services in the configuration. The QoS profiles can include the following
types of service settings:
• Queue trust mode
• Bandwidth control and maximum/minimum thresholds
• Scheduling
• Traffic shaping on egress interfaces
In Advanced QoS mode, policies can be applied directly to an interface. However,
a policy and ACL cannot be simultaneously applied to an interface.
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