QoS
SPS208G/SPS224G4/SPS2024 Service Provider Switches User Guide 158
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The QoS facility involves the following elements:
• Traffic Classification — Classifies each incoming packet as belonging to a
given traffic class, based on the packet contents and/or the context.
• Assignment to Hardware Queues — Assigns incoming packets to
forwarding queues. Packets are sent to a particular queue for handling as a
function of the traffic class to which they belong, as defined by the
classification mechanism.
• Traffic Class-Handling Attributes — Applies QoS/CoS mechanisms to
different classes, including:
- Bandwidth Management
QoS Modes
The device provides the following methods for controlling and configuring CoS/
QoS in the device:
• Basic Mode
• Advanced Mode
The device only works in either one of these modes at a single time, or with QoS
disabled.
During mode change, some configuration settings revert to their default values
Basic QoS Mode
Basic Mode enables users to categorize frames into classes, according to the
ingress interface or a single frame header field value. Each class may be directed
to a specific egress queue. Users can also define Queue priority parameters and
the ports’ bandwidth allocations.
To classify packets, users must apply trust settings which help identify fields for
service assignment. Basic Mode supports the following Trust settings:
• VPT - VLAN Priority Tags are mapped to priority queues.
-
802.1p Tag-based
— The IEEE802.1p tag is used to classify packets. The
packets are mapped, according to the VPT, to an output queue.
Administrators either apply the default VPT mapping (as defined by the
802.1p standard), or may define the mapping according to their own
specifications. Mapping is defined on a device-wide basis.
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