Quanta Cloud Technology QuantaMesh QNOS5, Configuration Manual

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For platforms that support the multistage scheduling architecture, the COS queue feature provides a method
to configure Traffic Class Groups (TCGs) to extend the COS queue management. Multiple COS queues can be
mapped to a single TCG. Each TCG can have a configured minimum guaranteed bandwidth allocation and a
scheduling algorithm similar to the COS queue configuration. The TCG scheduling and bandwidth
enforcement occurs after the COS queue scheduling and bandwidth enforcement is performed. Therefore
all COS queues mapped to the same TCG share the scheduling and bandwidth properties of the TCG.
9.4.1. CoS Queuing Function and Behavior
Like CoS mapping, CoS queuing uses the concept of trusted and untrusted ports. CoS queuing builds on
includes user-configurable settings that affect hardware queue operation.
9.4.1.1. Trusted Port Queue Mappings
A trusted port is one that takes at face value a certain priority designation within arriving packets. Specifically,
a port may be configured to trust one of the following packet fields:

802.1p User Priority

IP Precedence

IP DSCP
Packets arriving at the port ingress are inspected and their trusted field value is used to designate the COS
queue that the packet is placed when forwarded to the appropriate egress port. A mapping table associates
the trusted field value with the desired COS queue.
9.4.1.2. Un-trusted Port Default Priority
Alternatively, a port may be configured as un-trusted, whereby it does not trust any incoming packet priority
designation and uses the port default priority value instead. All packets arriving at the ingress of an un-
trusted port are directed to a specific COS queue on the appropriate egress port(s) in accordance with the
configured default priority of the ingress port. This process is also used for cases where a trusted port
mapping is unable to be honored, such as when a non-IP packet arrives at a port configured to trust the IP
precedence or IP DSCP value.
9.4.1.3. Queue Configuration
Queue configuration involves setting the following hardware port egress queue configuration parameters:

Scheduler type: strict vs. weighted

Minimum guaranteed bandwidth

Maximum allowed bandwidth (i.e. shaping)

Queue management type: tail-drop vs. WRED

Tail drop parameters: threshold

WRED parameters: minimum threshold, maximum threshold, drop probability