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3.1.14.1 QOS CLASSIFICATION
QoS is classified as:
•
Basic QoS - This enables predefined schemes for handling CoS, Drop Precedence Level (DPL), Priority Code Points
(PCP), Drop Eligible Indicator (DEI), Class of Service ID (CoSID), and Differentiated Service Code Points (DSCP):
•
CoS and DPL classification based on PCP and DEI for tagged frames. The mapping table from PCP and DEI to CoS and
DPL is programmable per port.
•
CoS and DPL classification based on DSCP values.
•
DSCP translation.
•
DSCP remarking based on CoS.
•
Per-port CoS and DPL configuration for untagged and non-IP Frames.
•
Per-port CoSID configuration. CoSID is a value that can be used as a selector in Egress Maps and Ethernet Services. It
does not relate to CoS in any way.
•
General classification using an Ingress Map.
•
General remarking using an Egress Map.
•
Advanced QoS - This uses the QoS Control Lists (QCLs), which provides a flexible classification:
•
Higher layer protocol fields (Layer 2 through Layer 4) for rule matching.
•
Actions include reclassification of CoS, DPL, PCP, DEI, DSCP, and ACL policy values. It is also possible to reclassify by
using an Ingress Map.
3.1.14.2 POLICERS
Policers limit the bandwidth of received frames exceeding the configurable rates. Policers can be configured at queue
level or at a port level. There is also a provision to add policers at the EVC level, although this provision is not discussed
in this document.
3.1.14.3 SHAPERS
Egress traffic shaping can be achieved using bandwidth shapers. Shapers can be configured at queue level or at a port
level.
3.1.14.4 SCHEDULING ALGORITHM
Two types of scheduling are possible on the device at a port level:
•
Strict Priority: All queues follow strict priority scheduling.
•
Deficit Weighted Round Robin (DWRR): Scheduling is based on the weights configured for each queue. Configuration
is present to select the number of queues which can be under DWRR. It is possible to include from two to all eight
queues in DWRR mode.
When the number of queues selected for DWRR is less than eight then the lowest priority queues are put in DWRR and
higher priority queues are put in Strict Priority. For example if number of Queues is two for DWRR then Queue 0 and
Queue 1 are set in DWRR mode, and the remaining Queues 2 to 7 are set in Strict Priority.
3.1.14.5 WEIGHTED RANDOM EARLY DETECTION (WRED)
Congestion can be avoided in the queue system by enabling and configuring the Weighted Random Early Detection
(WRED) function. WRED can discard frames with DPL greater than zero.
There are three separate WRED groups, and each port belongs to one of these groups.
Configuration includes enabling WRED per group, queue, and DPL and setting the minimum and maximum Threshold.
Minimum threshold is the queue fills level at which the WRED starts discarding the Frames. Maximum threshold can be
configured as either Drop Probability or Fill Level. When the unit is Drop Probability, the mentioned threshold would be
the Drop Probability with the queue fill level is just about 100%. When the unit is Fill Level, then it represents the queue
fill level where Drop Probability is 100%.
