Alcatel-Lucent 7210 SAS Series Quality Of Service Manual page 77

Table 30: Minimum and Maximum Bandwidth Meters Example
Meters
2
1
0
Displayed in
Mbps, whereas the remaining QoS queues have a minimum bandwidth specification of 50 Mbps.
All CoS queues have a maximum bandwidth specification of 1 Gbps. The goal of these settings is
to guarantee the minimum bandwidth settings for each of the queues while also allowing each CoS
queue to fully use the egress port capability by having the maximum bandwidth setting at 1 Gbps.
The strict priority scheduler mode provides low latency service for CoS queues 6 and 7 while their
minimum bandwidth guarantees are being satisfied.
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•
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7210 SAS D, E, K OS Quality of Service Guide
Minimum
50 Mbps
50 Mbps
50 Mbps
Table 30, CoS queues 7 and 6 each have a minimum bandwidth specification of 10
Round robin scheduling across CoS queues — The round robin scheduler mode
provides round robin arbitration across the CoS queues. The scheduler visits each
backlogged CoS queue, servicing a single packet at each queue before moving on to the
next one. The purpose of the round robin scheduler is to provide fair access to the egress
port bandwidth (at a packet level). This works best when packet sizes are approximately
comparable. In this mode, the scheduler services the queues in round-robin for both the
CIR and the PIR loop.
Weighted round robin (WRR) — In WRR mode, the scheduler provides access to each
CoS queue in round robin order.When the scheduler is providing access to a particular
queue, it services a configurable number of back-to-back packets before moving on to the
subsequent CoS queue. A value of strict is used to designate that a particular queue be
considered to be a part of a hybrid Strict + WRR configuration. The values 1 to 15 are
used to indicate the number of back-to-back packets to be serviced when the scheduler is
servicing a particular CoS queue. If the weight specified is N, but if the number of packets
in the queue is lesser than N, the scheduler continues working and moves on to the next
backlogged queue. In this mode, with no strict queues configured, the scheduler services
the queues in round robin in the CIR loop. The configured weights are not considered in
the CIR loop. The weights are used only in the PIR loop.
Weighted deficit round robin (WDRR) scheduling— An inherent limitation of the
WRR mode is that bandwidth is allocated in terms of packets. WRR works well if the
average packet size for each CoS queue flow is known.WDRR aims at addressing this
issue. WDRR provides a bandwidth allocation scheduler mode that takes into account the
variably-sized packet issue by maintaining sufficient state information when arbitrating
across the CoS queues. In this mode, with no strict queues configured, the scheduler
services the queues in round-robin in the CIR loop. The configured weights are not
considered in the CIR loop. The weights are used only in the PIR loop. A weight value of
1 to 15 can be configured for each queue. Based on the weights specified, the respective
amount of bytes is de-queued from the queue. A value of 0 is used to designate that a
Maximum
1 Gbps
1 Gbps
1 Gbps
QoS Policies
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