QoS and QoS Policies
102
Quality of Service Guide
3HE 11014 AAAC TQZZA Edition: 01
Because the per-VLAN shapers are dual-rate shapers, their aggregate rate CIR and
PIR values shape the traffic, as follows.
• The conforming, in-profile loop (aggregate CIR loop) schedules the packets out
of the eight CoS queues in strict priority manner (queue priority CIRs followed
by queue priority PIRs).
• If the aggregate CIR is crossed at any time during the scheduling operation,
regardless of the per-queue CIR/PIR configuration, then the aggregate
conforming loop for the VLAN ends and the aggregate non-conforming loop
(out-of-profile) begins.
• The aggregate non-conforming loop schedules the packets out of the eight CoS
queues in strict priority manner.
A shaped VLAN configured with default aggregate rate limits (PIR = maximum and
CIR = 0 kb/s) is equivalent to an unshaped VLAN except that its traffic flows through
a per-VLAN shaper rather than getting combined with the bulk (aggregate) of the
unshaped VLANs. Using a shaped VLAN in this way (default rate limits) might be
preferred over using an unshaped VLAN for the following reasons:
• coherent scheduler behavior across VLANs (that is, the use of only one
scheduler model)
• ease of configuration
• higher throughput, as each shaped VLAN gets to transmit one packet at each
pass of the out-of-profile scheduler as opposed to one packet from the
aggregate of unshaped VLAN queues
The arbitration of shaped and unshaped VLAN traffic at the third-tier shaper is
described in the following section.
3.4.6.1 Network Egress Per-VLAN Shapers Arbitration
For shaped VLANs, the configured CIR and PIR limits dictate committed and
uncommitted port bandwidth for each of these VLANs. To ensure that the bulk
(aggregate) of unshaped VLANs can compete for port bandwidth with the aggregate
of CIR rates for the shaped VLANs, the unshaped VLANs (as a group) have their own
aggregate CIR rate, which is configured using the unshaped-if-cir command (under
the config>port> ethernet>network>egress context). Otherwise, without their own
aggregate CIR rate, the unshaped VLANs are only able to send traffic into the port
after the aggregate CIR rates of all the shaped VLANs are serviced. Shaped VLANs
using default aggregate rate limits (PIR = maximum and CIR = 0 kb/s) are serviced
as if they are non-conforming traffic for shaped VLANs.
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