Dell BigIron RX Series, Configuration Manual

Page: 570 / 1458

494 BigIron RX Series Configuration Guide
53-1002253-01
Scheduling traffic for forwarding
18
Scheduling traffic for forwarding
If the traffic being processed by a
device
is within the capacity of the switch, all traffic is
forwarded as received. Once we reach the point where the switch is bandwidth constrained, it
becomes subject to drop priority if configured as described in
“Determining packet drop priority
using WRED” on page 487 or traffic scheduling as described in this section.
Traffic scheduling allows you to selectively forward traffic according to the forwarding queue that is
mapped to according to one of the following schemes:
•
Strict priority-based scheduling – This scheme guarantees that higher-priority traffic is always
serviced before lower priority traffic. The disadvantage of strict priority-based scheduling is
that lower-priority traffic can be starved of any access.
•
Enhanced strict scheduling – With enhanced strict scheduling enabled, a configurable
minimum bandwidth is allocated to lower-priority traffic so that it is not starved. The remaining
bandwidth is used in a strict scheduling manner.
•
WFQ destination-based scheduling – With WFQ destination-based scheduling enabled, some
weight-based bandwidth is allocated to all queues. With this scheme, the configured weight
distribution is guaranteed across all traffic leaving an egress port.
•
WFQ source-based scheduling – With WFQ source-based scheduling enabled, some
weight-based bandwidth is allocated to all queues. With this scheme, the configured weight
distribution from an input port is guaranteed allocation in relationship to the configured weight
distribution. However, because multiple input ports can aggregate traffic to a single output
port, the traffic egressing a single port may not equal the configured values.
•
Maximum rate-based scheduling – With maximum rate-based scheduling enabled, a
configured maximum bandwidth is allocated to each priority level. Bandwidth remaining after
the aggregate maximum is allocated is not used.
•
Minimum rate-based scheduling – With minimum rate-based scheduling enabled, a configured
minimum bandwidth is allocated to each priority level. Bandwidth remaining after the
aggregate minimum is allocated is redistributed equally among the four priority queues.
Configuring traffic scheduling
Traffic scheduling is configured on a per-port basis. The following sections describe how to
configure each of the traffic scheduling schemes:
•
“Configuring strict priority-based traffic scheduling”
•
“Configuring enhanced strict priority-based traffic scheduling”
•
“Calculating the values for WFQ source and destination-based traffic scheduling”
•
“Configuring WFQ destination-based traffic scheduling”
•
“Configuring WFQ source-based traffic scheduling”
•
“Configuring maximum rate-based traffic scheduling”
•
“Configuring minimum rate-based traffic scheduling”
NOTE
Brocade only support "strict" and "destination-weighted" scheduling schemes. (qos scheduler ..) on
the 16 x 10G modules.