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Overview
Overview
The system creates a port scheduler for all the ports (both access ports and network ports) in the
system and distributes the available bandwidth to all the queues using that port to send out packets.
The port scheduler works either at line-rate or configured egress rate. The port scheduler allocates
bandwidth to the SAPs configured on the access port or to the queues configured on the network
port.
The system creates a SAP scheduler for all the SAPs in the system. It distributes the available port
bandwidth to all the queues allocated to a SAP. The SAP scheduler allocates bandwidth to the
queues based on the configured CIR, PIR rates and the priority and weight assigned to the queues.
Note: The SAP aggregate rate can be configured for the SAP scheduler when SAP based shaping
is in use. For more information, refer to the section on
Listed below are the two passes made by the port scheduler:
•
•
In the belowCIR pass, the port scheduler distributes the available port bandwidth among all the
queues created on the port based on the configured cir-level, until the configured CIR rate is met.
Queues with higher cir-level are scheduled first. The system services queues with CIR-Level "8"
prior to servicing other queues in the system.
Note: To ensure that all the queues in the system are serviced by the scheduler, the queues with cir-
level "8" must be capped to a pre-determinate rate.
In the aboveCIR pass, the port scheduler distributes the remaining port bandwidth among all the
queues based on its pir-level and pir-weight. The pir-level determines the priority of the queue in
the aboveCIR pass. The pir-weight determines the proportion of bandwidth available for the
queue when competing for bandwidth with other queues at the same level.
The pir-level assigned by the system is given in
Table 39: pir-level Assignments
CIR Level Config-
ured for use in CIR
8(highest)
7
6
Page 354
belowCIR pass
aboveCIR pass
PIR level assigned
by system for use
loop
N/A
4
3
7210 SAS-X and 7210 SAS-R6 OS Quality of Service Guide
Table
in PIR loop
Scheduling on page
356.
39:
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