Figure: Port-based scheduling and queuing shows port-based scheduling and queuing enabled on Access-ports on 7210 SAS-Mxp.
When port-scheduler-mode is enabled, traffic sent out of SAPs configured on access ports and hybrid ports, share a set of 8 egress queues which are mapped to the 8 forwarding classes. A per port scheduler (similar to the one available for network port) distributes the available port bandwidth to all the queues configured on the port in two passes with the behavior being similar to the per SAP scheduler (see below for more details).
Per-SAP scheduler is not present in the scheduler hierarchy when port-scheduler-mode is enabled.
The behavior of the Port-based Queuing and Scheduling on Access Ports is as follows:
If enabled, all SAPs on the node/chassis use port-based queuing.
In other words, user has an option to use either SAP-based queue for all SAPs configured on the node or port-based queues for all SAPs configured on the node. A mix and match of some SAPs using port-based queues and some SAPs using SAP-based queues is not supported.
All SAPs on an access port share the 8 egress queues on the port. On Hybrid ports, SAPs use network port queues. In other words, on hybrid port, all the SAPs configured on the port and the network port IP interfaces share the 8 egress queues on the port.
Supports 2 level hierarchical shaping, with Per queue shaper and per port aggregate shaper (ERL).
Each FC/queue of the port can be shaped to configured rates (CIR/PIR). This is used to control the amount of bandwidth allocated to the FC/queue.
FC to queue mapping is system-defined and not user configurable.
The queue number determines the priority of the queue. Priority of the queue is used only when the queues are configured as strict. Queue ‟8” is the highest priority and Queue ‟1” is the lowest priority.
A queue can be defined to operate in strict mode or weighted mode. The queue mode determines the order of scheduling by the port scheduler.
The scheduling behavior is similar to the one supported on SAPs (modified as below):
Each Access Port has a per port scheduler which operates in SP + WDRR mode and an aggregate per port shaper (ERL). The per port scheduler distributes the available bandwidth to the configured strict and weighted queues, using the configured mode and rates, in 2 passes - CIR loop and PIR loop:
The CIR loop distributes the available bandwidth to all the queues is in the following order:
Higher priority strict queues get the bandwidth up to the configured CIR.
Any remaining bandwidth, if available, is distributed among the lower priority strict queues up to the configured CIR.
Any remaining bandwidth, if available, is distributed among the weighted queues (in the CIR loop, weights are not used and therefore the bandwidth is distributed in equal proportion irrespective of weights configured).
The PIR loop distributes the remaining bandwidth (the bandwidth remaining after CIR loop) to all the queues in the following order:
Higher priority strict queues get the bandwidth, up to the configured PIR.
Any remaining bandwidth, if available, is distributed among the lower priority strict queues, up to the configured PIR.
Any remaining bandwidth, if available, is distributed among the weighted queues in proportion to their configured weights.