On the 7705 SAR, H-QoS adds second-tier (or second-level), per-SAP aggregate shapers. As shown in Figure: Access Ingress Scheduling for 4-Priority and 16-Priority SAPs (with Per-SAP Aggregate Shapers), traffic ingresses at an Ethernet SAP and is classified and mapped to up to eight different CoS queues on a per-ingress SAP basis. The aggregate rate CIR and PIR values are then used to shape the traffic. The conforming 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 SAP ends and the aggregate non-conforming loop begins.
The aggregate non-conforming loop schedules the packets out of the eight CoS queues in strict priority manner. SAPs sending traffic to the 4-priority scheduler do not have a second-tier per-SAP aggregate shaper unless traffic arbitration is desired, in which case an aggregate CIR for all the 4-priority SAPs can be configured (see Access Ingress Per-SAP Shapers Arbitration). See Per-SAP Aggregate Shapers (H-QoS) On Gen-2 Hardware for general information.
The aggregate rate limit for the per-SAP aggregate shaper is configured in the service context, using the sap>ingress>agg-rate-limit or sap>egress>agg-rate- limit command.
For per-SAP aggregate shaping on Gen-2 adapter cards, the SAP must be scheduled using a 16-priority scheduler.
The default setting for scheduler-mode is 4-priority on Gen-2 adapter cards and platforms. The user must toggle the scheduling mode to 16-priority for a given SAP before SAP aggregate shaper rates (agg-rate-limit) can be configured. Before changing the scheduling mode, the SAP must be shut down.
The 16-priority scheduler can be used without setting an aggregate rate limit for the SAP, in which case traffic out of the SAP queues are serviced in strict priority order, the conforming traffic prior to the non-conforming traffic. Using 16-priority schedulers without a configured per-SAP aggregate shaper (PIR = maximum and CIR = 0 kb/s) might be preferred over 4-priority mode for the following reasons:
coherent scheduler behavior across SAPs (one scheduler model)
ease of configuration
As indicated in Figure: Access Ingress Scheduling for 4-Priority and 16-Priority SAPs (with Per-SAP Aggregate Shapers), all the traffic leaving from the shaped SAPs must be serviced using 16-priority scheduling mode.
The SAPs without an aggregate rate limit, which are called unshaped SAPs, can be scheduled using either 4-priority or 16-priority mode as one of the following:
unshaped SAPs bound to a 4-priority scheduler
unshaped SAPs bound to a 16-priority scheduler
The arbitration of access ingress traffic leaving the 4-priority and 16-priority schedulers and continuing towards the fabric is described in the following section.