Shaped SAPs have user-configured rate limits (PIR and CIR)—called the aggregate rate limit—and must use 16-priority scheduling mode. Unshaped SAPs use default rate limits (PIR is maximum and CIR is 0 kb/s) and can use 4-priority or 16-priority scheduling mode.
Shaped 16-priority SAPs are configured with a PIR and a CIR using the agg-rate-limit command in the config>service>service-type service-id>sap context, where service-type is epipe, ipipe, ies, vprn, or vpls (including routed VPLS). The PIR is set using the agg-rate variable and the CIR is set using the cir-rate variable.
Unshaped 4-priority SAPs are considered unshaped by definition of the default PIR and CIR values (PIR is maximum and CIR is 0 kb/s). Therefore, they do not require any configuration other than to be set to 4-priority scheduling mode.
Unshaped 16-priority SAPs are created when 16-priority scheduling mode is selected, when the default PIR is maximum and the default CIR is 0 kb/s, which are same default settings of a 4-priority SAP. The main reason for preferring unshaped SAPs using 16-priority scheduling over unshaped SAPs using 4-priority scheduling is to have a coherent scheduler behavior (one scheduling model) across all SAPs.
In order for unshaped 4-priority SAPs to compete fairly for bandwidth with 16-priority shaped and unshaped SAPs, a single, aggregate CIR for all the 4-priority SAPs can be configured. This aggregate CIR is applied to all the 4-priority SAPs as a group, not to individual SAPs. In addition, the aggregate CIR is configured differently for access ingress and access egress traffic. On the 7705 SAR-8 Shelf V2 and 7705 SAR-18, access ingress is configured in the config>qos>fabric-profile context. On the 7705 SAR-M, 7705 SAR-H, 7705 SAR-Hc, 7705 SAR-A, 7705 SAR-Ax, and 7705 SAR-Wx, access ingress is configured in the config>system>qos>access-ingress-aggregate-rate context. For all platforms, access egress configuration uses the config>port>ethernet context.
For more information about access ingress scheduling and traffic arbitration from the 16-priority and 4-priority schedulers toward the fabric, see Access Ingress Per-SAP Aggregate Shapers (Access Ingress H-QoS).
