The CIR for a queue performs the following distinct functions:
minimum bandwidth guarantees
The egress queue CIR setting provides the bandwidth for this queue as compared to other queues on the port competing for a share of the available link bandwidth. The queue CIR does not necessarily guarantee bandwidth in all scenarios and also depends on factors such as CIR over-subscription and link port bandwidth capacity. For each packet in an egress queue, the CIR is checked with the current transmission rate of the queue. If the current rate is at or below the CIR threshold, the queue is considered in-profile. If the current rate is above the threshold, the queue is considered out-of-profile. This in and out profile state of queue is linked to scheduler prioritizing behavior as discussed in the following point.
scheduler queue priority metric
The scheduler that serves a group of egress queues prioritizes individual queues based on the current CIR and PIR states. Queues operating below their CIR are always served before those queues operating at or above their CIR. See QoS port scheduler policies for 7210 SAS-T, Schedulers on 7210 SAS-Mxp, and Schedulers on 7210 SAS-R6 and 7210 SAS-R12 for information about scheduler behavior.
Queues at the egress never mark the packets as in-profile or out-profile based on the queue CIR and PIR values. The in-profile and out-profile state of the queue interacts with the scheduler mechanism and provides the minimum and maximum bandwidth guarantees.
When defining the CIR for a queue, the value specified is the administrative CIR for the queue. The user has some control over how the administrative CIR is converted to an operational CIR if the hardware does not support the exact CIR and PIR combination specified. See Adaptation rule for queues for information about the interpretation of the administrative CIR.
Although the 7210 SAS is flexible in how the CIR can be configured, there are conventional ranges for the CIR based on the FC of a queue. A access egress queue associated with the high-priority class normally has the CIR threshold equal to the PIR rate, although the 7210 SAS allows the CIR to be provisioned to any rate below the PIR if this behavior is required.
The CIR for a queue is provisioned in the appropriate queue policy associated with the service object (that is, a network or hybrid port, or an access SAP, as applicable).