Quality of Service Guide Service Egress and Ingress QoS Policies
Edition: 01 3HE 11014 AAAC TQZZA 321
The sum of the MBS for all queues on an adapter card can exceed the total amount of
buffering available. Therefore, for a packet arriving at a queue that has not exceeded its MBS
size, it is not guaranteed that a buffer will be available. If a buffer is not available, the packet
will be discarded. RED/WRED slope parameters can be configured to control congestion in
the case where the buffer capacity of the card is becoming exhausted.
Setting proper CBS parameters and controlling CBS oversubscription is one major safeguard
against queue starvation (that is, when a queue does not receive its fair share of buffers).
Another safeguard is to properly set the RED/WRED slope parameters for the needs of
services on this port or channel.
The no form of this command returns the MBS size assigned to the queue to the default
value.
Default 180 (kbytes) (converted to 78 packets when buffer size is 2304 bytes and to 351 packets
when buffer size is 512 bytes)
Parameters size — the size parameter is an integer expression of the maximum number of bytes of
buffering allowed for the queue. A value of 4000 bytes or less causes the queue to
discard all packets. Selecting default returns the MBS to the default value.
Values 0 to 131072000 | default
bytes — specifies that the size entered is in bytes
kilobytes — specifies that the size entered is in kbytes
rate
Syntax rate pir-rate [cir cir-rate]
no rate
Context config>qos>sap-ingress>queue
config>qos>sap-egress>queue
Description This command defines the administrative PIR and the administrative CIR parameters for the
queue. Defining a PIR does not necessarily guarantee that the queue can transmit at the
intended rate. Similarly, defining a CIR does not necessarily guarantee that the queue can
schedule at the intended rate. The actual rate sustained by the queue can be limited by
oversubscription factors or available bandwidth.
The cir keyword defines the rate at which the system prioritizes the queue over other queues
competing for the same bandwidth.
For service ingress, the PIR defines the maximum rate that the queue can transmit packets
towards the fabric. The cir keyword defines the rate that packets are considered in-profile by
the system. In-profile packets are preferentially queued by the system at egress and at
subsequent next hop nodes where the packet can traverse. To be properly handled as in- or
out-of-profile throughout the network, the packets must be marked accordingly for profiling at
each hop.
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