ETH-CFM Service Commands
Page 1028 7750 SR OS Services Guide
The MBS is a mechanism to override the default maximum size for the queue.
The sum of the MBS for all queues on an egress access port can oversubscribe the total amount of
buffering available. When congestion occurs and buffers become scarce, access to buffers is
controlled by the RED slope a packet is associated with. A queue that has not exceeded its MBS size
is not guaranteed that a buffer will be available when needed or that the packet’s RED slope will not
force the discard of the packet. Setting proper CBS parameters and controlling CBS oversubscription
is one major safeguard to queue starvation (when a queue does not receive its fair share of buffers).
Another is properly setting the RED slope parameters for the needs of services on this port or channel.
If the CBS value is larger than the MBS value, an error will occur, preventing the MBS change.
The no form of this command returns the MBS size assigned to the queue.
Default default
Parameters size-in-kbytes — The size parameter is an integer expression of the maximum number of kilobytes of
buffering allowed for the queue.For a value of 100 kbps, enter the value 100. A value of 0 causes
the queue to discard all packets.
Values 0 — 131072 or default
rate
Syntax rate pir-rate [cir cir-rate]
no rate
Context config>service>ies>if>sap>egress>queue-override>queue
config>service>ies>if>sap>ingress>queue-override>queue
config>service>ies>if>sap>egress>sched-override>scheduler
Description This command can be used to override specific attributes of the specified queue’s Peak Information
Rate (PIR) and the Committed Information Rate (CIR) parameters.
The PIR defines the maximum rate that the queue can transmit packets out an egress interface (for
SAP egress queues). Defining a PIR does not necessarily guarantee that the queue can transmit at the
intended rate. The actual rate sustained by the queue can be limited by oversubscription factors or
available egress bandwidth.
The CIR defines the rate at which the system prioritizes the queue over other queues competing for
the same bandwidth. 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.
The CIR can be used by the queue’s parent commands cir-level and cir-weight parameters to define
the amount of bandwidth considered to be committed for the child queue during bandwidth allocation
by the parent scheduler.
The rate command can be executed at any time, altering the PIR and CIR rates for all queues created
through the association of the SAP egress QoS policy with the queue-id.
The no form of the command returns all queues created with the queue-id by association with the
QoS policy to the default PIR and CIR parameters (max, 0).
Default rate max cir 0 — The max default specifies the amount of bandwidth in kilobits per second
(thousand bits per second). The max value is mutually exclusive to the pir-rate value.
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