Service Egress and Ingress QoS Policies
Quality of Service Guide 351
Parameters adaptation-rule — Specifies the adaptation rule to be used while computing the operational CIR
or PIR value.
Values pir — Defines the constraints enforced when adapting the PIR
rate defined within the queue queue-id rate command. The pir
parameter requires a qualifier that defines the constraint used
when deriving the operational PIR for the queue. When the rate
command is not specified, the default applies.
max — The max (maximum) option is mutually exclusive with
the min and closest options. When max is defined, the operational
PIR for the queue will be equal to or less than the administrative
rate specified using the rate command.
min — The min (minimum) option is mutually exclusive with the
max and closest options. When min is defined, the operational
PIR for the queue will be equal to or greater than the
administrative rate specified using the rate command.
closest — The closest parameter is mutually exclusive with the
min and max parameter. When closest is defined, the operational
PIR for the queue will be the rate closest to the rate specified using
the rate command.
avg-frame-overhead
Syntax avg-frame-overhead percent
no avg-frame-overhead
Context config>qos>sap-egress>queue
Description This command configures the average frame overhead to define the average percentage that the offered
load to a queue will expand during the frame encapsulation process before sending traffic on-the-wire.
While the avg-frame-overhead value may be defined on any queue, it is only used by the system for
queues that egress a Sonet or SDH port or channel. Queues operating on egress Ethernet ports
automatically calculate the frame encapsulation overhead based on a 20 byte per packet rule (8 bytes
for preamble and 12 bytes for Inter-Frame Gap). This command applies only to the 7450 ESS and
7750 SR.
When calculating the frame encapsulation overhead for port scheduling purposes, the system
determines the following values:
• Offered-Load — The offered-load of a queue is calculated by starting with the queue depth
in octets, adding the received octets at the queue and subtracting queue discard octets. The
result is the number of octets the queue has available to transmit. This is the packet-based
offered-load.
• Frame-encapsulation overhead — Using the avg-frame-overhead parameter, the frame-
encapsulation overhead is simply the queue’s current offered-load (how much has been
received by the queue) multiplied by the avg-frame-overhead. If a queue had an offered load
of 10,000 octets and the avg-frame-overhead equals 10%, the frame-encapsulation overhead
would be 10,000 x 0.1 or 1,000 octets.
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