Alcatel-Lucent 7750 SR Manual page 1322

VPRN Service Configuration Commands
avg-frame-overhead
Syntax avg-frame-overhead percent
no avg-frame-overhead
Context config>service>vprn>if>sap>egress>queue-override>queue
config>service>vprn>ipsec-if>sap>egress>queue-override>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).
When calculating the frame encapsulation overhead for port scheduling purposes, the system
determines the following values:
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Values max — The max (maximum) keyword 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) keyword 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.
• 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 encapsula-
tion 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 10000 octets and
the avg-frame-overhead equals 10%, the frame encapsulation overhead would be 10000 x 0.1 or
1000 octets.
For egress Ethernet queues, the frame encapsulation overhead is calculated by multiplying the
number of offered-packets for the queue by 20 bytes. If a queue was offered 50 packets then the
frame encapsulation overhead would be 50 x 20 or 1000 octets.
• Frame based offered-load — The frame based offered-load is calculated by adding the offered-
load to the frame encapsulation overhead. If the offered-load is 10000 octets and the encapsula-
tion overhead was 1000 octets, the frame based offered-load would equal 11000 octets.
• Packet to frame factor — The packet to frame factor is calculated by dividing the frame encapsu-
lation overhead by the queue's offered-load (packet based). If the frame encapsulation overhead
is 1000 octets and the offered-load is 10000 octets then the packet to frame factor would be 1000
/ 10000 or 0.1. When in use, the avg-frame-overhead will be the same as the packet to frame fac-
tor making this calculation unnecessary.
7750 SR OS Services Guide