Alcatel-Lucent 7450 Quality Of Service Manual page 177

Context config>qos>network-queue>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:
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 1,000 octets.
Quality of Service Guide
• 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.
• 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 10,000 octets and the
encapsulation overhead was 1,000 octets, the frame-based offered-load would equal 11,000
octets.
• Packet to frame factor — The packet-to-frame factor is calculated by dividing the frame-
encapsulation overhead by the queue's offered-load (packet based). If the frame-
encapsulation overhead is 1,000 octets and the offered-load is 10,000 octets then the packet
to frame factor would be 1,000 / 10,000 or 0.1. When in use, the avg-frame-overhead will be
the same as the packet to frame factor making this calculation unnecessary.
• Frame-based CIR — The frame-based CIR is calculated by multiplying the packet to frame
factor with the queue's-configured CIR and then adding that result to that CIR. If the queue
CIR is set at 500 octets and the packet to frame factor equals 0.1, the frame-based CIR would
be 500 x 1.1 or 550 octets.
• Frame-based within-cir offered-load — The frame-based within-cir offered-load is the
portion of the frame-based offered-load considered to be within the frame-based CIR. The
frame-based within-cir offered-load is the lesser of the frame-based offered-load and the
frame-based CIR. If the frame-based offered-load equaled 11000 octets and the frame-based
CIR equaled 550 octets, the frame-based within-cir offered-load would be limited to 550
octets. If the frame-based offered-load equaled 450 octets and the frame-based CIR equaled
550 octets, the frame-based within-cir offered-load would equal 450 octets (or the entire
frame-based offered-load).
Network Queue QoS Policies
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