Alcatel-Lucent 7750 SR Manual page 1025

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:
7750 SR OS Services 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 encapsu-
lation 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.
• 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).
As a special case, when a queue or associated intermediate scheduler is configured with a CIR-
weight equal to 0, the system automatically sets the queue's frame based within-cir offered-load
to 0, preventing it from receiving bandwidth during the port scheduler's within-cir pass.
• Frame based PIR — The frame based PIR is calculated by multiplying the packet to frame factor
with the queue's configured PIR and then adding the result to that PIR. If the queue PIR is set to
7500 octets and the packet to frame factor equals 0.1, the frame based PIR would be 7500 x 1.1
or 8250 octets.
IES Service Configuration Commands
Page 1025