CANOGA PERKINS 9145ELB NID Software Version 4.01 User Manual
Page 139
Bandwidth Profiles
9145ELB NID Software User’s Manual
Shapers
129
The double-rate shaping algorithm specifies six parameters:
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CIR: The shaping rate for packets declared Green.
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CBS: The output burst of Green packets.
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CBS*: The maximum burst of Green packets that the queue can accommodate (equiva-
lent to the size of the queue).
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EIR: The shaping rate for packets declared Yellow.
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EBS: The output burst of Yellow packets.
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EBS*: The maximum burst of Yellow packets that the queue can accommodate.
It should be noted that CBS* is greater than or equal to CBS and EBS* is greater than or equal to
EBS. Therefore, the input to the queues can accept a larger burst of traffic than what is output
from the queue (which is the desired behavior for a shaper).
Green and Yellow packets are placed in the queue until the occupancy state exceeds EBS*.
After that point, only Green packets will be allowed into the queue, and all Yellow packets will be
discarded. The transmission scheduling mechanism will continuously transmit frames from the
head of the queue at the CIR without re-coloring them. If the queue occupancy state exceeds
THS (i.e., the queue is almost full by less than one packet of maximum size), then the
transmission scheduling mechanism will transmit the frame at the head of the queue at CIR+EIR,
but it will force its color to Yellow.
There are 19 shapers in the system. They cannot be deleted or created but you can disable or
enable them. An unassigned shaper, that is, a shaper without a profile, is always disabled. In
principle, one shaper is assigned for each Network Port queue; however, several queues can be
assigned to the same shaper.
The 19 shaper entities are created automatically at system startup. By default:
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Shaper 1 is enabled, and assigned to a best effort egress bandwidth profile. Internally, all
queues are assigned to this shaper by default.
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Shaping is disabled for the remaining 18 shapers and the shapers are not assigned.
In order to enable the shaping function, you must associate a shaping bandwidth profile with a
shaper, assign a shaper with a particular entity, and enable the shaping administratively.
Changing the profile associated with a shaper is possible only if the shaping function is disabled.
A shaper can be assigned to:
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The entire Network Port. In this case, the entire egress traffic is shaped according to a
single traffic profile. By default, at system startup, the Network Port is assigned to shaper
1, which in turn has a best effort bandwidth profile associated.
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A single Network Port egress queue, or a group of Network Port egress queues. This
allows you to specify the finest granularity for the traffic shaping. Several queues can be
assigned to the same shaper. It is the responsibility of the user to insure consistency
between the desired shaping outcome and the queue classification configuration.