Specifications

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To define limits to bandwidth utilization on a point-to-point interface or to limit
buffer use, you need to include the shaping statement. For point-to-point
interfaces, include the shaping statement at the [edit interfaces interface-name
unit logical-unit-number] hierarchy level:
[edit interfaces interface-name]
user@host# show
unit logical-unit-number {
vci vpi-identifier.vci-identifier;
shaping {
vbr peak rate sustained rate burst length;
queue-length number;
}
}
For virtual circuits that are part of a point-to-multipoint interface, include the
shaping statement at the [edit interfaces interface-name unit logical-unit-number
family family address address] hierarchy level:
[edit interfaces interface-name unit logical-unit-
number family family]
user@host# show
address address {
multipoint-destination destination-address {
vci vpi-identifier.vci-identifier;
shaping {
vbr peak rate sustained rate burst length;
queue-length number;
}
}
}
To define variable bandwidth utilization, include the vbr statement:
vbr peak rate sustained rate burst length;
You can define the following properties:
Peak rate--Top rate at which bursty traffic can burst
Sustained rate--Normal traffic rate averaged over time
Burst length--Maximum number of cells that a burst of
traffic can contain
Buffers are shared among all VCs, and by default, there is no limit to the buffer
size for a VC. If a VC is particularly slow, it might use all the buffer resources. To
limit the queue size of a particular VC, include the queue-length statement when
configuring the VC:
queue-length number;
The length can be a number from 1 through 16383 packets. The default is 16383
packets.
VBR Finer grained Shaping
JUNOS supports granular increments for ATM Traffic Shaping. The previous SAR
implementation had coarse shaping algorithms, which only allowed speeds which
evenly divide into the full line rate. This meant that you could only shape at 1/2,
1/3, 1/4, ... of the line rate. At higher speeds, the step size is very large. For
example, with OC-12, you go from 271mb/s to 180mb/s, which are 1/2 and 1/3
the line rate respectively.
The Fine Grain Shaping feature creates 128 steps between the existing rates.
This means that there are now 128 values between 1/2 and 1/3, and between 1/3
and 1/4, and so on of the line rate that you can shape to. Thus the rate divisor
will be the integer result of :
((line_rate*128)/desired_rate)/128'