
Configuring ATM and MPLS Services
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You can change ATM traffic parameters several times before deciding on a
particular set. The following sections describe the traffic parameters and provide
some basic guidelines for customizing them on an ATM PVC or ATM control VC
(that is, the signaling VC or ILMI VC).
Using the PCR
The PCR specifies the upper traffic limit, in cells/second, that the ATM
connection can support.
How you set the PCR depends on:
• The optical transmission rate of your ATM device
• The amount of traffic you expect on a particular VC
• The rate you want for each VC
When setting the PCR, keep the following considerations in mind:
• Each VC can have its own PCR.
• The PCR cannot exceed the maximum rate for the physical media. For
example, you cannot exceed 149.76 Mb/s for an OC-3c line.
• The PCR specifies the desired rate for the attached physical media (that is,
OC-3c, DS-3, or E-3). It does not specify the rate for the ATM network as a
whole. For example, you can specify a full 149.76 Mb/s for each PVC or
control VC on an OC-3c connection. However, if the VC ultimately connects
to a lower-speed link (for example, T1 or E1), your PCR is limited to the
maximum rate for that media.
• ATM VCs may fail to operate with PCR values lower than 128 cells/s.
• The E-3 framing mode setting affects the maximum PCR setting.
Note:
You do not need to manually configure traffic parameters for SVCs (as
you must for PVCs and control VCs), because SVCs dynamically negotiate
these parameters before sending data.
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