Beta Draft Confidential
Configuring ATM Logical Ports on Frame-based Modules
Setting the Number of Valid Bits in VPI/VCI for the B-STDX 9000
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000 1/19/054-5
Setting the Number of Valid Bits in VPI/VCI for the
B-STDX 9000
The Number of Valid Bits setting applies to the VPI and VCI range that you can use
for VCCs (both PVCs and SVCs). The default values of VPI = 4 (4 bits of VPI) and
VCI = 8 (8 bits of VCI) mean that you can use VCCs over the range of VPI = 0 – 15
and a VCI range of VCI = 32 – 255.
The valid range for the number of valid bits in VPI field is 0 – 6; the valid range for the
number of valid bits in VCI field is 6 – 12. You may have to adjust these values in the
following situations:
• In cases where the required VPI/VCI(s) of the attached devices are outside the
default range of VPI = 0 – 15 and VCI = 32 – 255.
• If you use this logical port as a feeder for OPTimum trunks, the VPI value limits
the number of OPTimum trunks you can create on this physical port. The VCI
value limits the number of circuits you can route over each OPTimum trunk.
This OPTimum trunk/circuit trade-off is shown by the following formulas, where
P represents the value in the valid bits in VPI field, and C represents the value in
the valid bits in VCI field:
Maximum virtual paths = 2
P
– 1
Maximum virtual channels = 2
C
– 32
P + C
≤ 12
Keep in mind that the default values and range for this setting are different from
the CBX 500/GX 550 switch. For an overview of VPs and VCs, see page 2-12.
Note – When you configure an OPTimum trunk between two endpoints, the
OPTimum trunk logical ports must match the VPI of the VPC that provides the
connectivity between the two switches. The VPI range for the VPI/VCI valid bits
setting for each endpoint must accommodate this VPI.
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