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4 non-zero vpis – Cabletron Systems 9A100 User Manual

Page 57

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SmartSwitch 9A100 User Guide 4-15

Switch Administration

PVC Connections

4.5.4

Non-zero VPIs

The SmartSwitch 9A100 uses 12 bits to define VPI/VCI pairs. The

vccmask

determines how many of the 12 bits are

used for the VPI and how many are used for the VCI. The

vccmask

uses a 2-bit register to hold four different VPI/VCI

12-bit combinations. Table 4-1 shows the registers and the values that come preconfigured on the SmartSwitch 9A100.

Use the

show vccmask

command to view the four preconfigured VPI/VCI combinations.

SmartSwitch # show vccmask

MaskIndex VpiShift VciShift

(In bits) (In bits)

============================================================================

0 0 12

1 2 10

2 4 8

3 6 6

SmartSwitch #

VCCMask combinations dictate what numerical values can be used for VPI/VCI pairs. Any VPI and VCI pairs that fit
the bit distribution of one of the indexed combinations can be used for defining a PVC. If the VPI and VCI values do
not fit one of the indexed combinations, the SmartSwitch 9A100 uses the closest matching indexed combination.

If you need to use values for VPI and VCI that do not fall within the range of one of the preconfigured indexed
combinations, use the

set vccmask

command to replace one of the preconfigured combinations.

For example, change VCCMask indexed combination zero (0) from VPI = 0 bits and VCI = 12 bits to
VPI = 3 bits and VCI = 9 bits.

1.

Use

set vccmask

to change the VPI/VCI values to 3/9.

SmartSwitch # set vccmask

MaskIndex(0) :

VPIShift(0) : 3

VCIShift(12) : 9

SmartSwitch #

2.

Use the

show vccmask

command to see the new VPI/VCI combination.

SmartSwitch # show vccmask

MaskIndex VpiShift VciShift

(In bits) (In bits)

============================================================================

0 3 9

1 2 10

2 4 8

3 6 6

SmartSwitch #

Table 4-1

Values for VPI and VCI

VCC Mask Index

VPI Bits

VPI Values

VCI Bits

VCI Values

0

0

0

12

0 to 4096

1

2

0 to 3

10

0 to 1023

2

4

0 to 15

8

0 to 255

3

6

0 to 63

6

0 to 63