Spirent SmartBits System, Reference Manual

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Glossary of Terms
Features and Terminology
262 SmartBits System Reference
The first pattern in the sequence for VFD 1 or 2 is a user selectable start value in HEX
called
Start Value . This pattern is entered in the Start Value data box. Up to 6 bytes of
initial data pattern may be entered.
The location of VFD1 in the data pattern of the packet is specified by Offset . Offset is the
number of bits from the beginning of the data packet. For some SmartCards, the offset is
chosen by a number of
bytes .
If a VFD is enabled, it overwrites the background data of the packet at the specified offset
for the length of the VFD.
The only difference in the setup for VFD 2 is the ability to select an offset Adjacent to
VFD1 . This eases setting the two fields in concurrent sections of a frame.
Default offsets for VFD1 & 2 are at the Destination Address and Source Address,
respectively, for Ethernet or TokenRing frames. If the offset is modified, then the area of
the display that states
MAC dest or MAC source is cleared.
Note: The capabilities of VFD1 & 2 differ slightly among the various SmartCard types.
The most notable difference is the capability of a recycle count in the ST-6410, SX-7205
and TR-8405 SmartCards. When enabled, this feature allows the user to enter a value for
the number of times to increment or decrement the VFD. Once this number is reached, the
VFD recycles back to its original start value.
In the Options menu Preferences window, you can select Allow bit level control of VFD1
and VFD2 for 10Mbps Ethernet SC-6x05 SmartCards only. When selected, this option
allows the user to define the length of VFDs 1 and 2 in bits. This feature is similar to
recycling VFD for 100 MB Fast SmartCards. The behavior is not identical to recycling a
VFD. Because consecutive bits are modified on the output stream in network order, if this
feature is used to span a byte boundary, the data will not increment or decrement in a
smooth fashion, but will skip as the high order bits of the next byte change. If Random
VFDs 1 and 2 are selected on a non-byte boundary, behavior will be normal. Default is
Unselected.