Spirent SmartBits System, Reference Manual

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Chapter 13: Token Ring Cards
Token Ring Operational Detail
SmartBits System Reference 179
Transmitting More Than One Frame per Token
Users are able to specify the Number of Frames per Token . The inter-frame gap figure
used when the token is held is not the normal interframe gap but a non token throw gap
figure. This defaults to 16. The user has the option of specifying whether to set the
Intermediate EDEL bit on frames that hold the token. This gap can be varied to the same
extent as the normal gap (up to about a second on a 16MBits/sec ring).
The TR Smartcard will hold a token when instructed without regard for reserved token
priority on circulating frames. This facility is expected to be used in one of two ways:
•
The user will send more than one frame per token with minimal gap between the
frames (and the
Intermediate bit set as appropriate on the frames) to increase the
traffic density on the ring.
•
The user will send more than one frame per token with a large gap between the frames
(and the
Intermediate bit unset) to lock out a port being tested from the ring.
When the gap is small the card firmware will limit the number of frames transmitted per
token to keep the total Token Holding Time to below 10m/Sec.
Introducing Errors into Frames
The TR Smartcard can put one of five hardware errors into frames:
•
FCS errors.
•
Burst5 errors.
•
Setting the Frame Copied bit in FS.
•
Setting the Error bit in EDEL.
•
Setting the FS byte so its meaningless.
Errors are currently specified by type and percentage . Type determines which one of the
five errors will be introduced and percentage determines how often a bad frame will be
placed in the data stream. The current firmware introduces bad frames on a countdown so
the error placement is really one bad frame in
n good ones rather than the smooth
percentage implied by the Smartwindows application. Thus users can specify 100% (one
bad, no good), 50% (one bad, one good), 33% (one bad, two good) and so on. The
accuracy of error placement is determined by the size of frames; for 60-byte frames the
accuracy level is one bad frame in a group of about 300.
The Single Step frame always has the specified error in it. It will even have the error when
the Percentage figure is zero.