Spirent SmartBits System, Справочное руководство

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Chapter 13: Token Ring Cards
Token Ring Operational Detail
176 SmartBits System Reference
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Limited IEEE-802.5 MAC Protocol Support . With limited support, the card has
been designed primarily as a ring monitor, with the capability to generate high frame
rates and to generate various kinds of error frames and conditions. It will not,
however, function as an Active Monitor. It will not participate in the Token Ring MAC
Claim process, nor will it automatically generate Beacon frames (though it will
generate Beacon frames or other frames on command via SmartLib.
•
The card will respond to ring polls as a Standby Monitor, and it will generate SUA
(stored upstream neighbor address change) frames.
Token Ring Operational Detail
MAC Protocol Support
The TR Smartbits card is not designed to be a formal station on a ring in that it does not
directly participate in MAC protocols such as Neighbor Notification. Its frames are
marked as
bridged on a standard ring analyzer. It is aware of ring protocols and will stop
sourcing frames if it detects ring recovery activity. This behavior is designed to make the
card as unobtrusive as possible and in particular to stop it from aggravating fault
conditions.
Compared to Ethernet frames, Token Ring adapters are less tolerant of randomly formed
frames and so carelessly made up frames may cause ring restarts or even crash other
stations. The Token Ring Smartcard can generate Token Ring specific frame
headers that
are overlaid on the background pattern that make the frames into a form that will co-exist
with other traffic on the ring. This allows users to set up traffic patterns without having to
first specify the basic frame format. This facility is optional and can be switched off or
overlaid with VFDs as needed.
Frame Patterns
This card generates frames based on a background fill pattern overlaid with three variable
field patterns (VFDs). The fill pattern buffer is 2048 bytes long. If the user specifies a
larger frame than this, then the pattern will be repeated. The various VFDs available are as
follows:
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VFD1 . Can be from one to six bytes long placed anywhere in the frame. If the pattern
increments or decrements, then the user can specify an optional repeat count and the
pattern is reset to the start value.
•
VFD2 . Can be from one to six bytes long placed anywhere in the frame. If the pattern
increments or decrements, then the user can specify an optional repeat count and the
pattern is reset to the start value.
•
VFD3 . An arbitrary sequence of bytes that can be placed anywhere in the frame. This
sequence can be specified for a set of one or more frames, the only limitation being