
Configuring Line Services
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The TVX times the period between valid transmissions on the ring. When the
node receives a valid frame or token, the TVX is reset. If the TVX expires, the
node starts a ring initialization sequence to restore the ring to proper operation.
FDDI Ring Maintenance
Each node is responsible for monitoring the integrity of the ring. By using the
TVX, nodes can detect a break in ring activity. If the interval between token
receptions exceeds the value of the TVX, the node reports an error condition and
initiates the claim process to restore ring operation.
If it cannot generate a token, the node that detected the problem initiates beacon
frames. Beacon frames indicate to the other nodes that the ring is broken. If the
beacon transmission exceeds the value set in the stuck beacon timer (controlled by
the Ring Management [RMT] portion of SMT), RMT attempts to restore the ring
to normal operation.
If the ring does not return to normal operation in a specified period of time, RMT
initiates a trace. A trace is a diagnostic function that isolates a fault on the ring.
For more information about RMT, see the next section.
FDDI SMT
Bay Networks routers support Version 7.2 of the SMT protocol. SMT is a
low-level protocol that manages the FDDI functions provided by the PMD, the
PHY, and the MAC. SMT can run only on a single FDDI ring and can manage
only the FDDI components and functions within a node.
SMT contains three components:
• Connection Management (CMT)
• Ring Management (RMT)
• SMT frame services
CMT
CMT performs these functions:
• Inserts and removes stations at the PHY level
• Connects PHYs and MACs with a node
• Uses trace diagnostics to identify and isolate a faulty component
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