Avaya Configuring Line Services Bedienungsanleitung PDF herunterladen (Seite 34)

Configuring Line Services

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Station Timers

Each node uses three timers to regulate its operation in the ring:

• Token-rotation timer (TRT)

• Token-holding timer (THT)

• Valid transmission timer (TVX)

The TRT times the period between the receipt of tokens. TRT is set to varying

values, depending on the state of the ring. During steady-state operation, the TRT

expires when the actual token rotation time exceeds the TTRT.

The THT controls the length of time that a node can hold the token to transmit

frames. The value of the THT is the difference between the arrival time of the

token and the TTRT.

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.

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Avaya Configuring Line Services Bedienungsanleitung Seite 34