tem can recover when the FDDI class A configuration issued. The first involves the loss of a node processor attached to a network interface unit. When this occurs, an optical bypass can be configured to its bypass state, which enables data to flow through the station to the disabled station. This keeps the ring operating although the malfunctioning station's processor is lost.
The second type of failure occurs when there is a "fatal" link error in the primary ring of the dual ring configuration. This causes the loss of communication on that ring. When this occurs, all data transfers are moved to the secondary ring and the use of the failed primary ring is halted. Since this effectively removes all class B stations from the previous ring environment, such stations should be used in noncritical network connections, only.
The third type of failure occurs when a node interface unit (NIU) is lost, the dual rings between the two NIUs both fail, or a NIU is isolated because of link failures. Recovery for this type of failure uses a loop back feature, which routes all incoming data back along the other fiber in the same cable. Each station except those
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