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Maintenance Object Repair Procedures
555-233-123 10-1786 Issue 4 May 2002
Manual EPN Tone-Clock Interchange
In an EPN with duplicated Tone-Clock circuit packs, one circuit pack is always
preferred over the other. This is the Tone-Clock circuit pack in carrier A. The
intention is that the preferred circuit pack be active whenever it is healthy. Once a
failing preferred Tone-Clock circuit pack has been replaced or repaired, the
system will make it active as soon as possible.
Control over interchanges for an EPN is accomplished in essentially the same
ways as items 1 and 3 in the PPN case above. In addition, when the
non-preferred Tone-Clock circuit pack in an EPN is active, and the preferred
circuit pack is repaired and proven capable of filling its roles, the system will
automatically interchange back to it as soon as possible.
Software Maintenance Interchange
Interchanges may be instigated by software Tone-Clock maintenance in two ways.
1. A scheduled Tone-Clock circuit pack interchange occurs according to the
parameters set by the change system-parameters maintenance
command. This can be disabled or set to run weekly, but the standard
(default) situation is for it to occur daily, at the time specified in the
system-parameters list for scheduled maintenance to begin. This
interchange will be blocked if the lock switches are set, if the non-preferred
Tone-Clock circuit pack in an EPN has been selected with the set
tone-clock command, if the standby Tone-Clock has been set to the
busyout state, or if the clock generation capability of the standby
Tone-Clock circuit pack is known to be impaired. When this scheduled
interchange occurs, the standby Tone-Clock circuit pack becomes active
for a period of 20 seconds to test its ability to generate clock signals, and
then is returned to standby mode.
2. Unscheduled interchanges occur when on-board Tone-Clock circuit pack
maintenance, or ongoing switch maintenance tests of TONE-BD,
TONE-PT, or TDM-CLK uncover failures serious enough to raise any
MAJOR or MINOR alarm against the active Tone-Clock circuit pack.