Avaya S8700 Maintenance Manual page 970

Maintenance-Object Repair Procedures
PNC Interchanges
PNC spontaneous interchanges occur when PNC duplication software determines
that the standby PNC's state of health (SOH) surpasses the active PNC's.
PNC-DUP executes a spontaneous interchange in response to a message
from a PNC component MO indicating that either a fault has occurred on
the active PNC or a fault has been resolved on the standby PNC.
The PNC SOH is compared to the standby PNC, and an interchange
occurs if the standby PNC's state of health surpasses the active PNC's.
A corresponding Major or Minor alarm is logged by the reporting MO,
stimulating an alarm report.
When the resolution of a fault on the standby renders it more healthy than a
simultaneously-faulted active PNC, the error message indicates the type and
location of the improved component.
Once the interchange completes, the failed component is on the standby PNC. A
demand interchange can be requested in the presence or absence of standby
PNC faults. The following sequence of actions can be observed during a
fault-free interchange:
1. The ATM-Expansion Interfaces currently acting as archangels in the EPNs
are deactivated as indicated by the amber LEDs going from flashing to on
solid.
2. The ATM-EIs in IPSI port networks are interchanged, indicated by the new
standby ATM-EI amber LED off and the new active ATM-EI amber LED on
steady.
3. One by one the EPN ATM-EIs in non-IPSI port networks are interchanged
as indicated by new standby ATM-EI amber LED turning off and the new
active ATM-EI amber LED flashing (2 seconds on / 200 milliseconds off).
At this point, the interchange is functionally complete.
Certain conditions may interfere with the normal execution of the interchange:
1. In a faulted spontaneous interchange, it is possible the EPN/EPNs directly
affected by the fault will be the last to interchange.
2. A user directly affected by the single fault instigating a PNC interchange
can experience a momentary voice path outage during the switch.
3. If faults exist on both the standby and active PNC, it is possible to have
some EPNs go out of service while others are returned to service.
In any multifault situation, rely on status pnc to determine which is the active
PNC.
PNC duplication informs Timing Synchronization maintenance when a PNC
interchange has been completed and indicates which PNC is active. This causes
Synchronization to audit and ensure that the primary source for synchronization of
Tone-Clocks in each EPN is supplied by a path associated with the active PNC.
8-248 Issue 1 May 2002 555-233-143