Avaya S8700 Maintenance Manual page 480

Maintenance Object Repair Procedure
For IPSI Port Networks, unscheduled IPSI/Tone-Clock interchanges may
occur any time as a part of an unscheduled IPSI interchange. The IPSI
interchange may be the result of Tone-Clock, PKTINT, or EAL faults.
2. In an EPN with duplicated Tone-Clock or IPSI circuit packs, one circuit pack
is always preferred over the other. For the first port network in a cabinet,
this is the Tone-Clock or IPSI circuit pack in carrier A. If a second port
network is configured in a cabinet, its preferred Tone-Clock or IPSI circuit
pack is located in carrier E. The intention is that if the preferred Tone-Clock
or IPSI circuit pack has been replaced or repaired, the system will make it
active by interchanging to it as soon as possible.
Firmware Instigated Tone-Clock Interchanges
Firmware-initiated Tone-Clock interchanges occur when the auto clock switching
option is enabled, and the TN2312 IPSI circuit pack firmware detects a loss of
clock or clock errors. After detecting a loss of clock/clock errors, and rather than
waiting for S8700 IP Connect software to request a switch, the IPSI firmware will
automatically switch the clock (when auto clock switching is enabled). The auto
clock switching option is disabled during system restarts.
NOTE:
The auto clock switching option is required by the IPSI circuit pack since the
EAL connection to the PKTINT (one of the IPSI circuit packs many
functions) is over the S8700 IP Connect packet bus which must have a good
clock for proper operation.
Clock Synchronization
This section discusses synchronization with a Stratum-4 clocking device.
Stratum 4
In G3r, a PPN always resided in the system and was used as a backup
synchronization source when either a:
Synchronization source was not administered
Designated master and secondary synchronization source failed
With Stingray, EPN 1 (PPN) may or may not exist and thus cannot be relied on as
the backup synchronization source. If a Stingray system does not have an
administered synchronization source, it uses the first EPN that comes up as its
source. If the designated master and secondary synchronization sources fail, the
system uses any other EPN as its source. No preference is given to EPN 1.
8-1176 Issue 1 May 2002 555-233-142