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STRAT-3 (Stratum 3 Clock)
Issue 4 May 2002 10-1557 555-233-123
10
STRAT-3 (Stratum 3 Clock)
The Digital Synchronization Network Plan (PUB 60110) specifies a hierarchy of
synchronization nodes consisting of strata 1 to 4, where the sole Stratum 1 clock
in the network is the most accurate. DEFINITY supports both Stratum 3 and
Stratum 4 operations. Refer to SYNC (Synchronization) Maintenance
documentation for details on Stratum 4 operation.
A Stratum 3 clock derives its timing from two DS1 references that are connected
to a Stratum 3 or better (that is, lower stratum) source. The Stratum 3 clock
provides a holdover of at least 24 hours should both DS1 references fail. (After 24
hours, the Stratum 3 clock still provides service but its accuracy may be
degraded). The Digital Synchronization Network Plan (PUB 60110) requires that
the Stratum 3 clock have duplicated components.
The recognition of the Stratum 3 clock itself as well as its alarm signals, is
supported only by the TN780 Tone-Clock circuit pack. The TN780 Tone-Clock
circuit pack is also backwards-compatible with the TN768 Tone-Clock circuit pack.
The Stratum 3 clock may be connected to either the PPN or an EPN if the TN780
Tone-Clock circuit pack(s) is present in that port network. However, for reliability, it
is recommended that the clock be connected to the PPN.
The only operation that software can perform is a query of the alarm leads. The
only recovery action that can be performed on a catastrophic failure of the
Stratum 3 clock is the utilization of the local oscillator on the Active TN780
Tone-Clock circuit pack. Neither software nor the TN780 Tone-Clock circuit pack
can request additional information about the health of the Stratum 3 clock other
than the information provided by the alarm leads. Furthermore, neither the
software nor the TN780 Tone-Clock circuit pack can request that the external
clock switch references, change configuration, disable/enable, initialize, etc.
In G3iV1.1-286 and G3iV2-386, the Stratum 3 clock has been implemented as an
external that follows the specification in PUB 60110 for Stratum 3.
Figure 10-90 on
page 10-1558 shows how the Stratum 3 hardware configuration provides clock
and alarm signals to the TN780 Tone-Clock circuit pack(s). The reference DS1
facilities are connected directly to the Stratum 3 clock for timing purposes, but the
DS1 data may be routed into the switch by using a Y connector.
MO Name (in
Alarm Log)
Alarm
Level Initial Command to Run Full Name of MO
STRAT-3 MAJOR test synchronization Stratum 3 Clock
STRAT-3 MINOR test synchronization Stratum 3 Clock
STRAT-3 WARNING test synchronization Stratum 3 Clock