Maintenance Description
9-68 Issue 8.0 July 2002
Synchronization Reference Protection 9
General 9
Synchronization reference protection switching occurs in response to
automatically detected faults and external commands from a local/remote CIT or
operations system. Refer to the FAULT-Switch-Synchronization input in
Volume I, Section 11, "Craft Interface Terminal Usage."
Table 9-11 shows the standard protection switching priorities in descending order
of priority used by the FT-2000 OC-48 Add/Drop-Rings Terminal.
DS1 Reference Protection 9
In the externally timed mode (phase locked mode in releases prior to Release 5),
the TG3 (DS1) circuit packs on the Low Speed Shelf - System Controller derive
timing from two external DS1 reference signals as shown in Figure 9-23.
The number 1 TG3 (DS1) circuit pack accepts the primary DS1 reference signal
and the number 2 TG3 (DS1) circuit pack accepts the secondary DS1 reference
signal.
If the primary DS1 reference signal fails, the FT-2000 OC-48 Add/Drop-Rings
Terminal switch to the secondary DS1 reference signal and the number 2 TG3
(DS1) circuit pack. If both DS1 reference signals fail, the TG3 (DS1) circuit pack
holds the on-board oscillator frequency at the last good reference sample
(holdover mode) until the DS1 reference signals are repaired. In the holdover
mode, the on-board oscillator frequency will not degrade below the stratum 3
level.
Table 9-11. Synchronization Reference Protection Switching Priorities
Switch Priority (Descending Order) Source of Request
Reset* CIT/OS
Lockout CIT/OS
Forced switch CIT/OS
Signal failure Automatic
Manual switch CIT/OS
Wait to restore Automatic
* Resetting the synchronization switch priority
(FAULT-Switch-Synchronization- Reference-Priority:Reset) has
no effect on any automatic switch priority except wait to restore.
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