Symmetricom SDU-2000, User Manual

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12713020-002-2 Revision D – April 2004 SSU-2000 User’s Guide 33
Product Overview
System Architecture
Output Section
The output section contains from one to six (three redundant pairs) Output modules
in the main shelf and up to 56 (28 redundant pairs) Output modules in a fully
expanded system with four SDU-2000 expansion shelves. Each Output module
type provides 20 independent output synchronization signals. Output modules are
available to support the following formats:
DS1, SF (D4) and ESF
E1
2048 kHz
Composite Clock (CC) (64/8 kHz)
Other typical clock frequencies
Clock Section
The clock section consists of one or two Clock modules that provide the internal
reference signals for generating TSG output timing signals. The primary Clock
module (Clock A) is configured as the master clock and is normally a higher stratum
level than the back-up clock (Clock B). If a problem occurs in Clock A, the control is
automatically passed to the back-up Clock module (Clock B). The frequency of each
clock is locked to a valid reference input signal (one that is free from input faults
while meeting acceptable frequency and MTIE specifications).
The SSU-2000 controls clock frequency by adjusting the control value of the Direct
Digital Synthesis (DDS) function in each Clock module. The adjustments are
processor-controlled and based on measurements performed and computed in the
Input module(s). Clock modules may be Stratum 2E and Stratum 3E. Outputs are
maintained by the active input reference signal if both clocks should ever fail or be
removed from the system.
Communications Section
The Communications section consists of one Communications module, which
contains hardware and software that allows the user to configure, monitor, and
control the SSU-2000 system and generate local and remote alarms when fault
conditions are detected. The SSU-2000 can continue to function seamlessly without
the Communications module (Clock modules assume the system controller
function), but all communications and alarm reporting functions are interrupted.
The master controller function for the SSU-2000 can reside in either the
Communications module or in either of the clock modules. The priority of the
selection of the module that will provide the master controller function rests with the
Communications module, Clock A, and Clock B, in that order. In the event of
removal of the module designated as the master controller, that function
automatically and seamlessly switches to the next module in priority order.