Symmetricom SSU-2000e User Manual page 25

The Input modules make phase measurements between the input signal and the
clock oscillator(s). From these phase measurements, the Input modules compute
frequency offset and wander of the input signals. Wander is reported in terms of
Maximum Time Interval Error (MTIE) and Time Deviation (TDEV). The data is then
stored for use in the SSU-2000e and reported through the Communications module.
You can install one or two GPS input modules that use the satellite-based Global
Positioning System signals as a synchronization reference. The input signal types
supported are:
DS1/Clock (unframed)
E1/Clock (unframed)
GPS
Composite Clock
Selecting the Input
Many factors influence which input reference the SSU-2000e uses:
Priority
PQL/SSM
Switching mode
User-assigned Input State
Active alarms on an input
You can provision the SSU-2000e to automatically select the highest-quality input
signal, or you can manually select the input signal you want to use. Two factors
determine the quality of the input: the user-defined Priority level, and the PQL/ SSM.
These factors are used to determine which input is used, and what happens if that
input becomes disqualified.
Priority Level
You can assign a Priority level to each input; this value helps determine which input
is used as the system reference. The range is 0 to 10; the lower the Priority level,
the higher the priority. Use the TL1 command SET-PRMTR-INPUT or the ICS
command INPUT to provision these parameters. See
Mode, on page 26, for details on using the Priority level.
SSMs and Quality Level
Synchronization Status Messages (SSMs) may be included in the bit stream of the
incoming signal to indicate its quality level. To read the incoming SSM, you must
provision the input to read the SSM; for E1 signals, you must provision the bit
position of the incoming SSM. Use the TL1 command SET-PRMTR-INPUT or the
ICS command INPUT to provision these parameters.
12713140-002-2 Revision E – October 2006
Chapter 1 Product Overview
System Architecture
Setting the Input Selection
SSU-2000e User's Guide 25