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097-55501-01 Revision M – January 2009
TimeHub 5500 User’s Guide
33
Chapter 1 Description
Synchronization Status Messaging
Input SSMs
The TimeHub 5500 provides several input-related SSM capabilities. You can
provision the TimeHub 5500 to read the SSM value associated with any input. You
can then use that value to determine which input becomes the active reference
signal. If an input does not have an SSM value associated with it (such as a D4-
framed DS1 input or a 5/10 MHz input), you can assign an SSM value to the input.
The TimeHub 5500 can extract and report the encoded SSM value on any of the
timing inputs using the TL1 keyword CURRSSM. This keyword allows you to
retrieve the SSM value currently associated with a selected input. The value
returned is the Quality Level in
. For detailed syntax, see the description of
this keyword in the TimeHub 5500
TL1 Reference Manual
.
If the input does not support SSMs (for example, D4 framed DS1 and 5/10 MHz
inputs), you can assign an assumed SSM value to the input using the TL1 keyword
QLEVEL. Assigning an SSM allows an input to be automatically selected when the
synchronization mode is set to SSM.
Automatic Reference Switching
You can use the SSM values on the input signal to determine which input is selected
as the active timing reference. The TL1 keyword SYNCMDE provides this control.
SSM is one of the four possible SYNCMODE setting; when SSM is selected, the
CURRSSM value is the primary factor for selecting which input becomes the active
reference (the input must be otherwise qualified for use to be selected). For more
details on setting the sync mode, see
Provisioning Inputs on a Master Shelf
Three factors determine how the TimeHub 5500 selects the active timing reference
from the available qualified input signals:
Stratum 3E Traceable
5
ST3E
Stratum 3 Traceable
6
ST3
SONET Minimum Clock Traceable (20 ppm clock)
7
SMC
Stratum 4 Traceable
8
ST4
DO NOT USE for synchronization
9
DUS
Reserved
10
RES
Table 1-1. SSM Quality Level and Meaning (Continued)
Description
Quality Level
Abbreviation