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42 097-55501-01 Issue 6 – June 2003

TimeHub 5500 System Guide

1.5.3 Details of Remote SSM Behavior

Table identifies how the source of SSM will be determined in a remote

shelf for a variety of conditions. Other than the special case where the

OMANSSM keyword is used to manually set the output SSM value (see

TL1 Reference manual for details), the SSM source determines the SSM

that will be encoded on any ESF-framed DS1 outputs generated on the

remote shelf.

5 If the previous step of this procedure succeeded, the remote shelf is now able to use this

DS1 input 1 signal as an SSM source. The "A" (Active) LED indicates that this input is

currently being used as the source of SSM information for the remote shelf. When lit, any

outputs carrying SSM will be encoded with the same SSM value that is being decoded on

this input. The "A" LED will illuminate as long as none of the following conditions are

present:

• There isn't also a qualified SSM input in the DS1 input 2 row. If there is, it is possible

that this input will be selected as the active SSM source instead of the DS1 input 1

signal. When both SSM inputs are valid the one that will be used is determined by

the setting of the PRIORITY keyword. The default is that the DS1-1 input has the

higher priority, so it will be selected when both inputs are qualified. See TL1 manual

for details.

• There isn't an active CC timing reference. If the remote shelf isn't actively following

one of its CC timing inputs (which means the shelf is in holdover operation) it doesn't

make sense to use either of the DS1 SSM inputs. The intent of these SSM inputs is

to convey the SSM of the CC timing references so, if the CCs aren't being used, the

SSM inputs shouldn't be either. If this condition is present (easily verified by no "A"

LED on either CC input row), follow the procedure "Procedure for Configuring and

Using Either CC1 or CC2 as Timing Reference" to activate a timing reference. Once

accomplished the "A" LED on the DS1 input 1 row should also light.

End of Procedure

Table 1-2. SSM Source Determination for Remote Shelf

Condition SSM Source

Shelf has no active timing reference ("A" is

not lit in either CC1 or CC2 row).

The SSM value is that of the internal oscillator in

the active clock card (see HFQLEVL keyword in

TimeHub TL1 Reference Manual).

Procedure 1-2. Using DS1 Inputs for SSM Decoding on a Remote Shelf (Cont’d)

Step Action

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