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5−
17
clock card will reproduce it and send it out via the output card. As an example,
the received SSM is Primary Reference Source (PRS) and its bit pattern is
0000010011111111 (refer to Table 5-A). The 54500 system will transmit this
message so that, at the output, the system will be able to detect that the SSM
equals PRS.
If the input DS1 is lost, the active clock card will go to holdover mode and then
output the SSM that is equal to its own stratum level. Removal of the input
DS1 causes the StarClock 200E system to act in the following sequence:
1. Display number 9 indicates LOS.
2. 54550 sends the LOS message to the terminal interface.
3. Clock card goes to HOLDOVER.
4. Output is STRATUM 3 SSM.
5. 54550 sends the current SSM status to the terminal interface. (For the
54522, it is Stratum 3.)
If the active clock card receives an SSM that is lower than its own stratum
level, it will treat the case as LOS.
If there is no SSM in the DS1 input, the clock will send out STU
(Synchronization Traceability Unknown), e.g. ESF with no code word or SF.
If one input DS1 has a higher level of sync status, the clock card will
automatically switch to input the higher level DS1.
During input tracking, if the input SSM changes, the clock card will change its
output SSM accordingly within 5 seconds.
Table 5-A
Prioritized Synchronization Status Messages
Description
Priority Level
DS1 ESF Data Link
Code Word
Abbreviation
Stratum 1 Traceable
1
0000010011111111
PRS
Synchronized -
Traceability Unknown
2
0000100011111111
STU
Stratum 2 Traceable
3
0000110011111111
ST2
Stratum 3 Traceable
4
0001000011111111
ST3
±20 ppm Clock
Traceable
5
0010001011111111
SIC
Stratum 4 Traceable
6
0010100011111111
ST4
DON'T USE for
Synchronization
7
0011000011111111
DUS
X
Reserved
RES
