Comtech EF Data Vipersat SLM-5650A, Installation And Operation Manual

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SLM-5650A Satellite Modem
Revision 10
Appendix B B–16 MN-SLM-5650A
B.3 Clocking Options
Clocking of the data from the terrestrial equipment to the satellite (and vice versa) will depend on
the application. This section describes the most common options and recommended
configurations.
SCT (INTERNAL) clock no longer applies when the modem has loop timing on. The TX clock
source is now recovered from the RX satellite data. This recovered clock is put out on the ST line
and is used to clock the terrestrial equipment. The TX terrestrial clock is now essentially the same
as the RX satellite clock, except that it has been buffered by the terrestrial equipment.
Select TX TERRESTRIAL for the TX clock source when in loop timing, if your equipment is being
slaved off the modem.
B.3.1 IDR/IBS G.703 Master/Master
Use this application when both earth stations have high stability clocks and the received data is to
be clocked to the local network. Refer to Figure B-1 for:
•
Clocking block diagram
•
TX clock options
•
Buffer clock options
The disadvantage of the master/master application is that the RX data will slip, as the clocks will
not be synchronized. If the buffer is properly set up, the slips will be an exact frame length,
causing minimum loss of data. By using very high stability clocks, the expected time between
slips can be several days.
Loss of the buffer clock will mean the buffer will not be emptied and data will not be available. The
buffer clock will normally revert to the low stability internal reference automatically.