Juniper CTP2000 Series Hardware Documentation page 44

CTP2000 Hardware Documentation
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If a T1/E1 module is installed in the slot that is closest to the processor, a spoke RTM
is not needed behind any T1/E1 modules. They will synchronize to the H.100 clock.
For platforms with only nonvoice boards (serial or T1/E1 module), only a main RTM is
needed for external clock reference input.
NOTE: The clock RTM is installed in the rear of slot 0 next to the CPU slot.
When you upgrade from an older processor to a PP833 processor, you can
leave the CPU RTM in the chassis. Leaving the CPU RTM in the chassis will
not adversely affect the functioning of the PP833 processor. Leaving the
RTM installed will provide proper airflow within the CTP node.
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