Datacom DM991C, Руководство по эксплуатации продукта

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Product Manual - DM991 Series V Family - 204.4092.08 39
The scheme is very similar to the ones already showed. The external clock coming form the V.35 in the
LTU equipment is passed to the DSL interface, which in its turn is passed to the E1 and digital interfaces
of the NTU equipment. The same happens the other way around (clock coming from the V.35 in the NTU
passes trough the DSL interface and goes to the E1 and digital interfaces in the LTU).
Figure 17. Digital interface External Clocks in Plesiochronous Mode
9.2.3. Synchronous Mode
This mode functions in a similar way as described in the plesiochronous mode, however some details
should be observed:
a. In this mode, the TX and RX should be the same. The user must decide on operating
with internal clock in the LTU and regenerated in the NTU or on making sure that the
external clocks are synchronized.
b. It is not possible to do an external clock loop in the LTU in this mode.
c. When using a regenerated clock, the external equipment should provide the clock with
a minimum accuracy of ±32ppm for proper modem operation.
9.3. Digital Interface Clocks
9.3.1. Clock Source
In this mode the digital interface uses as transmission clock (CT114) the one provided by equipment clock
source.
Figure 18 shows how the V.35 works with Clock Source. The traced arrow indicates that the CT115 is
generated from the DSL interface regenerated clock of the DM991. The CT114 is generated from the
system clock, which in this case, can be internal, regenerated from the line or regenerated from the E1
interface (it can not be regenerated from the digital interface, in which case the use of the CT113 would
be necessary).
Figure 18. Digital Interface Operation with Clock Source
9.3.2. External (CT113)
In this mode the V.35 uses the CT113 (transmission clock of the equipment connected to the DM991) to
generate the o CT114 (transmission clock of the DM991).