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Timing Options
Typical Network Applications
Although you can use the SC 553 CSU/DSU in various network configurations with different types
of equipment, the following simple applications illustrate the fundamental reasoning you use to
select the appropriate timing option.
Back-to-Back Application
In an in-house data communications network, two SC 553 CSU/DSUs are connected back-to-back.
The only component connecting them is cable, so there is no network to provide the timing source.
If the customer equipment connected to the channels cannot provide timing, select Internal Timing
for the master or host end, and select Slave Timing for the other, as shown in
example, the SC 553 CSU/DSU at Site A is configured for Internal Timing, making it the timing
source.
If the customer equipment is to provide an external timing source, select Channel Timing (External/
DTE Timing) for the CSU/DSU connected to that equipment and select Slave Timing for the other,
as shown in
Figure
its CSU/DSU is configured for Channel Timing (External/DTE Timing).
In the master/slave multiplexer application illustrated in
configured as the master (i.e., the timing source) and the multiplexer at Site B is configured as a
slave. By selecting Channel Timing (External/DTE Timing) for both CSU/DSUs, the master
multiplexer provides timing and the slave multiplexer loops back timing, so timing is dependent on
the customer equipment.
D-10
D-7B. In this example, the host computer on the channel is providing timing, so
SpectraComm 553 Fractional T1 DSU
Installation and Operation Manual
Typical Network Applications
Figure
Figure
D-7C, the multiplexer at Site A is
076R155-000
Issue 7
D-7A. In this
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