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Timing Options
Cascade Timing
The optional T1 Cascade Card extends the network receive T1 data stream to the cascade port. This
makes timing more elaborate than with the basic configuration and results in several timing
variations. The following paragraphs describe variations that are possible with Cascade Timing.
Cascade Timing with a Network Timing Source
As illustrated in
remote end) provides the timing source (1). The SC 553 CSU/DSU recovers the receive T1 clock
from the network receive T1 data and uses it to clock T1 data into the receive buffer
cascade port transmitter (3). The CSU/DSU also translates
channel transmit and receive clock signals on the appropriate interface leads for the channel. The
SC 553 CSU/DSU extends the network receive T1 data stream to the remote equipment connected
to the cascade port, which uses it as a timing reference
(6). The local CSU/DSU recovers the receive T1 clock from the cascade receive DSX-1 (Digital
Service Cross-connect, Level 1) data and uses it to multiplex the DSX-1 data with channel data and
to provide the send timing source for T1 data output from the transmit buffer
Cascade Timing with a Cascade Timing Source
As illustrated in
of the network. All timing and data handling functions internal to the SC 553 CSU/DSU operate as
they would with network timing, and the remote CSU/DSU uses the imbedded timing as its
reference
(2)
and loops it back to the local CSU/DSU (3).
Cascade Timing without the T1 Cascade Card
When the T1 Cascade Card is installed but disabled, or when the card is removed, the SC 553 CSU/
DSU uses the alternate timing source.
D-6
Figure
D-4, when Cascade Timing is selected the network (or a device at the
Figure
D-5, the remote cascade equipment provides the timing source (1), instead
SpectraComm 553 Fractional T1 DSU
Installation and Operation Manual
Timing Option Descriptions
(4)
the receive T1 clock to provide the
(5)
and loops it back to the local CSU/DSU
(7)
(2)
and into the
to the network.
076R155-000
Issue 7
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