Instruction manual

System Timing
Considerations
This section explains the timing modes and clock rates available for the main link
of the DV-MUX3, and for its data and voice channels.
Main Link Timing The main link transmit and receive paths of the DV-MUX3 require external re-
ceive and transmit clock signals derived from the network clock. The transmit and
receive clock must be derived from the same source. DV-MUX3 will however tol-
erate phase difference and jitter between the two clocks. Therefore, when the two
DV-MUX3 units are connected through a modem link, one of the modems must be
configured for operation with its internal clock, and the other must use loopback
timing (operation on the recovered receive clock).
The main link clock signals always determine the DV-MUX3 receive and transmit
timing. Thus, the DV-MUX3 always distributes downward the system timing.
The main link rate (any standard rate in the range of 9.6 to 256 kbps) is automat-
ically identified by actually measuring the clock frequency. The DV-MUX3 will
provide an alarm indication if the measured frequency is not close enough to one
of the supported main link rates.
Data Channel Timing The data channel supplies receive and transmit clock signals derived from the link
clock to the attached equipment, and expects the user equipment to accept and gen-
erate data in accordance with these signals.
NOTE
When using the DV-MUX3 adaptive mode, it is strongly rec-
ommended to operate the equipment connected to the data
channel with independent transmit and receive clock signals.
This prevents the possibility of short error bursts occurring
when dynamic bandwidth reallocation is performed.
When it is not possible to use independent transmit and receive
clock signals, e.g., when the X.21 interface is used, and the oc-
currence of error bursts is undesirable, it is recommended to
use the non-adaptive mode.
Voice Channel Timing The voice channel digitizing rate (4.8, 6.4, 7.2, 9.6 or 12.8 kbps) is always locked
to the main link receive clock.
TYPICAL APPLICATIONS AND SYSTEM DESIGN CONSIDERATIONS
DV-MUX3 Installation and Operation Manual 1-13