include LL and DL loopbacks, controlled by top panel keypads and
LCD-menu. Maintenance is further enhanced by a power-up self-test.
Selection of System Timing Mode
This section explains the interaction between the user’s port timing
mode, and the E1 link transmit timing mode.
z
Internal timing mode:
The WireSpan 600 / 610 E1 link
transmit signal is derived from the internal clock oscillator.
This timing mode used is necessary in point-to-point
application over leased lines, e.g., short-range applications,
where one WireSpan 600 / 610 must provide the timing
reference for the link. In this case, one WireSpan 600 / 610
must use the internal oscillator, and other must operate on the
recovered clock signal. Note that when the internal oscillator
is used, the DCE or DTE timing mode should be selected to
synchronize the user data rate to the E1 link timing.
Figure 1-5
shows a typical system application using the internal
timing mode on conjunction with DCE timing.
DTE / DCE
N x 64K
Converter
WireSpan 600
WireSpan 600
DTE / DCE
Internal Timing
E1 Timing
E1
RS-449
X.21
Figure 1-5 Internal timing mode
z
E1 timing mode:
With E1 timing, the WireSpan 600 /
610 link transmit signal is locked to the recovered E1
receive clock. This is usually the timing mode selected
for network operation, as shown in
Figure 1-6.
In the
application illustrated in
Figure 1-6
, the master clock of
the network determines the timing of the two WireSpan
600 / 610 units. In case the E1 receive signal is lost,
WireSpan 600 / 610 automatically switches to the
internal oscillator.
1-6
