HDSL NEW ENHANCED FEATURE OVERVIEW
HDSL4 for General Distribution Installation and Maintenance Practice
B-10
61223HDSL4L2-5C
Fault (GFI, Short) Bridging
The Fault Bridging feature minimizes circuit downtime by sustaining the circuit during the
impairment until good signal returns, thereby preventing a retrain. Downtime can occur when
an intermittent impairment (GFI, short, micro-interruption, bad splice, noise burst, etc.)
briefly affects the HDSL loop.
Fault bridging addresses two general types of problems:
• brief power fault incidents (lightning)
• brief signal distortions.
In the older generation HDSL4 transceivers, a brief short or GFI would cause a hardware
control to quickly shut down the span power supply for safety reasons. The software would
then detect the power fault and would hold the span supply off for 3 seconds. The HDSL units
would then reinitialize and retrain in approximately 25 to 30 seconds.
In the new enhanced units a combination of hardware and software enhancements allows the
units to sustain communication during brief interruptions in the span supply or brief distor-
tions of the HDSL signal. The hardware will still react to shut down the span supply for the
duration of a power fault to comply with safety requirements; however, the software will wait
much longer (150 msec of fault) before holding the span supply off. This will allow the span
power to return immediately if the power fault disappears. The hardware contains extra
capacitance to help maintain the power supply voltages during this brief interruption of span
power. When the software detects the power fault, the data pump goes into a fault bridging
mode to protect the data pump filters and to maintain service until the anomaly clears.
The software also implements the same fault bridging mode if the HDSL received signal is
distorted out on the loop during a non-power fault event (analog signal micro-interruption) to
keep the data pump stable until the anomaly clears.
NOTE
The Fault Bridging feature is not available with this release of the
1223424L1 Remote unit.
NOTE
The Fault Bridging feature is not available in the H4R Repeaters.
