HDSL New Enhanced Feature Overview HDSL2 for General Distribution Installation and Maintenance Practice
B-10 61223HDSL2L2-5B
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.
Fast Retrain Feature
Fast Retrain is an ADTRAN proprietary feature whose intent is to minimize downtime when an
intermittent non power-related impairment (bad splice, noise burst, etc.) affects the HDSL
loop and cannot be bridged.
HDSL-2 and HDSL-4 transceivers normally train in approximately 25 to 30 seconds. For an
initial circuit turn-up, this is not a big issue. However, once service has been established on
the circuit, any large down-time will interrupt communications on the circuit. A loss of
synchronization on the HDSL loop can cause excessive down times due not only to the 30
second HDSL retrain time, but also further delays due to the higher level protocols in the
network going through re-synchronization. On the older generation HDSL2 and HDSL4 units,
a 1-second loss of HDSL frame synchronization would cause the data pumps to retrain. This
retrain would take approximately 25 seconds during which AIS would be sent to the termi-
nating equipment. The reception of AIS by the terminating equipment then might trigger
higher level protocol re-synchronizations.
In an effort to minimize this down time, the Fast Retrain feature has been implemented. If an
impairment (bad splice, for example) causes the HDSL data pump to lose frame synchroni-
zation for 500 msec or longer, instead of retraining, a fast retrain will be attempted. This
abbreviated train can achieve data mode in 5 to 7 seconds. A successful fast retrain should be
evident by watching the Span Status screen and by reduced unavailable seconds (UAS) in the
PM data for each LOS alarm recorded.
NOTE
Fast-Retrain capable units must be installed on both ends of the
HDSL2 circuit for this feature to function properly. Also, if there is
a failure of a fast retrain attempt, for any reason, then the tradi-
tional (25-30 second) retrain will be initiated.
