ADTRAN HDSL2 Installation And Maintenance Practice

Also see for 1223024L2: Installation and maintenance practice Manual

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ADTRAN HDSL2 Installation And Maintenance Practice Manual pdf 82 page image

HDSL New Enhanced Feature Overview HDSL2 for General Distribution Installation and Maintenance PracticeB-10 61223HDSL2L2-5Bpower. When the software detects the power fault, the data pump goes into a fault bridgingmode 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 isdistorted out on the loop during a non-power fault event (analog signal micro-interruption) tokeep the data pump stable until the anomaly clears.Fast Retrain FeatureFast Retrain is an ADTRAN proprietary feature whose intent is to minimize downtime when anintermittent non power-related impairment (bad splice, noise burst, etc.) affects the HDSLloop and cannot be bridged.HDSL-2 and HDSL-4 transceivers normally train in approximately 25 to 30 seconds. For aninitial circuit turn-up, this is not a big issue. However, once service has been established onthe circuit, any large down-time will interrupt communications on the circuit. A loss ofsynchronization on the HDSL loop can cause excessive down times due not only to the 30second HDSL retrain time, but also further delays due to the higher level protocols in thenetwork 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. Thisretrain 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 triggerhigher level protocol re-synchronizations.In an effort to minimize this down time, the Fast Retrain feature has been implemented. If animpairment (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. Thisabbreviated train can achieve data mode in 5 to 7 seconds. A successful fast retrain should beevident by watching the Span Status screen and by reduced unavailable seconds (UAS) in thePM data for each LOS alarm recorded.NOTEFast-Retrain capable units must be installed on both ends of theHDSL2 circuit for this feature to function properly. Also, if there isa failure of a fast retrain attempt, for any reason, then the tradi-tional (25-30 second) retrain will be initiated.