Appendix Ahdsl2 Loopbacks - ADTRAN T200 Installation And Maintenance Practice

HDSL2 MAINTENANCE MODES
This appendix describes operation of the HDSL2
system with regard to detection of inband and ESF
facility data link loopback codes.
Upon deactivation of a loopback, the HDSL2 system
will synchronize automatically.
Loopback Process Description
In general, the loopback process for the HDSL2 system
elements is modeled on the corresponding DS1 system
process. Specifically, the H2TU-C loopback is similar
to an Intelligent Office Repeater loopback, and the
H2TU-R loopbacks are similar to an in-line T1 Repeater
loopback.
Inband control code sequences are transmitted over the
DS1 link by either the unframed or overwrite method.
The HDSL2 elements respond to either method.
The unframed method produces periodic control
sequences, and the normal DS1 framing bit is omitted.
The overwrite method produces periodic control
sequences. However, once per frame, the framing bit
overwrites one of the bits in the control sequence.
The unit can detect the loopback activation or deacti-
vation code sequence only if an error rate of 1E
better is present.
61223024L2-5A
Appendix A
HDSL2 Loopbacks
or
-03
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DDS Latching Loopback Operation
If the unit is optioned for FT1 mode, then DDS Latching
Loopback operation is supported as described in
Bellcore TA-TSY-000077, Issue 3, Section 5.1.3. The
H2TU-C in the HDSL2 circuit is treated as an Identical
Tandem Dataport, and the H2TU-R is treated as a
Different Tandem Dataport. The H2TU-R will establish
a network loopback upon detection of standard DDS
NI-NEI/RPTR loopback sequence.
Loopback Control Codes
A summary of control sequences is given in
and Table A-2.
NOTE
In all control code sequences presented, the
inband codes are shown left-most bit trans-
mitted first, and the ESF data link codes with
right-most bit transmitted first.
Table A-1
A-1