Appendix Ahdsl2 Loopbacks - ADTRAN DDM+ H2TU-C Installation And Maintenance Manual

HDSL2 MAINTENANCE MODES
This Appendix describes operation of the HDSL2
system with regard to detection of in-band 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 inline T1 Repeater loopback.
In-band 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.
61222003L1-5A
Appendix A
HDSL2 Loopbacks
The unit can detect the loopback activation or
deactivation code sequence only if an error rate of
-03
1E or better is present.
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 and any H2R units
which are in the HDSL2 circuit are treated as
Identical Tandem Dataports 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 Table
A-1 and Table A-2.
In all control code sequences presented, the
in-band codes are shown left-most bit
transmitted first, and the ESF data link codes
with right-most bit transmitted first.
Section 61222003L1-5, Issue 1
NOTE
A-1