Appendix Ahdsl4 Loopbacks - ADTRAN H4TUC 3192 Installation And Maintenance Practice

HDSL4 MAINTENANCE MODES
This appendix describes operation of the HDSL4
system with regard to detection of in-band and ESF
facility data link loopback codes. Upon deactivation
of a loopback, the HDSL4 system will synchronize
automatically.
Loopback Process Description
In general, the loopback process for the HDSL4
system elements is modeled on the corresponding
DS1 system process. Specifically, the H4TU-C
loopback is similar to an Intelligent Office Repeater
loopback, and the H4TU-R loopbacks are similar to
an inline T1 Repeater loopback.
In-band control code sequences are transmitted over
the DS1 link by either the insert or overwrite method.
The HDSL4 elements respond to either method. The
insert method produces periodic control sequences
that are not overwritten by the DS1 framing bits.
61222404L1-5B
Appendix A
HDSL4 Loopbacks
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
deactivation code sequence only if an error rate of 1E-
03 or better is present.
Loopback Control Codes
Control sequences are summarized in Table A-1 and
Table A-2.
In all control code sequences presented, the in-
band codes are shown with the left-most bit
transmitted first, and the ESF data link codes
with right-most bit transmitted first.
NOTE
A-1