Appendix Ahdsl4 Loopbacks; Loopback Process Description - ADTRAN T200 H4TU-R Installation And Maintenance Practice

HDSL4 MAINTENANCE MODES
This appendix describes operation of the HDSL4
system with regard to detection of inband 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 in-line 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.
61223424L2-5A
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 deacti-
vation code sequence only if an error rate of 1E-03 or
greater is present.
Loopback Control Codes
A summary of control sequences is given in
and Table
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.
A-2.
NOTE
Table A-1
A-1