61223HDSL4L2-5C
A-1
Appendix A
Loopback, Control Codes, and Commands
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 corre-
sponding 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.
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 greater is present.
Loopback Control Codes
A summary of control sequences is given in
and
.
NOTE
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.
