Hdsl Loopbacks; Hdsl Maintenance Modes; Loopback Process Description; Loopback Control Codes - ADTRAN HDSL DDM+ HTU-C Installation And Maintenance Practice

HDSL MAINTENANCE MODES

This Appendix describes operation of the HDSL system with regard to detection of in-band and
ESF facility data link loopback codes.
Upon deactivation of a loopback, the HDSL system will synchronize automatically. Note that
the synchronization process of the HDSL system upon deactivation of the HRE loopback could
take up to 15 seconds, ensuring all system elements are synchronized.

Loopback Process Description

In general, the loopback process for the HDSL system elements is modeled on the corre-
sponding DS1 system process. Specifically, the HTU-C loopback is similar to an Intelligent
Office Repeater loopback and the HTU-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 HDSL 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 deactivation code sequence only if an error rate
of 1 -03 or better is present.

Loopback Control Codes

A summary of control sequences is given in.
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.
61247003L6-5A
Appendix A

HDSL Loopbacks

NOTE
A-1