HDSL4 Maintenance Modes

Appendix A

HDSL4 Loopbacks

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.

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 Table A-1and Table A-2.

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.

61223424L2-5A

A-1

T200 H4TU-R specifications

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