Appendix Ahdsl Loopbacks; Figure A-1. Hdsl Loopback Points - ADTRAN T200 Installation And Maintenance Manual

This appendix describes the use and operation of
loopback control code sequences used in ADTRAN's
HDSL system. Loopback control codes are governed
by the HTU-C (and HRE(s) if deployed). Two types
of HTU-Cs exist which enable two different sets of
loopback codes—Standard or Enhanced loopbacks.
The Standard loopbacks are those that have been
contained in ADTRAN's HDSL product family
nd
beginning with 2 Generation products. The
Enhanced loopbacks are contained in selected
ADTRAN HTU-C units. The following table denotes
whether the HTU-C (part number) contains Standard
or Enhanced loopback capabilities.
Standard Loopback
Part Number Description
1242002Lx .............. 220/E220 HTU-C
1242016L1 .............. 3192 HTU-C
1242023L1 .............. DDM+ HTU-C
1244001L1 .............. E220/220 Low Voltage T1 HTU-C
1244002L1-L3 ........ Litespan AHDSL
1244002L4-L6 ........ Litespan AHT1U
th
1245001L1 .............. 5
Voltage HTU-C
th
1245001L2 .............. 5
HTU-C M
1245003L1 .............. 5 th
th
1245004L1 .............. 5
Enhanced Loopback
Part Number Description
th
1245001L4 ............... 5
th
1245003L4 ............... 5
1245004L4 ............... 5 th
th
1245002L6 ............... 5
th
1246001L4 ............... 6
1246003L4 ............... 6 th
1246004L4 ............... 6 th
DSX-1
Interface
61246041L3-5A
HDSL LOOPBACKS
Generation E220/220 Low
Generation E220/220
Generation DDM+HTU-C
Generation 3192 HTU-C
Generation 220/E220 HTU-C
Generation DDM+ HTU-C
Generation 3192 HTU-C
Generation Litespan AHTIU
Generation 220/E220 HTU-C
Generation DDM+ HTU-C
Generation 3192 HTU-C
HDSL REPEATER
HTU-C
HDSL
Loops

Figure A-1. HDSL Loopback Points

61246041L3-5, Issue 1
Appendix A
The HREs and HTU-Rs' loopback capabilities are
controlled from the central office unit (HTU-C).
If the HTU-C on a circuit contains Standard
loopbacks, then refer to subsection 1 of this
appendix to determine its capabilities. If the
HTU-C on a circuit contains Enhanced
loopbacks, then refer to subsection 2 of this
appendix to determine its loopback capabilities.
1. STANDARD LOOPBACKS
This subsection describes operation of the HDSL
system in detection of in-band and ESF facility data
link loopback codes. The operation of the loopback
commands in the ADTRAN HDSL system is
compliant with the recommendation to ANSI recorded
in T1E1.4/92. The HDSL network loopback points
described below are shown in Figure A-1.
HTU-C loopback is a regenerative loopback of the
DSX-1 signal toward the network.
HTU-R loopback is a regenerative loopback of the
DS1 signal toward the network. This loopback is in
addition to a separate Smartjack loopback. Separate
activation sequences are provided for the HTU-R and
the Smartjack loopback initiation. The HDSL
loopbacks are implemented such that the downstream
HDSL elements (toward the customer) remain
synchronized.
Upon deactivation of a loopback, the HDSL system
will synchronize automatically. It should be noted
that the synchronization process of the HDSL system
upon deactivation of the HRE loopback, could take up
to 15 seconds to ensure all system elements are
synchronized.
HTU-R
HDSL
Loops
NOTE
NIU
DS1
Interface
A-1