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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
1242002Lx ............. 220/E220 HTU-C
1242016L1 ............. 3192 HTU-C
1242023L1 ............. DDM+ HTU-C
1244001L1 ............. E220/220 Low Voltage
1244002L1 - L3 ..... Litespan AHDSL
1244002L4 - L6 ..... Litespan AHT1U
1245001L1-L2 ....... E220/220 Low Voltage
1245003L1-L2 ....... DDM+ 5
1245004L1-L2 ....... 3192 5
Enhanced Loopback
Part Number
1245001L4-L8 ....... E220/220 HTU-C
1245002L6 ............. Litespan AHT1U
1245003L4-L8 ....... DDM+ HTU-C
1245004L4-L8 ....... 3192 HTU-C
1246001L4-L8........E220/220 HTU-C
HTU-C
DSX-1
Interface
61246045L1-5B
Appendix A
HDSL Loopbacks
Description
T1 HTU-C
5
th
Gen HTU-C
th
Gen HTU-C
th
Gen HTU-C
Description
HRE #1
HDSL
Loops
Figure A-1. HDSL Loopback Points
Section 61246045L1-5, Issue 2
1246003L4-L8........DDM+HTU-C
1246004L4-L8........3192 HTU-C
The HREs and HTU-Rs' loopback capabilities are
controlled from the central office unit (HTU-C).
NOTE:
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.
A-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
Figures A-1 and A-2.
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.
HRE #2
HTU-R
HDSL
Loops
NIU
DS1
Interface
A-1
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