Hdsl2 System Testing; Front Panel Operation; Figure 4. Hdsl2 Loopbacks - ADTRAN DDM+ H2TU-C Installation And Maintenance Manual

4. HDSL2 SYSTEM TESTING

The ADTRAN HDSL2 system provides the ability to
monitor the status and performance of the DSX-1
signals, DS1 signals, and HDSL2 loop signals.
Detailed performance monitoring is provided by the
faceplate mounted RS-232 Control Port. These
features are valuable in troubleshooting and isolating
any system level problems that may occur at
installation or during operation of the HDSL2 system.
The following subsections describe additional testing
features.
H2TU-C Loopbacks
The H2TU-C responds to three different loopbacks.
The first of which may be activated using the craft
interface. The Loopback Options Screen which
provides for the H2TU-C and H2TU-R loopbacks is
described in Section 6 of this practice.
Second, the H2TU-C responds to the industry defacto
standard for HDSL2 loopbacks. A detailed
description of these loopback sequences is given in
Appendix A.
Third, the H2TU-C responds to loopbacks initiated
using the operational display located on the faceplate
of the unit. See Section 5 of this practice for details.
This unit contains smartloop technology. That is, if
the unit is optioned to operate in Auto Frame mode, it
constantly monitors the DSX-1 for a framing pattern.
In Auto Frame mode, the unit will initiate the proper
loopback regardless of how the loopback control
sequence is sent (framed or unframed). With the
framing mode set to ESF, SF, or Unframed, the
loopback control code must match the framing format.
The loopback condition imposed in both cases is a
logic level loopback at the point within the H2TU-C
where the DSX-1 signal passes into the HDSL2
modulators. Figure 4 depicts all of the loopback
locations possible with ADTRAN HDSL2 equipment.
In addition to network-side loopbacks, the H2TU-C
provides customer-side loopbacks initiated by using
either the terminal control port or in-band loop codes
(see Appendix A). In this mode, an AIS signal is
supplied to the network.
4
DSX-1
DSX-1
AIS
AIS
DSX-1

Figure 4. HDSL2 Loopbacks

5. FACEPLATE OPERATION
The Faceplate interface consists of a four-character
alphanumeric LED display and two pushbuttons that
control the display. The mode button toggles between
the available options, and the select button allows the
user to choose an option.
The display is used to report the loop margin (dB),
and other operational conditions. In addition, the
display can be used to modify unit configuration and
control loopbacks.
61222003L1-5, Issue 1
H2TU-C Network-Side Loopback
LOCAL
LOOP
H2TU-C H2TU-R
H2TU-R Network-Side Loopback or
(Metallic)
H2TU-R NIU Loopback
LOCAL
LOOP
H2TU-C H2TU-R
H2TU-R Customer-Side Loopback
X
LOCAL
LOOP
H2TU-C H2TU-R
H2TU-C Customer-Side Loopback
X
LOCAL
LOOP
H2TU-C H2TU-R
H2TU-R Bidirectional Loopback
LOCAL
LOOP
H2TU-C H2TU-R
X = Signal Inactive
D = Data Sent
AIS
DS1
X
X
DS1
X
DS1
DS1
DS1
61222003L1-5A