HDSL2 for General Distribution Installation and Maintenance Practice HDSL2 System Testing
61223HDSL2L2-5B 15
In addition to network-side loopbacks, an H2TU-C module provides customer-side loopbacks
initiated by using either the terminal control port or in-band loop codes. For more infor-
mation, refer to “Appendix A, HDSL2 Loopbacks”. In this mode, an AIS signal (all ones) is
supplied to the network.
Figure 8. HDSL2 Loopbacks
H2TU-R Front Panel Pushbuttons
Two loopback (LBK) pushbuttons are accessible from the front panel of the H2TU-R. The REM
loopback button controls a customer loopback at the H2TU-C. The
LOC loopback button
controls a bidirectional loopback at the H2TU-R. Table 8 details the loopback pushbutton
operation.
Table 8. Front Panel Loopback Pushbuttons
Switch Label Function
REM
Pressing this button changes the H2TU-C loopback state as follows:
• If the H2TU-C is not in loopback, pressing this button will activate a bilateral
loopback.
• If the H2TU-C is in loopback, pressing this button will deactivate the bilateral
loopback.
LOC
Pressing this button changes the H2TU-R loopback state as follows:
• If the H2TU-R is not in loopback, pressing this button will activate a bilateral
loopback.
• If the H2TU-R is in loopback, pressing this button will deactivate the bilateral
loopback.
DSX-1
H2TU-C
LOCAL
LOOP
H2TU-C Network-Side Loopback
H2TU-R
H2TU-C
LOCAL
LOOP
H2TU-R Customer-Side Loopback
H2TU-R
H2TU-C
LOCAL
LOOP
H2TU-C Customer-Side Loopback
H2TU-R
X
X
DS1
DSX-1
DSX-1
DSX-1
LOCAL
LOOP
H2TU-R Network-Side Loopback or
H2TU-R NIU Loopback
DS1
DS1
DS1
X
AIS
AIS
AIS
AIS
X = Signal Inactive
H2TU-C
LOCAL
LOOP
H2TU-R Bilateral Loopback
DS1DSX-1
H2TU-R
H2TU-C
H2TU-R
X
