HDSL4 System Testing
HDSL4 for General Distribution Installation and Maintenance Practice
16
61223HDSL4L2-5C
The loopback condition imposed in both cases is a logic level loopback at the point within an
H4TU-C module where the DSX-1 signal passes into the HDSL4 modulators.
all of the loopback locations possible with ADTRAN HDSL4 equipment.
In addition to network-side loopbacks, an H4TU-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, Loopback, Control Codes, and Commands”
. In this mode, an AIS
(all ones) signal is supplied to the network.
Figure 8. HDSL4 Loopbacks
X
H4R2 Customer-Side Loopback
DSX-1
AIS
H4TU-C
H4R2
DS1
H4TU-R
H4R1
X = Signal Inactive
H4R2 Network-Side Loopback
DSX-1
H4TU-C
H4R2
DS1
AIS
AIS
H4TU-R
H4R1
X
H4R1 Customer-Side Loopback
DSX-1
AIS
H4TU-C
H4R2
DS1
H4TU-R
H4R1
H4R1 Network-Side Loopback
DSX-1
H4TU-C
H4R2
DS1
H4TU-R
H4R1
X
X
DSX-1
H4TU-C
LOCAL
LOOP
H4TU-C Network-Side Loopback
H4TU-R
H4TU-C
LOCAL
LOOP
H4TU-R Customer-Side Loopback
H4TU-R
H4TU-C
LOCAL
LOOP
H4TU-C Customer-Side Loopback
H4TU-R
X
X
DS1
DSX-1
H4TU-C
LOCAL
LOOP
H4TU-R Network-Side Loopback and/or
H4TU-R NIU Loopback
H4TU-R
X
DS1
DS1
DS1
X
AIS
X
H4R Customer-Side Loopback
DS1
H4TU-C
H4R Network-Side Loopback
H4TU-R
DS1
DSX-1
H4R
DSX-1
AIS
DSX-1
AIS
DSX-1
AIS
AIS
AIS
X
H4TU-C
H4TU-R
H4R