6 Issue 1, December 2003 61223424L2-5A
H4TU-R Network Loopbacks
The loopback position is a logic loopback located
within the H4TU-R internal HDSL4 transceiver. See
Figure 4.
Figure 4. HDSL4 Loopbacks
The H4TU-R responds to multiple loopback activation
processes:
• First, manual loopback on the H4TU-R and/or the
H4TU-C unit may be controlled from the front
panel. Refer to the Front Panel Operation section
of this practice for more detail.
• Second, loopback activation may be accomplished
using the control port of the H4TU-R.
• Third, the H4TU-R will respond to the industry
standard HDSL loopback codes as designated in the
ANSI document T1E1.4/92. These are described in
Appendix A, HDSL4 Loopbacks.
• Fourth, the H4TU-R responds to T1 Network Inter-
face Unit (NIU) loopback codes as described in
Bellcore TR-TSY-000312, as follows:
In-Band Codes
Loop up 11000 (2 in 5)
Loop down 11100 (3 in 5)
ESF Codes
Loop up 1111 1111 0100 1000 (FF 48)
Loop down 1111 1111 0010 0100 (FF 24)
Receiving the in-band codes for more than five seconds
or the ESF codes four consecutive times will cause the
appropriate loopback action. The ESF codes must be
transmitted in the Facility Data Link (FDL).
NOTE
The NIU loopback option must be enabled
before the H4TU-R can respond to the NIU
loopback.
The H4TU-R will respond to the loopback codes by
activating the NIU loopback from either the disarmed or
armed state. The loop down codes will return the
H4TU-R to the disarmed or de-activated state
depending upon the code utilized.
Customer Loopbacks
In addition to the loopbacks in the direction of the
network, the H4TU-R may also be looped back in the
direction of the customer. The H4TU-C and H4TU-R
Customer Side Loopbacks are illustrated in Figure 4.
NOTE
Network and customer loopbacks are governed
by the loopback time out option (Default=120
minutes).
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
DSX-1
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
AIS
X
H4R Customer-Side Loopback
DS1
AIS
AIS
H4TU-C
H4R Network-Side Loopback
H4TU-R
DS1DSX-1
DSX-1
H4R
AIS
AIS
AIS
X
H4TU-C H4TU-RH4R
H4R1 Network-Side Loopback
DS1
SX-1
H4TU-C H4TU-RH4R1 H4R2
AIS
X
H4R1 Customer-Side Loopback
DS1
SX-1
H4TU-C H4TU-RH4R1 H4R2
X = Signal Inactive
X
AIS
H4R2 Network-Side Loopback
DS1
SX-1
H4TU-C H4TU-RH4R1 H4R2
AIS
X
H4R2 Customer-Side Loopback
DS1
SX-1
H4TU-C H4TU-RH4R1 H4R2
X
