PairGain 150-1141-05, Manual, Page: 52 / 78

Troubleshooting 150-388-105-05, Revision 05
44 March 25, 2000 HLU-388 List 5
L
OOPBACK
O
PERATION
HiGain has a family of loopback options for analyzing circuit functionality. The loopback signal is transmitted
and returned to the sending device for comparison. This verifies the integrity of the HDSL channels to the HLU,
of the HLU DSX-1 interface, and of the DS1 channels to the customer.
Loopback options include:
• Generic Loopback (GNLB) options, including the SmartJack (SMJK) option ( Table 14 on page 45 )
• Special Loopback (SPLB) options, including “Special Loopback Commands” on page 46 and the following
tables:
– Addressable Repeater Loopback commands: A1LB, A2LB, A5LB ( Table 15 on page 50 )
– Addressable Repeater Loopback commands: A3LB, A4LB ( Table 16 on page 53 )
Loopback commands can be initiated by:
• selecting the loopback type using the MODE and SEL buttons on the HLU (or the Manual Loopback button
on the HRU)
• selecting the loopback type from the Maintenance Terminal Main Menu when connected to the craft port of
the HLU or HRU
• entering the loopback code into the test equipment connected to the HLU or HRU
Generic Loopback Commands
The HiGain Generic Loopback (GNLB) commands allow you to use inband codes to loop up either NLOC
(4-in-7) or NREM (3-in-7) towards the network. In addition, these inband codes loop up CREM (6-in-7) or CLOC
(5-in-7) towards the customer. Either loop-up condition can be terminated (looped down) with the 3-in-5 SMJK
loop-down code. All inband codes must be present for 5 seconds before the HiGain system responds. HiGain also
supports NDUx doubler loopbacks toward the network and CDUx doubler loopbacks toward the customer.
Figure 25 summarizes the available loopbacks in the system, and Table 14 on page 45 summarizes the HiGain
generic loopback commands. See “GNLB Test Procedures” on page 48 for the test procedures that apply when
using the GNLB mode.
Figure 25. Loopback Summary