152-388-100-02, Issue 2 Testing
H2TU-C-388 List 1 June 6, 2000 39
LOOPBACK OPERATION
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 allows you to verify the integrity of the HDSL2 channels
to the H2TU-C, the H2TU-C DSX-1 interface, and the DS1 channels to the customer. Loopback options include:
• Generic Loopback (GNLB) options, including the SmartJack (SMJK) option (see Table 15 on page 40)
• Special Loopback (SPLB) options (see “Special Loopback Commands” on page 41) and the following
command tables:
– Addressable Repeater Loopback commands: A1LB, A2LB, A5LB (see Table 16 on page 45)
– Addressable Repeater Loopback commands: A3LB, A4LB (see Table 17 on page 47)
Loopback commands can be initiated by:
• Selecting the loopback type using the MODE and SEL buttons on the H2TU-C front panel (or the Manual
Loopback button on the H2TU-R)
• Selecting the loopback type from the Monitor Menu when connected to the craft port of the H2TU-C or
H2TU-R
• Entering the loopback code (exceptions are COLB, DxLB, and RULB) into the test equipment connected to
the H2TU-C or H2TU-R
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 loopup condition can be terminated (looped down) with the 3-in-5, SMJK
loopdown code. All inband codes must be present for at least 5 seconds before the HiGain system responds. TLOS
is a logic loopback caused by loss of the DS1 input from the CI.
Figure 26 summarizes the available loopbacks in the system, and Table 15 on page 40 summarizes the HiGain
generic loopback commands. See “GNLB Test Procedures” on page 43 for the test procedures that apply when
using the GNLB mode.
Figure 26. Loopback Summary
HiGain supports multiple loopbacks, but a single loopback is the preferred method.
Network
Customer
Premises
Activate loopback using
one of the following:
• MODE/SEL pushbuttons
• MaintenanceTerminal
•Test Set
Activate loopback using
one of the following:
• LBK pushbutton
• MaintenanceTerminal
•Test Set
H2TU-C H2TU-R
NLOC
NREM
SMJK
TLOS
CREM CLOC
