Testing LTPH-UM-1049-02, Issue 2
56 January 9, 2002 H2TU-C-319 List 4E
Generic Loopback Commands
The HiGain HDSL2 Generic Loopback (GNLB) commands allow you to use in-band codes to loop up either
NLOC (4-in-7) or NREM (3-in-7) towards the network. In addition, these in-band 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 in-band codes must be present for at least 5 seconds before the HiGain HDSL2 system
responds. TLOS is a logic loopback caused by loss of the DS1 input from the CI.
Figure31 on page 55 summarizes the available loopbacks in the system, and Table22 on page56 summarizes the
HiGain HDSL2 generic loopback commands. See “GNLB Test Procedures” on page59 for the test procedures
that apply when using the GNLB mode.
Special Loopback Commands
In addition to the GNLB loopback command mode, a HiGain HDSL2 system can be configured for one of three
special loopback command modes. These are selected from the maintenance terminal Config menu, ADC Options
screen (see Table5 on page 18) or by using the MODE and LBK pushbuttons (see Figure 32 on page60). Once a
loopback mode is activated, other loopback commands can be sent by a test set connected to the craft port of the
H2TU-C or H2TU-R (see Table22 on page 56 and Table 24 on page64 for list of SPLB commands).
A2LB through A4LB are special, addressable, repeater loopback modes that are supported by the H2TU-C. These
loopback modes provide the HiGain HDSL2 system with sophisticated maintenance and troubleshooting tools.
A2LB is patterned after the Teltrend addressable T1 repeater loopbacks. A3LB and A4LB are patterned after the
Wescom addressable T1 repeater loopbacks.
All three SPLBs have been enhanced to handle the specific requirements of the following HiGain HDSL2
customers:
•A2LB (Teltrend) = Southwestern Bell
•A3LB (Wescom) = New England Telephone, Bell Atlantic
•A4LB (Wescom Mod 1) = New York Telephone
A2LB can be configured to do one of the following:
•Block the arming code (after 2 seconds) from exiting the H2TU-C into the network, and replace it with the
AIS code.
•Unblock the AIS code by executing the Far-End Activate code.
A3LB and A4LB are identical because all of the SMJK loopup and loopdown commands are under control of the
LPBK setting.
Table 22. Summary of HiGain HDSL2 Generic Loopback Codes and Activation Methods
Method of Activation
Loopback Code Description Test Set Craft Port MODE/LBK
NLOC 1111000
4-in-7
DSX-1 signal is looped back to the network at the H2TU-C. X X X
NREM 1110000
3-in-7
DSX-1 signal is looped back to the network at the H2TU -R. X X X
CLOC 1111100
5-in-7
Signal from the customer is looped back to the customer
at the H2TU-R. X X X
CREM 1111110
6-in-7
Signal from the customer is looped back to the customer
at the H2TU-C. X X X