Section 150-232-100
Revision 01
Page 23
3. LOOPBACK OPERATION
3.01 The HiGain system has a family of loopback options. The most important of these is the “Smart-Jack”
loopback which enables the HRU-412 to respond to the standard (2/3 in 5) Smart-Jack in-band loopback codes and
thus emulate the functions of a standard Network Interface Device (NID). This option can be enabled or disabled
from either the front panel buttons or the terminal SYSTEM SETTINGS MENU.
3.02 In addition to the Smart-Jack loopback, the HiGain system can be configured for one of five special in-band
loopback (“SPLB”) command sequences. These are selected from the SPLB user option shown in Table 2 and
Figure 16 (non-Doubler applications). The non-Doubler loopback locations are shown in Figure 6.
3.03 “GNLB” is the HiGain system Generic loopback code. The “GNLB” option allows in-band codes to loop-up
either the HLU/NLOC (4 in 7) or HRU/NREM (3 in 7) towards the network. In addition, it allows in-band codes to
loop-up the HLU/CREM (6 in 7) or HRU/CLOC (5 in 7) towards the customer. Either loop-up condition is terminated
(looped-down) with the 3 in 5 loop-down code. All the in-band loop codes must be present for at least 5 seconds
before the HiGain system responds. Table 4 lists the test procedures that apply when using the “GNLB” mode.
3.04 The A1LB loopback selection, Table 5, complies with that proposed for HDSL systems in the T1E1.4/92
recommendation with the following additions:
♦
Query loopback
♦
IOR (Intelligent Office Repeater) power-down
♦
Three loopback time-out choices
♦
Initiation from either end
♦
Repeater bit error signatures
♦
Alternate query loopback
These additions make A1LB identical to A2LB described on the following page. It is given a separate identity to
allow future T1/E1 enhancements to be added without affecting A2LB.
3.05 A2LB through A5LB are four special addressable repeater loopback functions which are supported by the
HiGain System. These loopbacks provide the HiGain system with sophisticated maintenance and trouble shooting
tools. Table 6 through Table 9 list the details of these “SPLB” functions. A2LB & A5LB are patterned after the
Teltrend addressable T1 repeater loopbacks. A3LB & A4LB are patterned after the Wescom addressable T1
repeater loopbacks. The following four SPLBs have been enhanced to handle the specific requirements of the
following HiGain system customers:
♦
A2LB (Teltrend) = Southwestern Bell
♦
A3LB (Wescom) = New England Telephone
♦
A4LB (Wescom Mod 1) = New York Telephone
♦
A5LB (Teltrend Mod 1) = Southern New England Telephone (SNET)
3.06 A5LB differs from A2LB in that A5LB does not block the arming code from exiting the HLU-232 List 1D into the
network. A2LB can be configured to either block this arming code after two seconds, and replace it with the AIS
code, or to unblock it by executing the FAR-END ACTIVATE code. Since A5LB never blocks the arming code from
exiting the HLU-232 List 1D, it does not need this FAR-END ACTIVATE code. A3LB differs from A4LB in that A3LB
supports the additional (1 in 6) Smart-Jack loopback command.
