Section 150-232-100
Revision 01
Page 51
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. This option
can be enabled or disabled from either the front panel settings or the terminal SYSTEM SETTINGS Menu Screen.
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 options shown in Table 2. The
loopback locations are shown in Figure 27.
3.03 “GNLB” is the HiGain system Generic loopback code. The “GNLB” option allows in-band codes from the
network 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 from the Network Interface (NI) to loop-up the HLU/CREM (6 in 7) or HRU/CLOC (5 in 7) towards the
customer. For Doubler applications it permits looping Doubler #1 towards the network NDU1 (2 in 6) or towards the
customer CDU1 (4 in 6). Doubler #2 is looped towards the network with NDU2 (3 in 6) or towards the customer with
CDU2 (5 in 6). Either loop-up condition is terminated (looped-down) with the (3 in 5) loop-down code. All in-band
loop codes must be present for at least five seconds before the HiGain system will respond. Table 16 lists the test
procedures that apply when using the “GNLB” mode.
3.04 The A1LB loopback selection (Table 17) complies with that proposed for HDSL systems in the T1/E-1.4/92
recommendation with the following additions:
♦
Query loopback
♦
IOR power-down
♦
Three loopback time-out choices
♦
Initiation from either end
♦
Repeater bit error signatures
♦
Alternate query loopback.
These additions make A1LB identical to the A2LB described below. 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
HLU-232 List 1D HiGain system. These loopbacks provide the HiGain system with sophisticated maintenance and
trouble shooting tools. Table 16 through Table 21 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.
