Issue 1, Section 150-231-134
Revision 01
Page 13
10. LOOPBACK DESIGN DESCRIPTION
10.01
The HiGain family of loopbacks is shown in
Figure 4. The most important of these is the
Smart Jack loopback. It is enabled by the LPBK user
option. It configures the HRU-412 to respond to the
standard NIU 2/3 in 5 in-band loopback codes. It
should be enabled when the HRU is used to replace
an external NIU.
10.02
In addition to the SmartJack loopback, HiGain
can be configured for one of five special in-
band loopback command sequences. These are
selected from the SPLB user option shown in Figure
14.
10.03
GNLB is the HiGain Generic loopback code.
The GNLB 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 CDU2 (5 in 6). Either loop-up condition is
terminated (looped-down) with the 3 in 5 loop-down
code. All messages must be present for five seconds
before HiGain responds. Table 4 lists the test
procedures that apply when using the GNLB mode.
10.04
The A1LB loopback selection (Table 5)
complies with that proposed for HDSL
systems in the T-1/E-1.4/92 recommendation with the
following additions:
1) Query loopback
2) IOR powerdown
3) Three loopback time-out choices
4) Initiation from either end
5) Repeating bit error signatures
6) Alternate Query loopback
These additions make A1LB identical to A2LB
described below. It is given a separate identity to
allow future T-1/E-1 enhancements to be added
without affecting A2LB.
Figure 4. HLU-231, List 3D Loopback Configurations. The most important of the HiGain family of loopback options is the
Smart-Jack loopback, which emulates the functions of a standard NID.
