Section 150-319-124
Revision 03
Page 15
14.02
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, which are shown in Table 1 and Figure 11
(non-doubler applications). The non-doubler loopback
locations are shown in Figure 6.
14.03
“GNLB” is the HiGain system Generic
Loopback code. The GNLB allows in-band codes to
loop up either the HLU/NLOC (4 in 7) or the
HRU/NREM (3 in 7) toward the network. In addition, it
allows in-band codes to loop up the HLU/CREM (6 in
7) or the HRU/CLOC (5 in 7) toward the customer.
Either loop-up condition is terminated (looped down)
with the (3 in 5) loop-down code. Both in-band codes
must be present for 5 seconds before the HiGain
system responds. Table 2 lists the test procedures
that apply when using the GNLB mode.
14.04
The A1LB loopback selection complies with
that proposed for HDSL systems in the T1E1.4/92
recommendation with the following additions (see
Table 3):
•
Query loopback
•
Intelligent Office Repeater (IOR) power-
down
•
Three loopback time-out choices
•
Initiation from either end
•
Repeating bit error signatures
•
Alternate query loopback
These additions make A1LB identical to A2LB, but
they retain separate identities to allow future T1/E1
enhancements to A1LB without affecting A2LB.
14.05
A2LB through A5LB are four special
addressable repeater loopback functions, which are
supported by the List 2D version of the HiGain
system. These loopbacks provide the HiGain system
with sophisticated maintenance and troubleshooting
tools. Table 4 through Table 7 list the details of these
SPLB functions. A2LB and A5LB are patterned after
the Teltrend addressable T1 repeater loopbacks.
A3LB and A4LB are patterned after the Wescom
addressable T1 repeater loopbacks. All 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)
14.06
A5LB differs from A2LB in that A5LB does not
block the arming (3 in 5) code from exiting the HLU-
319, List 2D into the network. A2LB can be
configured to either block this arming code after two
seconds and replace it with the AIS code or unblock it
by executing the Far-End Activate code. Since A5LB
never blocks the arming code from exiting the HLU-
319, List 2D, 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.
Refer to the PairGain HiGain-2 Intelligent Repeater
Application Note #910 Part #325-910-100 for more
SPLB details.
14.07
When T1 loopback tests are performed on the
HiGain system with metallic loopback connections at
either end, the T1 code, which exists at the metallic
loopback interface, may be different from the T1 code
being received at the opposite end when the DS1 user
code is set to Auto. This is caused by the fact that, in
the Auto DS1 code mode, the HLU-319, List 2D and
HRU-412 set their own codes independently of each
other. Each end sets its transmit code to match its
receive code. Thus, if one end is receiving AMI, and
the other B8ZS, their codes are different. For
example, if the HRU-412 has a metallic loopback, and
the HLU-319, List 2D receive pattern code is changed
from AMI to B8ZS, and next, the all “0” pattern is sent
into the HLU-319, List 2D, then the HLU-319, List 2D
changes to its B8ZS mode while the HRU-412
remains in its AMI mode, and thus loops all “0.” This
causes the HRU-412 to indicate an LOS condition,
which causes the HLU-319, List 2D to output the AIS
pattern.
14.08
The HiGain system may take longer than
normal to respond to in-band loopback commands
when its framing mode is set to UNFR and the in-band
commands are sent in either an SF or ESF mode.
The frame bits override the command bits and cause
errors in the command sequence. These errors cause
the HiGain system to reject some sequences. This
can extend the detection interval.
