Section 150-619-100
Revision 01
Page 12
9. LOOPBACK OPERATION
9.01
HiGain-2 has several of loopback options.
The most important is the “Smart-Jack” loopback,
which allows the HRU-612 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 RS-232
terminal System Settings Menu.
9.02
In addition to the Smart-Jack loopback, the
HiGain-2 can be configured for one of five special in-
band loopback command sequences. These are
selected from the SPLB user options, shown in the
GNLB Test Procedure and Figure 9 of the next
section. The loopback locations are shown in Figure
5.
9.03
“GNLB” is the HiGain-2 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-2 system responds.
9.04
The A1LB loopback selection complies with
that proposed for VHDSL systems in the T1E1.4/92
recommendation with the following:
•
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
(described below), but they retain separate identities
to allow future T1E1 enhancements to A1LB without
affecting A2LB.
9.05
A2LB through A5LB are four special
addressable repeater loopback functions. These
loopbacks provide HiGain-2 with sophisticated
maintenance and troubleshooting tools list the
details of these Special Loopback (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-2 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)
9.06
A5LB differs from A2LB in that A5LB does
not block the arming (3 in 5) code from exiting the
HLU-619 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-
619, it does not need this Far-End Activate code.
A3LB differs from A4LB in that A3LB supports the
additional Smart-Jack loopback (1 in 6) command.
Refer to the PairGain HiGain-2 Intelligent Repeater
Application Note #910 Part #325-910-100 for more
SPLB details.
9.07
When T1 loopback tests are performed on
the HiGain-2 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 occurs
because in the Auto DS1 code mode, the HLU-619
and HRU-612 set their own codes independently of
each other. Each end sets its transmit code to
match its receive code. So, if one end is receiving
AMI, and the other B8ZS, their codes are different.
For example, if the HRU-612 has a metallic
loopback, and the HLU-619 receive pattern code is
changed from AMI to B8ZS, and next, the all “0”
pattern is sent into the HLU-619, then the HLU-619
changes to its B8ZS mode while the HRU-612
remains in its AMI mode, and thus loops all “0.” This
causes the HRU-612 to indicate an LOS condition,
which causes the HLU-619 to output the AIS
pattern.
