Section 150-319-124
Revision 03
Page 39
19.03
“GNLB” is the HiGain system Generic
Loopback code. The GNLB allows in-band codes
from the network 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 from the Network
Interface (NI) to loop up the HLU/CREM (6 in 7) or the
HRU/CLOC (5 in 7) toward the customer. For doubler
applications, it permits looping doubler number 1
toward the network NDU1 (2 in 6) or toward the
customer CDU1 (4 in 6). Doubler number 2 is looped
toward the network with NDU2 (3 in 6) or toward the
customer with 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 the HiGain system will respond.
Table 12 lists the test procedures that apply when
using the GNLB mode.
19.04
The A1LB loopback selection complies with
that proposed for HDSL systems in the T1/E-1.4/92
recommendation with the following additions (see
Table 13):
•
Query loopback
•
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 the A2LB, but
they retain separate identities to allow future T1/E1
enhancements to A1LB without affecting A2LB.
19.05
A2LB through A5LB are four special
addressable repeater loopback functions, which are
supported by the HLU-319, List 2D HiGain system.
These loopbacks provide the HiGain system with
sophisticated maintenance and troubleshooting tools.
Table 14 through Table 17 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)
19.06
A5LB differs from A2LB in that A5LB does not
block the arming 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.
19.07
Two additional loopback points are added for
each HDU-451 doubler that is used, as shown in
Figure 15. NDU1 and NDU2 are executed toward the
network. CDU1 and CDU2 are toward the customer.
All four loopbacks can be initiated by the 16-bit in-
band commands in SPLB states A1LB, A2LB and
A3LB as described in Tables 13, 14, and 15
respectively. NDU1 and NDU2, along with the rest of
the loopbacks toward the network, can be issued from
the Loopback Menu shown in Figure 23. (See Section
C Paragraph 19.10 below for front panel-initiated
loopbacks.) The simplest HiGain system includes two
loopback locations: the HLU-319, List 2D and the
HRU-412. The most complex HiGain system
application includes the HLU-319, List 2D, HRU-412
and two in-line HDU-451 doublers. Refer to the
PairGain HiGain Intelligent Repeater Application Note
#910, Part #325-910-100, for more SPLB details.
19.08
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 first
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
back the all “0” pattern. This causes the HRU-412 to
indicate an LOS condition, which then causes the
HLU-319, List 2D to output the AIS pattern.
