Section 150-388-124
Revision 01
Page 38
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-388, 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-388,
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-388, 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
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 paragraph 19.10
below for front panel-initiated loopbacks.) The simplest
HiGain system includes two loopback locations: the HLU-
388, List 2D and the HRU-412. The most complex HiGain
system application includes the HLU-388, List 2D, HRU-
412 and two in-line 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-388, 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-388, List 2D receive pattern code is
first changed from AMI to B8ZS, and next, the all “0”
pattern is sent into the HLU-388, List 2D, then the HLU-
388, 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-388, List 2D to
output the AIS pattern.
19.09
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.
