Section 150-231-164
Revision 04
Page 34
3.04
The A1LB loopback selection (Table 14)
complies with that proposed for HDSL systems
in the T1/E-1.4/92 recommendation with the following
additions:
•
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
described below. It is given a separate identity to allow
future T1/E1 enhancements to be added without
affecting A2LB.
3.05
A2LB through A5LB are four special address
-able repeater loopback functions which are
supported by the HLU-231 List 6D HiGain system.
These loopbacks provide the HiGain system with
sophisticated maintenance and trouble shooting tools.
Table 15 through Table 18 list the details of these SPLB
functions. A2LB & A5LB are patterned after the Teltrend
addressable T1 repeater loopbacks. A3LB & 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)
3.06
A5LB differs from A2LB in that A5LB does not
block the arming code from exiting the HLU-231
List 6D into the network. A2LB can be configured to
either block this arming code after two seconds, and
replace it with the AIS code, or to unblock it by executing
the FAR-END ACTIVATE code. Since A5LB never
blocks the arming code from exiting the HLU-231 List
6D, 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.
3.07
Two additional loopback points are added for
each HDU-451 doubler that is used as shown in
Figure 14. NDU1 and NDU2 are executed towards the
network. CDU1 and CDU2 are towards the customer.
All four loopbacks can be initiated by the 16 bit in-band
commands in SPLB states A1LB, A2LB & A3LB as
described in Tables: Table 14, Table 15, & Table 16
respectively. NDU1 and NDU2, along with the rest of
the loopbacks towards the network, can be issued from
the Loopback Menu shown in Figure 22. See Section C
paragraph 3.10 below for Front Panel-initiated
loopbacks. The simplest HiGain system includes two
loopback locations: The HLU-231 List 6D and the HRU-
412. The most complex HiGain system application
includes the HLU-231 List 6D, HRU-412 & two in-line
HDU-451 Doublers. Refer to the PairGain HiGain
Intelligent Repeater Application Note # 910, Part # 325-
910-100, for more SPLB details.
3.08
When T1 loopback tests are performed on the
HiGain system with metallic loopback
connections at either end, the DS1 code that exists at
the metallic loopback interface may be different from the
DS1 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-231 List
6D & HRU-412 set their own code independent 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-231
List 6D receive pattern code is first changed from AMI to
B8ZS, and second, the all “0” pattern is sent into the
HLU-231 List 6D, the HLU-231 List 6D 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 a LOS condition, which
then causes the HLU-231 List 6D to output the AIS
pattern.
3.09
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.
