150-432-100-02, Revision 02
Troubleshooting
HLU-432 List 1
July 18, 2002
43
Special Loopback Commands
In addition to the GNLB loopback command mode, a HiGain system can be configured for one of five special
loopback command modes. These are selected from the maintenance terminal System Settings screen (see
) or by using the MODE and SEL buttons (see
). Once a loopback mode is
activated, other loopback commands can be sent by a test set connected to the craft port of the HLU or HRU (see
and
for list of SPLB commands).
A1LB through A5LB are five special, addressable, repeater loopback modes which are supported by the HLU-432
List 1. These loopback modes provide the HiGain system with sophisticated maintenance and troubleshooting
tools. A1LB, 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 five SPLBs have been enhanced to
handle the specific requirements of the following HiGain customers:
•
A1LB (Teltrend) = Southwestern Bell
•
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), Southwestern Bell, Pacific Bell
The A1LB loopback selection complies with that proposed for HDSL systems in the T1E1.4/92 recommendation
with the following additions:
•
query loopback
•
IOR (Intelligent Office Repeater) power-down
•
four loopback time-out choices
•
initiation from either end
•
repeating bit error signatures
•
alternate query loopback
These additions make A1LB identical to A2LB. A1LB is given a separate identity to allow future T1/E1
enhancements to be added without affecting A2LB.
A5LB differs from A2LB in that A5LB does not block the arming code from exiting the HLU-432 into the
network. A2LB can be configured to do one of the following:
•
block the arming code (after 2 seconds) from exiting the HLU into the network and replace it with the AIS
code.
•
unblock the AIS code by executing the Far-End Activate code. (Since A5LB never blocks the arming code
from exiting the HLU, the Far-End Activate code is not available in A5LB.)
A3LB differs from A4LB in that A3LB supports the additional (1-in-6) SMJK loopback command.
A HiGain system may take longer than normal to respond to inband loopback commands when
its framing mode is set to UNFR and the inband commands are set in either 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.
