
150-231-184-05, Revision 05
Troubleshooting
HLU-231 List 8D
October 25, 1999
43
A5LB Loopback Commands
A5LB is a specific, addressable, repeater loopback mode which is supported by the HLU-231 List 8D. This
loopback mode provides the HiGain system with sophisticated maintenance and troubleshooting tools. The A5LB
is patterned after the Teltrend Mod 1 addressable T1 repeater loopbacks and has been enhanced to handle the
specific requirements of the following HiGain customers:
•
Southern New England Telephone (SNET)
•
Southwestern Bell
•
Pacific Bell.
The A5LB 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) powerdown
•
Four loopback time-out choices
•
Initiation from either end
•
Repeating bit error signatures
•
Alternate query loopback.
A5LB blocks the arming code from exiting the HLU-231 into the network. By arming the system from the remote
unit, the A5LB 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.)
Manual Loopback Session
A manual loopback session allows you to select any one of the HiGain A5LB loopbacks listed in
with the exception of SmartJack loopbacks, which can only be issued by inband commands.
Setting the Loopback Time-out Option
Before initiating a loopback session, verify that the Loopback Time-out parameter is set to the desired setting.
1
Use the MODE and SEL buttons as described in
“Setting Options through MODE and SEL” on page 11
.
(The Loopback Time-out parameter is also user-selectable from the System Settings screen when using a
maintenance terminal.)
2
Enter the desired setting:
a
NONE (no time-out)
b
20 minutes
c
60 minutes
d
120 minutes (default setting).
A HiGain system may be delayed in responding to inband loopback commands when the
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.