150-431-115-01, Revision 01
Loopback Operation
HLU-431 List 1E
September 22, 1998
37
A2LB through A5LB are four special, addressable, repeater loopback functions which are supported by the
HLU-431 List 1E. These loopbacks provide the HiGain system with sophisticated maintenance and trouble
shooting tools. 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)
A5LB differs from A2LB in that A5LB does not block the arming code from exiting the HLU-431 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 Line Unit, it does not need this FAR-END ACTIVATE code. 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 in-band loopback commands when its framing mode
is set to UNFR and the in-band commands are set 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.
I
NITIATING
M
ANUAL
L
OOPBACK
S
ESSIONS
A manual loopback session allows you to select one of four HiGain system loopbacks.
To initiate a manual loopback session:
1
Press both the MODE and SEL buttons on the front panel for at least 3 seconds. The following message
appears on the front panel display:
MAN LPBK
followed by the message:
NLO?
Any of the HiGain loopbacks can be executed using the MODE and SEL buttons.
In general, to execute a manual loopback session using the MODE and SEL buttons:
•
The next loopback option can be presented by pressing the MODE button, however, the
previously executed loopback remains active until the SEL button is pressed and a different
loopback is activated.
•
If neither button is pressed for a period of 30 seconds and no loopback is in effect, the
manual loopback session terminates and the normal margin displays reappear.
•
If any loopback is in effect, the 30-second timeout is inhibited. The active loopback and the
manual loopback session continue until the loopback times out in accordance with the
LBTO setting.
•
Only the SMJK loopback can exist with other networks at any given time.
•
Pressing both buttons, again for 3 seconds, terminates any active loopback, ends the
Manual loopback session and returns the display to normal mode.
