Loopback Operation
150-231-175-01, Revision 01
38
September 23, 1998
HLU-231 List 7E
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?
2
Do one of the following:
•
To execute an NLOC loopback, press the SEL button. The message changes from
NLO?
to
NLOC
.
•
To execute an NREM loopback:
–
Press the MODE button. The message changes from
NLO?
to
NRE?
–
Press the SEL button to execute the NREM loopback.
3
To execute a CRE loopback, press the MODE button again.
4
To execute a CLO loopback, press the MODE button a third time.
These same loopbacks can be initiated from the RS-232 Craft port by choosing the Loopback Mode, option D,
from the Main Menu. This displays the Loopback Menu (
) from which any of the loopbacks
can be initiated or terminated.
All loopbacks, except the SMJK loopback, can be initiated by either in-band commands in the T1 payload or by
a command from HiGain itself (front panel buttons or maintenance screen selections). Thus, whenever a loopback
is active, the method by which it was activated is indicated in the Loopback and Status screens by inserting either
HG (HiGain) or PL (Payload) adjacent to the identified loopback, for example NREM(HG).
L
OOPBACK
T
EST
P
ROCEDURES
The following sections provide step-by-step test procedures for the HLU-231 as a function of the loopback option
selected. These procedures allow verification of the integrity of the HDSL channels at every module location as
well as the DS1 channels to the customer and the local DSX-1 interface.
If trouble is encountered on the HLU-231 DSX-1 interface, verify that the HLU is making a positive connection
with its mounting assembly (shelf) connector. Also, verify that the HLU internal equalizer is set to the correct
distance range. All equalizers should be set to the distance from the DSX-1 to the shelf.
The transmit and receive T1 DSX-1 ports have splitting access jacks and miniature, 210-series, bridging jacks as
shown in
. Connecting one cable between the two bridging jacks and another between the two
SPAN jacks splits the XMT and RCV and creates metallic loopbacks towards both the DSX-1 and the HLU-231.
If separate plugs are inserted into both SPAN jacks with the other end disconnected, the BRG jacks can be used
to send and receive test patterns towards the DSX-1.
