Loopback Operation
150-231-175-01, Revision 01
36
September 23, 1998
HLU-231 List 7E
S
ELF
T
EST
When both HDSL loops lose sync word (LOSW), a minor alarm condition exists. Because the HLU-231 List 7E
enters a self test cycling mode, the front panel LED lights yellow instead of red and the “SELF TEST” message
is displayed instead of the “ALRM” message.
L
OOPBACK
O
PERATION
This section discusses loopback operations that are used to test the HiGain system.
S
MART
J
ACK
(SMJK) L
OOPBACK
One of the most important loopback options is the SmartJack (SMJK) loopback, which enables an HRU response
to the standard (2 and 3-in-5) SMJK in-band loopback codes in emulation of standard Network Interface Device
(NID) functions. This option can be enabled or disabled from either the front panel MODE and SEL buttons or
through the System Settings screen.
G
ENERIC
L
OOPBACK
C
ODE
(GNLB)
The HiGain generic loopback code is GNLB. The GNLB allows in-band codes to loop-up either the HLU/NLOC
(4-in-7) or HRU/NREM (3- in-7) towards the network. In addition, it allows in-band codes to loop-up the
HLU/CREM (6-in-7) or HRU/CLOC (5-in-7) towards the customer. Either loop-up condition is terminated
(looped-down) with the 3-in-5, loop-down code. Both in-band codes must be present for 5 seconds before the
HiGain system responds. See
“GNLB Loopback Test Procedures” on page 41
for the test procedures that apply
when using the GNLB mode.
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
•
Three loopback time-out choices
•
Initiation from either end
•
Repeating bit error signatures
•
Alternate query loopback
These additions make A1LB identical to A2LB described in the next section. It is given a separate identity to allow
future T1/E1 enhancements to be added without affecting A2LB.
