PairGain HiGain HLU-431 1E, Руководство пользователя, Страница: 46 / 68

Loopback Operation 150-431-115-01, Revision 01
36 September 22, 1998 HLU-431 List 1E
S
ELF
T
EST
The Self Test mode that occurs when both HDSL loops are not in sync has been enhanced to include the input
DS1 transceiver chip. The Self Test procedure can cause the AIS pattern that is normally transmitted from the
HLU-431 during these out of sync intervals, to exhibit occasional BPVs.
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, Table 14 , 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.
A
DDRESSABLE
R
EPEATER
L
OOPBACK
F
UNCTIONS
In addition to the SMJK loopback, a HiGain system can be configured for one of five special in-band loopback
(SPLB) command sequences. These are selected from the SPLB user option shown in
Table 9 on page 24 and
Figure 21 on page 39 (non-doubler applications). Doubler loopback locations are shown in Figure 22 on page 40 .