150-512-100-03, Revision 03
Installation
HRU-512 List 1
September 25, 1998
25
L
OOPBACKS
The HRU-512 List 1 supports 4 types of loopbacks (see Figure 6).
•
NREM (network remote loopback)
•
NLOC (network local loopback
)
•
CLOC (customer local loopback)
•
CREM (customer remote loopback
shows the two remote unit loopbacks NREM and
CLOC. NREM and CLOC can be initiated from the HLU front panel
pushbuttons or from a maintenance terminal attached to the HLU front panel
DB-9 Craft port. In addition, NREM can be initiated through the LB button
on the front panel of the HRU-512 List 1 and from an HLU DDS NEI in-band
DS0 latching loopback command. CLOC can also be initiated by a Full T1
5-in-7 in-band code at the HRU-512 List 1 DS1 input port. CLOC is a logic
loopback that occurs in the digital multiplexer function of the
HRU-512 List 1 as shown in the block diagram. (See
).
The NREM loopback (shown in
) is the standard NID metallic
loopback. NREM has two modes of operation depending on the setting (ENA
or DIS) of the NAIS user option at the HLU. The ENA option causes the
HRU-512 List 1 to transmit the AIS signal towards the CPE for all 24 time
slots (full T1 bandwidth). The DIS option turns off the AIS signal and causes
the HRU-512 List 1 to transmit LOS towards the CPE for all 24 time slots.
NAIS-ENA
Upon detection of the NREM loopback command (see
for its
location) the AIS signal is transmitted towards the CPE. In addition, a logic
loopback within the HRU is enabled and loops the NI signal back towards the
network. The HiGain system is now in the NAIS-ENA logic loopback state
and remains in this state until a loopdown command is detected from the
network or the user selected default time out period (if enabled) expires.
