Installation
150-512-100-03, Revision 03
26
September 25, 1998
HRU-512 List 1
NAIS-DIS
When the HRU is in the NAIS-ENA (enabled) loopback state, the HRUs DS1
input LOS, Code, and Frame monitoring circuits are connected to the signal
being received from the CPE. Thus the HRUs front panel CODE and FRM
LEDs indicate the status of the customer’s DS1 input signal.
When the NAIS option is set to DIS, the AIS signal is not transmitted to the
CPE. Instead, the HRUs DS1 output signal is disconnected (opened) from the
CPE and terminated into a 100 ohm termination. This causes an LOS signal
condition to be transmitted from the HRUs DS1 output port towards the CPE
which in turn alerts customer maintenance personnel of the circuit’s off-line
condition. In addition, the HRUs DS1 input port is also disconnected and
terminated into 100
Ω
. At the same time a metallic relay is activated which
loops the NI signal back towards the network. The Hi Gain system is now in
the NAIS-DIS metallic 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.
When the HRU-512 List 1 is in the NAIS-DIS metallic loopback state, the
HRUs DS1 input LOS, Code, and Frame monitoring circuits are connected to
the network’s signal which is being looped back to these circuits through the
metallic loopback relay. The CPE input signal is no longer being monitored
since its input circuit has been opened and terminated into 100
Ω
. The FRM
LED indicates the framing pattern of the network signal. The LOC LOS LED
will always be OFF. The CODE LED will indicate AMI or B8ZS if the CODE
option is set to either AMI or B8ZS respectively. However, the CODE LED
state is indeterminate if the CODE option is set to AUTO.
The HRU-512 List 1 front panel pushbuttons can also be used to terminate
any NREM loopback irrespective of how it was initiated.
The HLU can be looped up (CREM) from the HRU-512 List 1 DS1 interface
with a Full T1 6-in-7 in-band command. The HRU-512 List 1 itself can be
looped up (CLOC) from the HRU-512 List 1 DS1 interface with a Full T1
5-in-7 in-band command. Both command patterns must be full 24-channel T1
signals that must last for at least 5 seconds, and may be either framed or
unframed. The loop down command for both is the standard Full T1 3-in-5
(5 second) pattern.
The complete family of FT1 loopbacks (CLOC, CREM, NLOC and NREM)
are detailed in the HLU FT1 HiGain Line Unit Technical Practice, that can be
referenced to obtain a thorough understanding of the loopbacks available in
this FT1 system and how the loopbacks differ in operation from a normal full
T1 system.
