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Loopbacks
S
J
MART
ACK
The SmartJack loopback shown in
loopback. It has two modes of operation as determined by the SAIS user
option settings at the HLU (ENA or DIS). The ENA option causes the HRU
to transmit the AIS signal towards the NI. The DIS option turns off the
AIS/NI signal. To send the AIS pattern to the CI during SmartJack or NREM
loopbacks, set the SAIS to ENA.
SAIS S
ET TO
Upon detection of a valid SmartJack loopback command, a metallic loopback
relay (see
Figure 22 on page
transmits the AIS pattern to the NI and also back to the HRU-419 T1 receiver
circuit. In addition, the customer's T1 XMT input is disconnected and
terminated into 100 Ω. The AIS pattern is examined by the HRU for its overall
integrity. This pre-looped test lasts for about 100 ms and terminates in one of
the following two conditions:
•
Pre-loop Failed - If the transmit and receive all ones patterns do not
match, there is a problem in the HRUand an HRU Pre-Loopback Fail
condition occurs. This terminates the loopback test and returns the HRU
to its unlooped normal state. This indicates a defective HRU.
•
Pre-loop Passed - If the transmit and receive patterns do match, the
system declares an HRU Pre-loop Passed condition. All active circuits
are working. The metallic loopback relay remains closed and, in
addition, enables a logic loopback within the HRU. This logic loopback
is required in order to present the all ones pattern to the NI and at the
same time to loop the signal being received from the network back
towards the network. This places the HiGain system in its AIS/ENA
SmartJack loopback state. It remains in this state until a loopdown
command is detected or the default time out period (if enabled) expires.
When the HRU is in its AIS/ENA SmartJack metallic loop back state, its T1
input LOS, Code and Frame monitoring circuits are connected to the
unframed AIS pattern which is being looped back to these circuits through the
loopback relay. The CPE input signal is no longer being monitored since its
input circuit has been opened and terminated into 100 Ω. This forces the FRM
LED off, the LOC LOS LED off and the Code LED to indicate AMI if the
44
(SMJK) L
OOPBACK
Figure 21
ENA
50) is energized and the T1 interface chip
September 25, 1998
150-419-100-03>
is the standard NID metallic
HRU-419 List 1
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