150-402-102-01, Revision 01
Appendix A: Additional Technical Information
HRU-402 List 2
July 27, 1998
53
SAIS Set to ENA
Upon detection of a valid SmartJack loopback command, a metallic loopback
relay (see
) is energized and the T1 interface chip transmits the AIS
pattern to the NI and also back to the HRU-402 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
prelooped 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, a problem in the HRU is indicated and HiGain declares an HRU
PRE-LOOPBACK FAIL condition. 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 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 CPE and at the same time to
loop the signal being received from the network back towards the
network. This puts 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 Local (LOC) Loss (LOS) LED off and the Code LED to indicate
AMI if the HLU Code option is set to either AUTO or AMI. The HRU-402
List 2 LED indicates B8ZS if the Code option is set to B8ZS.
SAIS Set to DIS
This metallic loopback state is initiated in the same manner as when the ENA
option is chosen. However, once initiated, the AIS signal is not sent to the
CPE. Instead the network signal is sent through the relay back towards the
network, and the signal sent towards the NI is quiet. As before, the customer’s
T1 transmit input port is opened and terminated into 100
Ω
. No logic loopback
