CopperOptics PairGain HiGain-2 HRU-612 Manual - Page 9
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Print Page10. LOOPBACKS
10.01
Figure 5 shows all 4 HRU loopbacks. Of
these, a TLOS and CLOC are logic
loopbacks. They occur in the digital multiplexer
section of the HRU as shown in Figure 2.
10.02
Both the SMART-JACK and NREM
loopbacks shown in Figure 5 execute the
standard NID metallic loopback. The only difference
is their initiating sequence. NREM is initiated by the
HRV front panel pushbutton, the maintenance
terminal, the HLU front panel pushbuttons or the 3 in
7 in band commands. The SMART-JACK loopback
is only initiated by the standard 3 in 5 in band loop-up
command. It has two modes of operation as
determined by the two states (ENA or DIS) of the
SAIS user option. The ENA option causes the HRU
to transmit the AIS signal towards the NI. The DIS
option turns off this AIS/NI signal.
10.03
ENA: Upon detection of a valid SMART-
JACK loopback command, a metallic
loopback relay (see Figure 2 for its location) is
energized and the T1 interface chip transmits the
AIS pattern to the NI and also back to the HRU's T1
receiver circuit. In addition, the customer's T1 XMT
input is disconnected and terminated into 100 ohms.
The AIS pattern is examined by the HRU for its
overall integrity. This pre-looped tests lasts for about
100 milliseconds and terminates in one of the
following two conditions:
A, PRE-LOOP FAILED: If the transmit & receive all
1's patterns do not match, a problem in the HRU is
indicated and HiGain-2 declares an HRU PRE-
LOOPBACK FAIL condition. This terminates the
loopback test and returns the HRU to its unlooped
normal state. Note that other circuit impairments
could also prevent the loopback from occurring.
B, PRE-LOOP PASSED:- If the transmit and receive
patterns do match, a HRU PRE LOOPBACK PASS
condition is declared. All active circuits are working.
The metallic loopback relay remains closed and, in
addition, a logic loopback within the HRU is enabled.
This logic loopback is required in order to present
the all 1's pattern to the NI and at the same time to
loop the signal, being received from the network,
back towards the network. HiGain-2 is now in its
AIS/ENA "smart-jack" loopback state. It remains in
this state until a loopdown command is detected or
the default time out period (if enabled) expires.
10.04
When the HRU is in its AIS/ENA smart-jack
metallic loop back state, its T1 input LOS,
Code & 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 ohms. This forces the FRM LED off, the LOC
LOS LED off and the CODE LED to indicate AMI if
the HLU CODE option is set to either AUTO or AMI.
It will indicate B8ZS if the CODE option is set to
B8ZS.
10.05
As can be seen, this AIS/ENA metallic
loopback scenario includes and therefore
tests all HiGain-2 active circuits and fully conforms
with TR-TSY-000312. In this sense it out performs
the loopback function found in most standard NID
devices since these devices do not include either the
AIS generator or the CI T1 LOS detector in their
loopback path.
10.06
DIS: This metallic loopback state is initiated
in the same manner as it is when the ENA
option is chosen. However, once initiated, the AIS
signal is not sent to the NI. Instead the network
signal is sent both towards the NI and through the
relay back towards the network. As before, the
customer's T1 transmit input port is opened and
terminated into 100 ohms. No logic loopback is
required since the relay is performing the network
signal loopback function. This simple metallic
loopback state remains until a loopdown command is
issued or the default timer (if enabled) expires.
10.07
When the HRU is in its AIS/DIS smart-jack
metallic loop back state, its T1 input LOS,
Code & Frame monitoring circuits are connected to
the network's signal 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 ohms. The FRM & LOC LOS LEDs indicate the
status of this signal from the network. The CODE
LED also indicates the code (AMI or B8ZS) of this
signal if the CODE option is set to AUTO. It will
indicate AMI or B8ZS if the CODE option is set to
either AMI or B8ZS respectively.
10.08
The user should be aware that this AIS/DIS
smart-jack mode does not check all of the
HRU's circuits nor does it send an AIS alerting signal
to the NI. Thus it does not comply with TR-312
requirement to transmit the AIS pattern to the CI
during the maintenance loopback state.
Section 150-612-100
Revision 02
Page 9