Revision 01
June 12, 1997
Section 150-441-124
HiGain HLU-D41
PairGain Engineering - Plant Series
Page 39
24.2
Loopback Types (non-doubler applications)
24.2.1
NLOC Loopback.
When NLOC loopback is performed, the channel bank signal is looped back to
the bank at the HLU-D41 and the AIS signal is transmitted toward the CPE. This channel bank
signal is only looped back for the configured bandwidth (time slots). Time slots not configured are
unaffected. The AIS signal is transmitted from the remote unit to the CPE for all 24 time slots.
24.2.2
NREM Loopback.
NREM loopback operates similarly to NLOC loopback except that in NREM
loopback the channel bank signal is looped back to the bank at the remote unit and not at the line
unit. The NI signal is only looped back for the configured bandwidth (time slots). Time slots not
configured are unaffected.
During NREM, the signal transmitted to the CPE from the remote unit depends on the NAIS option
setting. If the NAIS option is enabled, the AIS signal is transmitted from the remote toward the CPE
for all 24 time slots (full T1 bandwidth). If the NAIS option is disabled, the LOS signal is
transmitted from the remote unit toward the CPE for all 24 time slots (full T1 bandwidth).
24.2.3
CLOC Loopback.
When a CLOC loopback is performed, the CI signal that is sent to the HRU-512
is looped back to the CPE at the remote unit (HRU-512). The CI signal is looped back in all 24 time
slots (full T1 signal). At the HLU-D41, the first provisioned (occupied) slot transmits the Abnormal
Station Code ASB (00011110) toward the bank. The second slot transmits 7F and the rest of the
provisioned slots transmit FF toward the bank. Time slots not configured by the HLU-D41 are
unaffected.
24.2.4
CREM Loopback.
A CREM loopback operates similarly to a CLOC loopback except that in a
CREM loopback, the CI signal is looped back to the CPE at the HLU-D41. For the HiGain FT1
system, the CI signal is looped back only on 12 of the 24 time slots (768K maximum bandwidth
capability). The other 12 time slots contain the IDLE code configured via the HLU-D41 IDLE code
option setting (7F or FF). At the HLU-D41, the AIS signal is transmitted toward the channel bank,
but only for the bandwidth (time slots) configured by the HLU-D41 option setting. Time slots not
configured by the HLU-D41 are unaffected.
24.3
Loopback Types (doubler applications).
The doubler loopbacks towards the network (NDU1
and NDU2) operate similarly to NREM except that the loopback location is at the doubler. The
doubler loopbacks towards the customer (CDU1 and CDU2) operate similarly to CREM except that
the loopback location is at the doubler.
24.4
Initiating
Manual
Loopbacks.
A manual loopback session permits you to choose one of the
available HiGain system loopbacks. The Mode Setup button permits you to advance to the next
available loopback and the Choice Setup button permits you to select the listed loopback.
Only one loopback can exist at any given time. If neither push-button is pressed for
a period of 30 seconds and no loopback is in effect, the manual loopback session
terminates and the normal margin displays reappear. If a loopback is in effect, the
30-second time-out is delayed. The active loopback and the manual loopback
session continue until the loopback times out in accordance with the user selected
LBTO setting.
To initiate a manual loopback:
1
Press both the Mode Setup button and the Choice Setup button simultaneously for at least three
seconds.
The following message blinks in one-second intervals:
MAN LPBK
Followed by:
NLO?
