PairGain HIGAIN HLU-231 Manual page 48
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Section 150-231-172
this FAR-END ACTIVATE code. A3LB differs from A4LB in that A3LB supports the additional (1
in 6) Smart-Jack loopback command.
3.7
Two additional loopback points are added for each HDU-451 doubler that is used as shown in Figure
15. NDU1 and NDU2 are executed towards the network. CDU1 and CDU2 are towards the
customer. All four loopbacks can be initiated by the 16 bit in-band commands in SPLB states A1LB,
A2LB & A3LB as described in Tables 15 through 17. NDU1 and NDU2, along with the rest of the
loopbacks towards the network, can be issued from the Loopback Menu shown in Figure 23. See
Section C paragraph 3.10 below for Front Panel-initiated loopbacks. The simplest HiGain system
includes two loopback locations: The HLU-231 List 7B and the HRU-412. The most complex
HiGain system application includes the HLU-231 List 7B, HRU-412 & two in-line HDU-451
Doublers. Refer to the PairGain HiGain Intelligent Repeater Application Note # 910, Part # 325-
910-100, for more SPLB details.
3.8
When T1 loopback tests are performed on the HiGain system with metallic loopback connections at
either end, the DS1 code that exists at the metallic loopback interface may be different from the DS1
code being received at the opposite end when the DS1 user code is set to AUTO. This is caused by
the fact that in the AUTO DS1 code mode, the HLU-231 List 7B & HRU-412 set their own code
independent of each other. Each end sets its transmit code to match its receive code. Thus if one
end is receiving AMI and the other B8ZS, their codes are different. For example, if the HRU-412
has a metallic loopback and the HLU-231 List 7B receive pattern code is first changed from AMI to
B8ZS, and second, the all "0" pattern is sent into the HLU-231 List 7B, the HLU-231 List 7B
changes to its B8ZS mode while the HRU-412 remains in its AMI mode, and thus loops-back the all
"0" pattern. This causes the HRU-412 to indicate a LOS condition, which then causes the HLU-231
List 7B to output the AIS pattern.
3.9
The HiGain system may take longer than normal to respond to in-band loopback commands when its
framing mode is set to UNFR and the in-band commands are sent in either an SF or ESF mode. The
frame bits override the command bits and cause errors in the command sequence. These errors cause
the HiGain system to reject some sequences. This can extend the detection interval.
3.10
Depressing both the MODE and SEL push-buttons on the front panel for at least three seconds
initiates a MANUAL loopback session. This session allows the user to SEL one of eight HiGain
system loopbacks. The message, "MAN LPBK", appears on the front panel display followed by the
message "NLO?". If the SEL push-button is now pressed, an "NLOC" loopback is executed and the
message changes from "NLO?" to "NLOC". If the MODE button is pressed instead of the SEL
push-button, "NLO?" is replaced by "ND1?". This now allows an 'NDU1' loopback to be executed
(if it is a Doubler application) with the SEL push-button. If this same routine is followed, all eight
loopbacks (NLOC, NDU1, NDU2, NREM, CLOC, CDU2, CDU1 & CREM) are presented and can
be initiated in the sequence listed. Pressing the MODE push-button two more times yields the CRE
and CLO loopback options in the sequence listed. This interactive push-button procedure permits
any of the four HiGain loopbacks to be executed/activated.
The next loopback option can be presented by pressing the MODE push-button however, the
previously executed loopback will remain active until the SEL push-button is pressed and a different
loopback is activated. If neither 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 any
loopback is in effect, the 30-second time-out is inhibited. The active loopback and the manual
loopback session continue until the loopback times out in accordance with the user selected LBTO
setting. Only one loopback can exist at any given time. Pressing both buttons again for three
Page 46
January 31, 1997
PairGain Engineering - Plant Series
Revision 02
HiGain Line Unit HLU-231
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