Section 150-611-103
Revision 01
Page 12
9.04
The A1LB loopback selection (Table 4)
complies with that proposed for VHDSL
systems in the T1E1.4/92 recommendation with the
following additions:
1) Query loopback
2) IOR powerdown
3) Three loopback time-out choices
4) Initiation from either end
5) Repeating bit error signatures
6) Alternate Query loopback
These additions make A1LB identical to A2LB
described below. It is given a separate identity to
allow future T1E1 enhancements to be added
without affecting A2LB.
9.05
A2LB through A5LB are four special
addressable repeater loopback functions
which are supported by the List 6 version of
HiGain-2. These loopbacks provide HiGain-2 with
sophisticated maintenance and trouble shooting
tools. Tables 5 thru 8 list the details of these
Special Loopback (SPLB) functions. A2LB & A5LB
are patterned after the Teltrend addressable T1
repeater loopbacks. A3LB & A4LB are patterned
after the Wescom addressable T1 repeater
loopbacks. All four SPLBs have been enhanced to
handle the specific requirements of the following
HiGain-2 customers:
•
A2LB (Teltrend) = Southwestern Bell
•
A3LB (Wescom)=New England Tel.
•
A4LB (Wescom Mod 1) =New York Tel.
•
A5LB (Teltrend Mod 1) =Southern New
England Tel. (SNET)
9.06
A5LB differs from A2LB in that A5LB does
not block the arming ( 3 in 5) code from
exiting the HLU into the network. A2LB can be
configured to either block this arming code after 2
seconds, and replace it with the AIS code, or to
unblock it by executing the FAR-END ACTIVATE
code. Since A5LB never blocks the arming code
from exiting the HLU, it does not need this FAR-
END ACTIVATE code. A3LB differs from A4LB in
that A3LB supports the additional 1 in 6 smart jack
loopback command. Refer to the PairGain HiGain-2
Intelligent Repeater Application Note # 910 Part #
325-910-100 for more SPLB details.
9.07
When T1 loopback tests are performed on
the HiGain-2 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 &
HRU 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 has a metallic loopback and the HLU’s receive
pattern’s code is changed from AMI to B8ZS and then
the all 0 pattern is sent into the HLU, the HLU changes
to its B8ZS mode while the HRU remains in its AMI
mode and thus loops all 0’s. This causes the HRU to
indicate a LOS condition which then causes the HLU
to output the AIS pattern
9.08
HiGain-2 may take longer than normal to
respond to inband loopback commands
when its framing mode is set to UNFR and the
inband 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 HiGain-2 to reject some sequences.
This can extend the detection interval.
C. INSTALLATION AND TEST
10. INSTALLATION
10.01
Upon receipt of the equipment, visually
inspect it for signs of damage. If the
equipment has been damaged in transit,
immediately report the extent of damage to the
transportation company and to PairGain.
10.02
The HLU-611 is designed to mount in a 220-
type ORB shelf or equivalent SXSS, Kentrox
T-Term and Wescom 342-30 shelves. The HLU-611
slot pin-outs are shown in Figure 4.
CAUTION
The ALM option must be disabled (DIS)
when using the Kentrox 220 T-Term shelf.
This is required to resolve a conflict
between the HLU alarm relay output and
the Kentrox external equalizer output. Both
use the same pins, 20 and 21.
