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152-388-100-02, Issue 2 Testing
H2TU-C-388 List 1 June 6, 2000 41
Special Loopback Commands
In addition to the GNLB loopback command mode, a HiGain system can be configured for one of five special
loopback command modes. These are selected from the maintenance terminal System Settings screen (see Table 5
on page 17) or by using the MODE and SEL buttons (see Figure 27 on page 44). Once a loopback mode is
activated, other loopback commands can be sent by a test set connected to the craft port of the H2TU-C or
H2TU-R (see Table 16 on page 45 and Table 17 on page 47 for list of SPLB commands).
A1LB through A5LB are five special, addressable, repeater loopback modes which are supported by the
H2TU-C-388 List 1. These loopback modes provide the HiGain system with sophisticated maintenance and
troubleshooting tools. A1LB, A2LB, and A5LB are patterned after the Teltrend addressable DS1 repeater
loopbacks. A3LB and A4LB are patterned after the Wescom addressable DS1 repeater loopbacks. All five SPLBs
have been enhanced to handle the specific requirements of the following HiGain customers:
• A1LB (Teltrend) = Southwestern Bell
• A2LB (Teltrend) = Southwestern Bell
• A3LB (Wescom) = New England Telephone
• A4LB (Wescom Mod 1) = New York Telephone
• A5LB (Teltrend Mod 1) = Southern New England Telephone (SNET), Southwestern Bell, Pacific Bell
The A1LB loopback selection complies with that proposed for HDSL2 systems in the T1E1.4/92 recommendation
with the following additions:
• Query loopback
• IOR (Intelligent Office Repeater) powerdown
• Four loopback time-out choices
• Initiation from either end
• Repeating bit error signatures
• Alternate query loopback
These additions make A1LB identical to A2LB. A1LB is given a separate identity to allow future DS1/E1
enhancements to be added without affecting A2LB.
A5LB differs from A2LB in that A5LB does not block the arming code from exiting the H2TU-C-388 into the
network. A1LB and A2LB can be configured to do one of the following:
• Block the arming code (after 2 seconds) from exiting the H2TU-C into the network, and replace it with the
AIS code.
• Unblock the AIS code by executing the Far-End Activate code. (Since A5LB never blocks the arming code
from exiting the H2TU-C, the Far-End Activate code is not available in A5LB.)
A3LB differs from A4LB in that A3LB supports the additional (1-in-6) SMJK loopback command.