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Testing
L
O
OOPBACK
PERATION
HDSL4 has a family of loopback options for analyzing circuit functionality. The loopback signal is transmitted
and returned to the sending device for comparison. This allows you to verify the integrity of the HDSL4 channels
to the H4TU-C, the H4TU-C DSX-1 interface, and the DS1 channels to the customer.
Loopback options include:
•
Generic Loopback (GNLB) options, including the SmartJack (SMJK) option (see
•
A3LB Addressable Repeater Loopback command (see
•
A5LB Addressable Repeater Loopback command (see
Loopback commands can be initiated by:
•
Selecting the loopback type using the MODE and SEL pushbuttons on the H4TU-C front panel or the manual
loopback (LBK) pushbutton on the H4TU-R front panel
•
Selecting the loopback type from the Monitor menu when connected to the craft port of the H4TU-C or
H4TU-R
•
Entering the loopback code (exceptions are COLB and RULB) into the test equipment connected to the
H4TU-C or H4TU-R
Activate loopback using
DSX-1
one of the following:
• MODE/SEL pushbuttons
NLOC
• Maintenance Terminal
• Test Set
Network
ADC HDSL4 supports multiple loopbacks, but a single loopback is the preferred method. HDSL4
automatically rejects activation of closed loop looopbacks. For example, an NREM and CREM
cannot be activated at the same time.
46
Span 1
CREM
NDU1
CDU1
H4TU-C
H4D1
*
When enabled, TLOS is an automatic loopback
that occurs with an LOS at the remote DS1 input.
Figure 28. Loopback Summary
September 12, 2003
Table 17 on page
52)
Table 18 on page
53)
Span 3
Span 2
NREM
NDU2
CDU2
SMJK
TLOS*
H4D2
LTPH-UM-1031-03, Issue 3
Table 16 on page
51)
Activate loopback using
one of the following:
• LBK pushbutton
CLOC
• Maintenance Terminal
• Test Set
H4TU-R
Customer
Premises
H4TU-C-319 List 1
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