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Maintenance Description
9-36 Issue 3 June 2001
Loopbacks 9
The DDM-2000 OC-3 Multiplexer allows technicians to set up loopbacks on all
low- and high-speed interfaces. Low-speed DS1, DS3, and EC-1 electronic
loopbacks, directed toward the high-speed OC-3, can be individually controlled
from the CIT. Facility loopbacks can also be set up towards the DSX on all low-
speed DS1, DS3, and EC-1 interfaces. DS1 facility loopbacks can only be set up
in groups of four on the BBF1(B) and BBF3 circuit packs. Individual DS1 facility
loopbacks are available with the BBF3B and the BBG20 (TMUX) circuit packs .
Active electronic loopbacks are noted by the user panel's abnormal (ABN)
indicator and in the Alarm and Status report. Refer to the opr-lpbk and rls-
lpbk commands in Section 11, "Commands and Reports."
Front access to the OLIU optical connectors allows an easy manual OC-3 or OC-
1 optical loopback. This loopback is set up by connecting a fiber jumper from the
OLIU output to its input. An optical attenuator is required for this loopback if the
22G-U, 24G, 26G2-U, 27G2-U and 29G OLIU is used. Other types of OLIUs do
not require attenuators for this loopback.
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