Cisco GS7000 Installation And Configuration Manual page 101

Status Monitor/Local Control Module
Note: The local control module can be upgraded to a status monitor through the
addition of a transponder core module. The transponder core module plugs
directly onto the local control module's PWB. The mechanical housing for the
status monitor and the local control module are the same. The Heart Beat, Receive,
and Error indicator LEDs are only present if the transponder module is installed.
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