Mitel 300 Installation And Maintenance Manual page 40

There are six indicators (LEDs) on the MDF cover.
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Heartbeat – flashes to indicate normal processor activity
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ADSL - a solid light indicates ADSL line synchronisation
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LAN 1 - a solid light indicates an Ethernet connection
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LAN 2 - a solid light indicates an Ethernet connection
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LAN 3 - a solid light indicates an Ethernet connection
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LAN 4 - a solid light indicates an Ethernet connection
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There is an additional indicator inside on the MDF. This is the WAN indicator - a solid
light indicates an Ethernet connection
Mitel 3000 Australia Installation and Maintenance Manual
39