Mitel 5540 - LDN Keys (Listed Directory Number); PABX (Private Automatic Branch Exchange); Recall; Software

Mitel 5540 IP Console - User Guide
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LDN Keys (Listed Directory Number)
Call-handling keys which allow you to select the sequence in which you answer calls from
outside the PABX.
PABX (Private Automatic Branch Exchange)
Telephone switching system for private use by a company.
Recall
A call which returns to the console after being transferred to a busy or unanswered extension.
Software
The routines, programs, and instructions required to run the system.
Trunk
A trunk (outside line) is the external communications link between two switching systems. This
link can be between one or more telephone systems (PABXs) or the PABX and Central Office
equipment.