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MERLIN LEGEND Communications System Release 6.1
Installation
555-661-140
Issue 1
August 1998
Installing the Control Unit
Page 2-35
Installing the Modules
Tie Trunks
Tie trunks connect two separate PBX communications systems either
directly or through one or more central offices, as if they were one
system at the same location. In the MERLIN LEGEND Communications
System, the 400EM module is the originating and terminating unit for tie
trunk operation.
Tie Trunk Signaling
The 400EM (tie trunk) module can transmit signals in three different
formats. Each format is made up of a specific signaling mode and a
specific signaling type. The DIP switches on the 400EM module allow
you to select the signaling mode for tie trunk transmission. The signaling
type is selected through system programming.
Signaling Modes
There are two signaling modes:
■ E&M. This is a standard interface. The E&M signaling leads are
separate from the transmission leads, requiring a 3-pair wire
interface.
■ Simplex. In Simplex, the two signaling leads are superimposed
onto the analog transmission leads, providing a 2-pair wire
interface for connecting two local systems at minimal cost.
Protected or Unprotected
Depending on the type of tie trunk installation, protective resistance may
be installed to protect the circuit from outside interference from
high-voltage transients or voltage fluctuations. In Simplex mode, the
circuit always requires protective resistance. The E&M mode can be
either protected or unprotected, depending upon the location of the
distant PBX.
Signaling Types
Three different signaling types combine with the signaling modes.
Together, these create the proper signaling format for each system.
Signaling types in each mode are as follows: