AT&T MERLIN LEGEND Installation & Maintenance Manual page 81

System Description
This process also involves time slot interchanging so that an
available slot in the TDM cycle can be filled with a transmit or
receive slot. The DSE allows up to 16 time slots to be
conference and sent out to a single station port.
Tie-Trunk Signaling
Tie trunks transmit via three different signaling formats, each
made up of a specific mode and a specific type.
The DIP switches on the 400EM module select the signaling
modes needed for tie-trunk transmission (see Figure 72); the
signaling type is selected during system programming.
Signaling Modes
There are two signaling modes:
Simplex mode. Two signaling leads superimposed onto the
analog transmission leads provide a 2-pair wire interface for
connecting two local systems at minimal cost.
E&M mode. This is a standard interface. The E&M signaling
leads are isolated from the transmission leads, requiring a
3-pair wire interface.
In the simplex mode, protective resistance is always included in
the circuit. The E&M mode can be either protected or
unprotected from high-voltage transients or fluctuations. In the
protected mode, a resistance is added to the leads to reduce
current peaks. The protected mode is used when there is no
network interface to protect the circuit from outside interference.
1-50 Signal Processing