AT&T MERLIN LEGEND Installation & Maintenance Manual page 82

System Description
The unprotected mode must be used for an E&M type 1
standard interface (see below) to meet the specified voltage-
drop criteria. This mode is used when there is a network
interface.
CAUTION:
The protected mode must be used whenever the E&M leads
extend out-of-building and are not connected to the network
interface.
Signaling Types
Three different signaling types combine with the signaling
modes. Together these create the proper signaling format for
each system.
Type 1 standard. This is the factory-set type, which is used
to connect two systems through two intermediate COs. The
switches must be set for E&M mode.
Type 1 compatible. This type is used to connect directly
without intermediate COs. One system is set to type 1
standard, the other to type 1 compatible. The switches must
be set for E&M mode.
Type 5 simplex. This type is used to connect similar systems
or systems with compatible signaling that are Iocated in the
same building or on the same business campus.
The choice of a tie-trunk signaling format depends on the
particular application and the two systems being connected,
including whether or not the tie-trunk signals pass through CO
lines or over customer-owned cable. Table 1-10 shows how to
determine tie-trunk compatibility between the MERLIN LEGEND
Communications System and other systems.
Signal Processing 1-51