AT&T 518-600-016 manual Theory of Operation

●Unprotected mode: Must be used for the E&M

Type 1 Standard interface in order to meet voltage drop criteria for the interface. This mode is used when there is a network interface.

●Protected mode: Resistance is added in tie M lead to provide additional protection from foreign voltages and transients. This mode is used on local tie lines, such as between systems in different buildings.

●Simplex mode: The signaling leads are superimposed onto the analog transmission leads to provide a two- pair interface. Resistance is included in the signaling leads for protection from foreign voltages and transients. This mode is used primarily with E&M Type 5 signaling on local tie lines.

Signaling Type Signaling type designates the logical signaling used. There are the following three options:

●Type 1 Standard (default): The M leads are used for signaling from PBX to line. Off-hook is -48 VDC and on-hook is local ground. Signaling in the other direction uses local ground for off-hook and open for on-hook.

●Type 1 Compatible: This interface is back-to-back compatible with Type 1 Standard. It allows direct connection between systems where no intermediate signaling equipment is used.

●Type 5: A symmetrical 2-wire arrangement that signals in both directions by means of open for on-hook and ground for off-hook. The primary application of Type- 5 interface is local tie lincs.

1-48 Theory of Operation