Line and Register Signaling

CAS is traditionally divided into line signaling and register signaling. There is no need for this division in CCS.

Line signals are simple information in contrast to register signals. Line signals are needed during the whole call while register signals are used only during the call set up.

By dividing the signaling equipment into register and line signaling equipment, and using the more complex register equipment only while the address information is transmitted, one register equipment may be used to serve many lines.

Notice the difference between this division based on what information the signals transfer, and divisions based on the different principles of signaling (for example, CAS, CCS see above) or techniques used to transfer the signals (for example, impulsing, tone code).

Line signaling

Seizure, answer and clearing are examples of line signals.

Examples of techniques used for line signaling are DC signaling (Direct Current) and digital signaling (in time slot 16 on a PCM link).

Register signaling

This is mainly used for conveying the called number.

Examples of techniques used for register signaling are impulsing (decadic pulsing) and tone code (for example, DTMF, MFC).