Inpagingservices, the messages supported by a service or a pager are called call classes. A distinction is made between four different call classes, which vary from service to service. Not every call class is supported by every service.
Call class 0 is the tone call, also referred to as "tone only". This call class is set up for single-valued messages, whereby the presentation can be a tone signal, a luminous display or a vibration.
Call class 1 (RLK 1) is the call class for numeric presentations. In this call class, multi-digit sequences of up to 15 digits can be presented, for example telephone numbers. In addition to the numeric representation, two tone-only signals can be booked
Call class 2 designates the class for text and alphanumeric. With this call class, alphanumeric texts can be transmitted, which are shown on the display of the pager
Call class 3 is the class for the transmission of transparent data. In this call class the subscriber can encode his message.