VoIP Voice and Fax Signal Processing

8.2 FSK CALLER ID DATA TRANSPORT PROTOCOL

The basic data transport protocol for caller ID is divided into four layers, namely,

1. Physical layer
2. Data link layer
3. Presentation layer
4. Application layer

The first three layers provide the actual data transport, and the application layer is used for caller ID-specific data and signaling for alerting the TE.

8.2.1 Physical Layer

The physical layer provides the interface between the caller ID service and the analog line. The physical layer provides two main functions of data transmission of service-specific information and signaling mainly for alerting the TE.

The data transmission is performed using continuous-phase FSK modulation. Data is always sent as serial binary bits in simplex mode. Data transmission is continuous, and no carrier dropouts are allowed. The start of data transmission must not corrupt the first data bit. The data transmission is stopped immediately after the last bit of the data-link message. The FSK data is sent asynchronously at a signal level of −13.5 dBm in both ETSI and Telcordia recommendations as listed in Table 8.1. This power level is applicable at the central office. The FSK signal level may differ for each country, because of country-specific deviations of overall loudness rating (OLR) as well as because of send and receive gain/loss planning. To get a first-level understanding on ETSI and Telcordia basic specifications, a summary is given in Table 8.1. It is suggested to refer to the ETSI [ETSI ETS 300 659-1 ...