VoIP Voice and Fax Signal Processing

17.3 CALL PROGRESS TONES FOR MULTIPLE COUNTRIES

This section is presented with the electrical characteristics of various tones used in PSTN or VoIP services. In telephone service, the outcome of communication would be either visual or acoustic. Most actions in the telephone are audible acoustic tones and speech. The tones are known by name call progress tones (CPTs) as they represent the progress of the call. The tones in different countries and regions will vary. Some basic tones such as dial tone, busy tone, ring back tone, congestion tone, and call waiting tone are given in E.180 [ITU-T-E.180/Q.35 (1998)] for most countries. Many extended tones are available in local PSTN standards, for example, [URL (NTT-E)].

The most popular visual information on a phone are message waiting indicators, caller ID, call wait ID display, any light blinking associated with off-hook, ring, or call progress indication. Some phones with sufficient size display may also display dialed digits, date, time, and new call indication through selected symbols in the same screen of caller ID display.

17.3.1 Basic Call Progress Tones

Most tones mentioned in this chapter are applicable to both the PSTN and VoIP. In the case of the PSTN, a central office will deliver these tones. In VoIP, the VoIP adapter in association with call control signaling delivers the tones. These tones are given in a generic way. Specific details have to be noted from country-specific PSTN standards and E.180. The basic tone parameters ...