September 2008
Intermediate to advanced
550 pages
18h 10m
English
Content preview from VoIP Voice and Fax Signal ProcessingBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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8.3 DTMF-BASED CALLER ID
Most caller ID signals use FSK-based implementation. Some countries like Finland, Denmark, Iceland, the Netherlands, India, Belgium, Sweden, Brazil, Taiwan, Saudi Arabia, and Uruguay make use of DTMF-based caller ID. In practice, many DTMF-caller-ID-supported phones are also made to work with FSK-based called ID. The phone displays are capable of supporting the numbers and alphabets. In the case of DTMF caller ID, only a number display is supported.
8.3.1 DMTF Caller ID on PSTN
For the transfer of display information over analog subscriber lines, 16-DTMF digits are used in DTMF-based caller ID. Except for these special display procedures, the normal signaling procedures and physical properties for analog subscriber lines also apply to DTMF caller ID [ETSI ETS 300 659-1 (2001)]). In case of an incoming call for a subscriber, the exchange shall seize the corresponding subscriber line for the terminating call. The line seizure may be indicated to the subscriber line by means of a polarity reversal of two lines of TIP-RING or through ring alert. In line reversal, the return to the idle polarity takes place after the information transfer phase. Two different modes for the data transmission are possible with DTMF—namely data transmission before the first ring and data transmission between the first and the second ring.
Data Transmission Before the First Ringing. In this mode, the data transmission shall occur before the beginning of the first ringing pattern. ...
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