Exp dtmf n advantages of dtmf over pulse dail mech
Draw n explain caller id
What do u mean by cross talk n exp diff types of cross talk
What do u mean by side tone and its importance
Exp pagging system in detail
Draw n exp functional block diagram of telephone set
Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center. The version of DTMF that is used in push-button telephones for tone dialing is known as Touch-Tone, was first used by AT&T in commerce as a registered trademark, and is standardized by ITU-T Recommendation Q.23. It is also known in the UK as MF4. Other multi-frequency systems are used for internal signaling within the telephone network. The Touch-Tone system, using the telephone keypad, gradually replaced the use of rotary dial starting in 1963, and since then DTMF or Touch-Tone became the industry standard for both cell phones and landline service.
The DTMF keypad is laid out in a 4×4 matrix, with each row representing a low frequency, and each column representing a high frequency. Pressing a single key (such as '1' ) will send a sinusoidal tone for each of the two frequencies (697 and 1209 hertz (Hz)). The original keypads had levers inside, so each button activated two contacts. The multiple tones are the reason for calling the system multifrequency. These tones are then decoded by the switching center to determine which key was pressed. |DTMF keypad frequencies (with sound clips) | | |1209 Hz |1336 Hz |1477 Hz |1633 Hz | |697 Hz |1 |2 |3 |A | |770 Hz |4 |5 |6 |B | |852 Hz |7 |8 |9 |C | |941 Hz |* |0...
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