The principle of operation of AON. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Telephony

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Caller ID in its work uses the following parameters of PBX signals:

• Telephone line voltage (on-hook) - 60 V
• Inductor call signal amplitude with incoming connection 50-100 V; pulse shape - bell-shaped, frequency - 25 Hz
• Voltage in the telephone network when off-hook 5-8 V
• Dialing speed 9-11 pulses/s, dialing pulse rate 1.3-1.9
• Signal "Dial Answer" - a continuous tone signal with a frequency of 425 Hz
• Busy signal - 425 Hz (duration and pause - 0.35 s)
• Ringback control signal - 450 Hz (pulse duration 1 s, pauses - 4 s)
• "Hang up" signal - holding the handset on the device lever for more than 1.2 s

Caller ID information request signal parameters:

• Time from connecting caller ID to the line to issuing a request (t pause) - 250-275 ms
• Request signal duration (t request) - 100 ms
• The level of the request signal (U zapr) - 4.3db (the effective voltage of the request signal).
• Request signal frequency (f lock) - 495-505 Hz

Number identification principle:

The ATS-1 subscriber picks up the handset and calls the ATS-2 subscriber. At the same time, the ATS-2 subscriber receives an inductor call via the telephone network (a call from the ATS). Caller ID phone of the subscriber-2 is connected to the telephone line, lowering the voltage to the level of 22-24 V - blocking the conversational path. Then, after 250-275 ms (the time for the end of transients when switching the telephone line), the ANI of subscriber-2 gives out to the PBX-1 the signal "ANI Request" with a frequency of 495-505 Hz with a level of 4.3 dB and a duration of 100 ms. On PBX-1 this signal is decoded and "Answer" is issued - the phone number of the calling subscriber of PBX-1 using the multi-frequency method "intervalless packet" in the received code "2 out of 6". Caller ID at subscriber-2 receives a packet of frequency information in the order in which it arrives, followed by decoding the combination.

Frequency information - a sequence of two-frequency messages from a number of frequencies:

Combinations of two of the six above frequencies denote the following:

"Start" - means the beginning and end of a packet of two-frequency messages (a multi-frequency sequence has several times a repeating packet of information, the beginning and end of which is indicated by this combination).

"Repeat" - means that the next digit repeats the previous one (in the absence of this combination, the decoding of two consecutive identical digits would be extremely difficult).

The information packet contains 10 two-frequency packets with a duration of 38-42 ms with the following transmission sequence:

1. "Start"
2. Category digit
3. Number units digit
4. Number tens digit
5. Number hundreds digit
6. Number thousands digit
7. Third digit of the station index
8. Second digit of the station index
9. The first digit of the station index
10. "Start"

The information is processed by the microprocessor and displayed on the indicator. At the same time, in the subscriber's telephone-2 (AON) signals are generated that imitate the CPV signal (Call Sending Control - long intermittent beeps). Further, if necessary, subscriber-2 can carry on a conversation - the Number Identification algorithm has ended.

Physical basis of multifrequency signal processing

The figure shows a fragment of a two-frequency message.

A similar signal is fed to the input of the comparator (electronic comparison circuit), and the comparison potential (level) is applied to the other input. Anything above the compare level of the comparator is evaluated as a high potential at the output, and anything below is "0".

The digitized signal is input to the I/O port. The central processing unit (CPU), under the control of a program stored in ROM (read only memory), polls the state of the I / O port (comparator state) with a certain frequency, placing the results in the temporary memory of the device - RAM. Then the results - a sequence of "0" and "1", recorded in RAM in a certain sample (the duration of the sample depends on the size of the allocated memory so that the results do not overflow the RAM), using special programs for digital analysis of a harmonic signal, are analyzed by the CPU and identified with a specific signal : numbers 0,1-9, "start", "repeat". Working in real time, the CPU, during the passage of one two-frequency message (40 milliseconds), manages to analyze it up to 5 times, thereby making it possible to compare the results, which has a positive effect on the efficiency of number detection. During the response time, the CPU performs 50-150 such samples to obtain an unambiguous decision: what is the category and number of the caller.

Publication: cxem.net

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