DE4016629A1 - Service telephone unit with dual-tone multi-frequency decoder - protects service conversations by provision of engaged tone from internal generator and switch operated by microcontroller - Google Patents

Abstract

The decoder (2) is linked by a data bus (2a) and an address bus (2b) to a microcontroller (6) which compares received and decoded calling signals with a stored call number. In the absence of correspondence, two switches (8,11) remain open so that subscribers cannot speak or listen to the service channel. If a subscriber lifts his or her handset during a service conversation, an engaged tone is heard from a controllable reversing switch (10) connecting a tone generator (5) to the line. USE/ADVANTAGE - For transmission system monitoring and maintenance. Unwanted interference with selective calls is prevented.

Description

The invention relates to a service telephone unit a microcontroller, a DTMF decoder, an audible tone generator, as well as a handset with an earpiece and a microphone.

Such units are part of service lines facilities which in turn are used for monitoring and Maintenance of transmission systems are required. In an article by Seidel (Seidel, H .: services FO transmission lines. telcom report 10 (1987), Issue 1, pages 38 to 43) is a service facility device with associated service telephone unit described.

Service facilities are at intermediate regenerator places or end points of transmission lines in Über guard stations are housed and over a Du plex channel, the service channel, interconnected the. The service channel is a 64 kbit / s channel of the (digital) main signal and is (in both directions) in front of a service facility from the main signal decoupled ge by the service facility loops and then coupled back into the main signal pelt.

From the monitoring stations or service facility the service personnel can perform any other service transmission system or a subscriber the public telephone network through a selective call call. Group calls (call to all stations) are also and group calls (call to a group of stations) possible Lich.  

A disadvantage of the known service telephone unit is that even when a selective call is not made Participants (here the service personnel) can "hook up" nen, d. H. to be active or passive at any time can participate in the conversation.

The invention has for its object one called service telephone unit for a service line to specify facility that an unwanted intrusion prevented with selective calls.

This task is carried out by the solved 1 specified characteristics.

Advantageous configurations are in the subclaims specified.

Based on the figure, an embodiment of the inven be described in more detail.

The figure shows a basic circuit diagram of a remote service Talking unit with features according to the invention.

Via an input line 1 a of the service telephone unit according to the figure, the signal of the service channel is supplied. Via an output line 4 a signals emitted by the unit are fed to the service channel. The signals are transmitted analogously on the input line 1 a and the output line 4 a.

To illustrate the operation of the circuit sol A distinction is first made between two cases: In the first case, the service telephone shown is the one called unit-using participants - hereinafter Called participant A - otherwise he is himself Caller.  

In the first case, there is a sequence of dialing characters on line 1 a (for more details, see below) that result in a telephone number, each dialing character being coded using the multi-frequency method - also known as the DTMF method (Dual Tone Multi Frequency). According to this method, each dialing character is encoded by two frequencies in the voice band. Compare the CCITT recommendation Q.23.

Each of the incoming characters is fed via a first signal adder 1 to a DTMF decoder 2 , which is connected to a micro controller 6 via a data bus 2 a and an address bus 2 b. The callsigns are stored in PCM coding in memory units of the microcontroller 6 via the data bus, the addresses of which are also supplied by the DTMF decoder 2 .

Now the microcontroller 6 compares the sequence of the read callsign with the phone number stored in one of its memories. Again there are two options: Either the received callsign matches the sequence of the saved callsigns or this match does not exist.

If they do not match, a switch 8 and a switch 11 remain open. The switch 8 is controlled by the microcon troller 6 via a control line 6 c and the switch 11 via a control line 6 b. In its open position, the switch 8 interrupts the connection which leads from the input line 1 a via a second signal adder 9 and line 9 a to the (not shown) earphone of the handset, also not shown. As long as switch 8 is open, subscriber A cannot overhear conversations made via the service channel (passive participation). The switch 11 interrupts the compound b by the microphone of the handset over a portion of the conduit 1, c a line 4, a third signal adder 4 and the output line 4a leading to the facilities that a signal on the output line 4 on the service channel transfer. As long as switch 11 is open, no signal from subscriber A can be given to the service channel; his active participation in a conversation with a previous selective call to another subscriber is also prevented.

Simultaneously with the actuation of the switches 8 and 11, a change-over switch 10 c of the Mi crocontroller 6 via a control line 6 such gesteu ert in the present case, that it the output of a Hörtongenerators 5 via the signal adder 3 and the conduit 9 a to the input of A participant's earpiece connects. If the participant A takes off his handset in the present case, the audio tone generator 5 is switched on and off via a line 6 e from the microcon troller 6 in the rhythm of the busy tone. If the received number and the stored number match, the following operations are carried out with control signals from the microcontroller 6 :

• a) an alarm clock 7 is put into operation via a line 6 d,
• b) via the lines 6 b and 6 c, the switches 11 and 8 are closed,
• c) via the line 6 a, the switch 10 is brought into a position in which it connects the output of the Hörtonge generator 5 to a line 4 b, which leads to an input of the signal adder 4 ,
• d) via the line 6 e, the audio tone generator 5 is switched on and off in the rhythm of the dial tone.

Because of measures b), subscriber A can actively and passively participate in the desired conversation. Because of the measures c) and d) the calling subscriber receives the free sign of the tone generator 5 and thus knows that his choice was successful.

If the participant A responds to the alarm clock 7 , he lifts his handset and thus brings a fork switch 12 into its second position. Via a line 12 a, the microcontroller 6 is informed of the changed switching position of the hook switch 12 and at the same time a current source 13 for the microphone of the subscriber A is switched on. Induced by the signal on line 12 a, the microcontroller 6 turns off the Hörtonge generator 5 and the alarm clock 7 . The dialogue between the two participants can now begin.

If subscriber A is the calling subscriber, he will lift his handset and thus change the switching state of the hook switch 12 . The changed state is registered by the microcontroller 6 via the line 12 a. The microcontroller 6 now queries a specific one of its in internal memory, in which the DTMF character A or B is stored in binary form. The characters A and B are given at the beginning or at the end of a conversation on the service channel, pass through the input line 1 a and the signal adder 1 into the DTMF decoder 2 , are recoded by the latter in binary characters and together with special ones Transfer addresses via the bus lines 2 a and 2 b to the Microcon troller 6 .

The symbol A means that the service channel is busy, the symbol B that it is free. Is in the above-mentioned memory, the character A is stored, the Microcon the means controls troller 6 5 and 10 in such a way that the subscriber A a a busy signal is obtained via the line. 9 If, however, the character B is stored, the subscriber A receives the dial tone. He now operates the keyboard on his handset, which generates the corresponding DTMF characters. This pass via the line 1 b and the Si gnaladdierer 1 to the DTMF decoder 2, the corresponding PCM mark passes it to the microcontroller. 6

This now checks whether the character string entered by the participant is permissible. If the character string is not allowed, subscriber A receives the busy tone and if the character string is allowed, this is transmitted with the preceding DTMF character A to a DTMF coder 3 and given via signal adder 4 to output line 4 a. The DTMF character A, which is stored in the microcontroller of all other subscribers, has the consequence for these subscribers that they receive a set tone in the event of a dial attempt.

After sending the number, switches 8 and 11 are closed, the conversation can now begin. At the end of the conversation, subscriber A, for example, hangs up his handset first. The microcontroller then sends out the DTMF character B, which is stored in the same memory in which the character A was previously stored. The letter A is overwritten by the letter B. This process is carried out for all subscribers who are connected to the service channel.

By using the DTMF special characters A and B wer collisions when accessing the service channel different. The service telephone unit according to the invention can without further introduction of additional features to, such as the collective call, the group call and Priority when accessing the service channel. The latter  For example, the feature allows the interruption an existing conversation by a third party to a Make an emergency call.

Claims (4)

1. Service telephone unit with a microcontroller ( 6 ), a DTMF decoder ( 2 ), an audio tone generator ( 5 ), and a handset with an earpiece and a microphone, characterized by the following features. 1.1. the DTMF decoder ( 2 ) is connected via a data bus ( 2 a) and an address bus ( 2 b) to the microcontroller ( 6 ), which receives the received number via an input line ( 1 a) and then decodes it with a stored number compares 1.2. if the two numbers do not match

• a) the microcontroller ( 6 ) holds a first controllable switch ( 8 ) in a position in which the connection between the input line ( 1 a) and the earpiece is interrupted and holds a second controllable switch ( 11 ) in a position in which also the connection between an output line ( 4 a) and the microphone is broken,
• b) the microcontroller ( 6 ) controls a changeover switch ( 10 ) such that the output of the audio tone generator ( 5 ) is connected to the input of the earpiece,
• c) the microcontroller ( 6 ) switches the audio tone generator on and off in the rhythm of the busy signal.

2. Service telephone unit according to claim 1, characterized in that a DTMF coder ( 3 ) is provided which is connected to the micro controller ( 6 ) via a data bus ( 2 a) and an address bus ( 2 b) that at The start of the conversation from the microcontroller ( 3 ) transmits a first DTMF special character in binary form to the DTMF code ( 3 ), is sent to all participants in coded form and the microcontroller ( 3 ) of all participants is stored in a special memory so that when the call ends in the in the same way, a second DTMF special character is transmitted with which the first special character is overwritten and that a subscriber can only set up a call if the second special character is stored in the special memory of his microcontroller ( 3 ).