DK143378B - CONNECTING FOR SECURE RECOGNITION OF THE TRANSFER GRANT IN THE RECEIVING STATION IN THE DATA TRANSFER - Google Patents

Description

(19) DENMARK \ | j ^ /

||| (12) FOREIGN SCRIPTURE (11) 143378 B

DIRECTORATE OF THE PATENT AND TRADEMARKET SYSTEM

(21) Application No. 4τ4ΐ / 70 (51) IntCi. * H OA L 27/26 (22) Filing Day 15 · Bep. 1970 H OA Q 1/46 (24) Race day 15. s ep. 1970 (41) Aim. available Mar 17 1971 (44) Presented 10 Aug. 1981 (86) International application no. - (86) International filing day - (85) Continuation day - (62) Master application no. -

(30) Priority Sep 16 1969, 19468, DE

(71) Applicant SIEMENS AKTIENGESELLSCHAFT, Berlin and Munich, 8 Munich 2, DE.

(72) Inventor Eberhard Lukas, DE: Ernst-Alfred Fuchs, DE. j (74) Clerk of International Patent Office.

---------- 11 ........ "1 ··· ....... .....-...... '' (54) Link to secure recognition of the transmission start in the receiving station in the data? * transmission facility.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a coupling for securely recognizing the commencement of a data transmission at a receiving station of a data transmission system, at which data signals are transmitted by multi-frequency signals, the receiving station comprising quality and when received correctly, a first output J signal is output and a wrong output received a second output signal.

In data transmission, it is necessary that the beginning of data transmission j be recognized in the receiving data station and that data delivery devices such as) e.g. printing apparatus, hollow strip apparatus, hole card apparatus, acoustic or optical dispensers, computer monitors, etc. are released for recording data.

The beginning of the transmission is recognized by known means by means of a level monitoring device which responds to the occurrence of the receiving voltage and releases the data delivery device. However, if there is a disturbance on the receiving line, a reaction of the data delivery device is reacted, and faulty data produced by the disturbance is output. This risk is particularly high in data transmission devices operating over a telephone dialing network, in which such data is generated in the transmission interruptions as a result of voter noise in the connection establishment locations. In order to be able to sufficiently distinguish the onset of transmission from a disturbance, expensive level monitoring such devices are necessary.

However, there is a class of data transfer devices, in particular data collection facilities, at which such expense is excessive, these devices having to be simple and inexpensive. At these plants, data is transmitted, e.g. in the form of data blocks, from a large number of terminal stations over the telephone selector network to a data center. The length of the data blocks is e.g. given by the length of an order number and a piece number or by the storage capacity of a hole card. The data center verifies the transmitted data and their accuracy. At the end of the data block, the terminal station is switched from "sending" to "receiving" and invokes a response signal from the data center. The data center transmits to the terminal station only acknowledgment signals to acknowledge receipt of such order data, or it transmits the requested information as a response, which information is transmitted to the terminal station in analog form and is transmitted here over a loudspeaker. In this mode of operation, a secure recognition of the commencement of transmission in the received data station is important, as otherwise faulty data is provided.

A monitoring coupling is already known, in which the receive signal level is exceeded by a threshold value for a specified period (35ms), and in the event of a disturbance an error signal is output (Siemens-Zeitschrift Vol.43, March 1969, no. 3 pages 129-135 , "Modems for the parallel transmission of data on five voice dialing networks"). The receiver coupling includes a level monitoring coupling with a timing link and a quality rating coupling. When the receiving level for a period of 35 ms in all frequency groups used for transmission exceeds a fixed threshold, a first output signal is emitted from the level monitoring switch which releases the data output. If the threshold is again lowered within the specified time, another output signal appears which blocks the data output. Independently of the level monitoring link, the data is evaluated for quality, ie. it is tested whether the code conditions are met.

If the code conditions are not complied with, the recipient will receive an indication of the faulty quality. However, no connection of the level monitoring link with the quality rating link is provided for the secure recognition of the transfer commencement of the data transfer. This known coupling, however, recognizes some of the disturbances that may occur before a transmission commences. Nevertheless, additional disturbances occur which may delay the beginning of a data transfer and are not recognized by the known coupling. For a large number of data transmission systems, in particular in the case of data transmission over the telephone network with exchanges switched on in the transmission path, this means that the data delivery devices cause them to respond during the transmission breaks and give erroneous data '.

It is an object of the invention to provide a coupling with the greatest possible safety against a premixed transmission beginning and to prevent reaction of the delivery devices in the event of a disturbance. This task is solved by the fact that a time-controlled output of the level-monitoring coupling and the output-coupling output is controlled only when a reaction from the level-monitoring coupling occurs during a first defined period and at the same time the first output signal occurs at the output of the utilization-coupling generating a first control signal, which switches switching step to a first switching state in which data delivery devices are released and decoupling the output of the output switch from the control input of the timing link so that the timing is controlled only by the level monitoring switch, the time link when the receiving signal in the level monitoring switch drops below the threshold switch. time, generates another control signal which switches the switching step to another switching state in which the data delivery devices are blocked, and the output switching output is connected to the timing input control.

The coupling has the advantage that it is very cheap and that coupling devices are already used in most data stations. Security against one of the disruptions, false recognition of the beginning of the transmission is great. The invention is based on the basic idea that in many transmission methods there is the possibility that the receiving signal can be derived in addition to the transmitted data types, based on which one can agree on the quality of the received data types and thus on the probability of transmission errors.

Such a known device is referred to as a quality detector. A level monitoring switch determines whether the receive level exceeds a threshold for a specified period of time. During the same period, a utilization coupling (quality detector) provides a criterion for the probability of transmission failure. The two couplings are connected to 4

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a logical interface link whose output signal releases or blocks a data device. The receive level is decreased here after a receive filter, fed to an amplifier and monitored. The utilization circuit either evaluates a prescribed code condition upon transmission, or the demodulated receive signal, i.e. the DC voltage signal, is evaluated according to the demodulator.

DETAILED DESCRIPTION OF THE INVENTION The following is explained by means of a favorable embodiment and with reference to the drawing, in which Fig. 1 shows a frequency diagram of a data transmission system with signaling parallel transmission, and Figs. 2 shows a receiving station for signaling parallel data transmission in the telephone dialing network.

The embodiment shown relates to a device for parallel data transmission in the telephone dialing network, which is referred to as a parallel modem. The term "modem" consists, as is well known, of a contraction of the initial letters of the terms modulator and demodulator. The transmission is by means of multistage frequency modulation and is illustrated in Figure 1 in a frequency diagram.

The parallel data transfer from a terminal station to a central receiving station is done by two or three frequency groups (A, B, C) with each of four frequencies (f1-f4) located in the telephone frequency band. For the transfer of numeric characters, e.g. frequency groups A and C. This means that one frequency is always transmitted from each frequency group, so that sixteen different frequency combinations are available for the transfer of numerical data.

Three frequency groups (A, B, C) are used to transmit alphanumeric data. In this way, one frequency is also always emitted from each frequency group, so that 64 frequency combinations are available for transmitting such data.

The data transfer takes place in two time sections. In the first time section, e.g. the frequency combination corresponding to the characters, while in the second time section the pause combination is transmitted. Of the possible frequency combinations, a particular combination is selected, which after each first frequency combination is transmitted as a pause state. In such a system, by numerical transmission, fifteen frequency combinations with every two frequencies are available for the characters to be transmitted and a pause combination, while for alphanumeric transmission, there are 63 frequency combinations with every three frequencies and a pause combination. Between the signs no levelless state occurs.

1 FIG. 2 is a block diagram of a receiving station for numeric and alphanumeric parallel data transmission. When calling the receiving station from a terminal station over a telephone line FL, a telephone FSP is activated. When operating with an operator, a contact is manually rescheduled, while the contact at unmanned operation is automatically rescheduled to the position shown in the drawing by the phone FSP's reaction. A switch k2 is then in the position shown.

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The received signal is transmitted over a receiver amplifier VE to group filters FI, F2 and F3, which filter out the three frequency groups (A, B, C in Fig. 1). To each group filter is connected a group amplifier (VI, V2, V3), which is designed as a control amplifier with a limiting step. Following the control amplifiers, demodulators D1, D2, D3 are coupled, which recognize the four frequencies (f1-f4) in each group, evaluate these frequencies and convert them to an output signal. Each demodulator contains a filter which is tuned to the frequencies to be recognized, a low-pass filter, a sensing step, preferably in the form of a Schmitt trigger coupling, and an output coupling. In accordance with the frequency combinations, an output signal is always generated at one of the four output wires (1-4) from each group (A, B, C). To the demodulators D1, D2 and D3 is connected a clock generator T, which produces a clock for sensing and transmitting the characters. The sensing rate is available over a line 5. A return signal transmitter RS is controlled over a line 6 for the purpose of sending a "good" or "bad" acknowledgment signal. A voice signal can be transmitted over a line 7 in the return direction, which signal is amplified in a low frequency amplifier FV and reaches the telephone line FL over the contact k2. The contact k2 is then in the dotted position shown.

The dotted line section of FIG. 2 shows the new coupling for secure recognition of the beginning of the transmission. For the purpose of level monitoring, the receiving voltage is taken from the group amplifiers VI, V2 and V3. Namely, the beginning of the transmission is determined by the presence of a frequency in each frequency group (A, B, C). These voltages from the amplifiers are passed to an AND circuit G. To a fourth input of this gate circuit, the output of an exploit switching AS is connected over a decoupling step E. The utilization coupling AS assesses the quality of the received data, which determines the probability of transmission failure.

In the present embodiment, the code condition is tested and, more specifically, each demodulator must output an output signal at the actual beginning of a transmission. On an output line 8, two different signals are generated depending on the result of the code test. An error signal occurs if no frequency or more than one frequency occurs in a group.

If in each frequency group (A, B, G) there is only one output signal, the output signal appearing on the line 8 and a good reception quality corresponding to the decoupling step E to the OG circuit G. If an adequate * receive voltage is present in the the three amplifiers (VI, V2, V3) produce an output signal at the gate circuit which is applied to a timing line ZG. The time step consists in the simplest case of a capacitor and a resistor. At the time point, a bistable coupling step K is coupled with two reaction threshold values, e.g. a Schmitt trigger coupler or a multivibrator. The capacitor in the time line ZG is charged with a certain time constant. When the upper threshold is exceeded, it reacts 6

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bistable coupling steps, and on a line 9, a first control signal is generated which means that there is a transmission beginning and which releases the data delivery device. The first control signal causes, over the decoupling step, that the utilization coupling is separated from the input of the gate circuit. The decoupling step E may be constructed with a coupler transistor or with diodes which pass the first control signal and block the second control signal.

If the level fails in an amplifier (VI, V2, V3) or an error signal occurs at the output of the utilization circuit, since in one frequency group no output signal or multiple output signals occur, the gate circuit G will not be opened and the capacitor in the time converter ZG will be discharged with a certain time constant. When a lower threshold is exceeded, the bistable coupling step K is controlled to the second position. Then, on line 9, a second control signal is generated which means that the level has failed and which blocks the data delivery device. The second control signal controls the decoupling step E such that the output of the utilization coupling is connected directly to the gate circuit G. The error signals appearing on the wires 8 and 9 can be indicated at the receiving station optically or acoustically.

A further improvement can be achieved by monitoring the pause combination occurring at the beginning of a transmission which, as mentioned, is constituted by a particular frequency combination transmitted between two characters. This is done so that the utilization coupling AS over a particular output line only sends a signal of correct reception to the gate circuit G if the interrupt determined for the form of transmission occurs within the time period determined at the time link. Hereby a further improvement of the coupling according to the invention is obtained. Fulfillment of the stated condition through a disturbance will hardly be possible.

Furthermore, there is the possibility to control the output couplings of the demodulators (D1, D2, D3) in a particular state by means of the error signal on line 9 and retain them in this state. It is hereby achieved that interference voltages will not produce any output signals on the output lines (1-4) of the three groups and that the output couplings will only be released at the beginning of a transmission. In this connection, it is advantageous if the output lines give off the break combination. At the beginning of the transfer, the pause state already exists. This causes the output lines to take on a well-defined state and exert no disruptive effects on other wires or appliances and that less requirements may be imposed on the delivery devices.

The new coupling for securely recognizing the beginning of the data transmission in the receiving station can be used in all transmission modes, in which a useful criterion for the transmission signal can be derived from the receiving signal in addition to the information signs.