FR2591051A1 - Method and device for optimising the use of a telephone line of the 4-wire type - Google Patents

Abstract

The device selectively dispatches conversational signals 12 or pure data 13 over the line 1. A detector 34 informs a computation unit 18 of the transmission activity on the channel 12. A delay line 24 grants the computation unit 18 time to decide upon the transmission of conversational signals by controlling a switch 26a. In the absence of conversational signals, a MODEL 21a operates and the switch 26a connects it to the line 1. A remote control circuit 46a transmits a signal representative of the state of the switch 26a so that, at the other end of the line, a receiver switch 26b is controlled correspondingly. Use for preserving good quality of conventional signals.

Description

The present invention relates to a method for using a telephone line of the 4-wire type at each end of which are connected at least a first and a second transceiver equipment, in which, at each end of the line
- the transmission activity of the first equipment is detected and conversational signals transmitted by the first equipment are transmitted in a substantially transparent manner;
- at least one remote control signal is sent as a function of the above-mentioned detection, which is sent to the other end
- depending on the remote control signal received, the useful signal received is routed to the first or the second equipment, depending on whether it comes from the first or respectively from the second equipment of I-other end
By line of the 4-wire type is meant a line comprising a separate channel for each direction of transmission.

In addition, the line can be partially or completely immaterial, and consist for example of a radio link or a satellite link.

By conversational signals is meant signals relating to information changed by users, as opposed for example to signals relating to signaling and / or telephone numbering
The present invention also relates to a device for implementing this method
By "in a substantially transparent manner" is meant to exclude coding, not delays or distortions.

 A process of the above kind is implemented in the CELTIC system marketed by CIT-ALCATEL, which deals with the case where several lines of the 4-wire type are available. This system consists of two concentrating devices, one at each end of the group of lines, to connect these lines to network channels. Each device analyzes the signals arriving by the different channels. When it detects a data transmission, it assigns one of the lines to that transmission until it is completed. When it detects speech2, it assigns a transmission line to each chip, that is to say to each grouping of useful signals between two silences (a grouping lasts on average 750 ms). transmitted only when it includes useful signals, and only in the direction of transmission of the useful signals at all times. The remote control signals are transmitted between the two concentrators by an additional line, called the signaling line, which also serves to convey the signaling and the telephone numbering in a coded form, very economical in time.

 The CELTIC system is suitable for managing a relatively large number of lines. In particular, it requires a signaling line in addition to the lines available for telephone communications. It is based on the statistical observation that n lines are enough to transmit the useful signals conveyed by n + p channels, and it organizes the transmission accordingly, as the signals to be transmitted reach it.

 These initial assumptions are not applicable when it comes to using a single line. One cannot then envisage the presence of an additional line simply to transmit a switching remote control, and on the other hand the aforementioned statistical observations cannot apply. The line would be unoccupied at times, overloaded at other times and the organization of transmissions would be impossible.

 However, the problem of optimizing the use of a single line exists, for example, among users who have rented a line from the Administration.

 In such a case, the user frequently wishes to transmit telephone conversations and computer data or pure data via this line. To solve this problem, the FR-A -2 550 673 proposes to use a vocoder to transform the voice signals into at least two digital signals each occupying a specific frequency range, and to time multiplex one of the digital signals with the data transmitting. On reception, the signals multiplexed on transmission are demultiplexed before between pointers. according to information resulting from the transmission procedure, towards the "synthesis" channel of a vocoder or towards a data reception device. This system therefore allows, without additional signaling line, an optimization of the use of the line, all the more so since the digital signals representative of the voice take less time than the corresponding speech. However, such a system transmits speech only with a quality which is often insufficient. In addition, conversational user stations are capable of transmitting data, for example in the case of fax machines or computer or telematics terminals. The system according to FR-A2 550 673 poses in this regard one problem: the vocoder being incompatible with the transmission of data of the facsimile type, these must be processed by a modulator-demodulator (MODEM) and introduced by the "data" circuit, which requires considerably more expensive equipment.

 The object of the invention is to propose a method and a device which optimize the use of a single line, without degrading the quality of transmission of the voice and without preventing or increasing the transmission of data of the conversational type.

 According to the invention, the method is characterized in that at each end of the line, the second equipment item is put into operation in transmission substantially in the frequency band of the first item of equipment when an absence of emission from the first item of equipment is detected, in that the transmission operation of the second equipment in said band is suspended when the presence of a transmission of conversational signals on the part of the first equipment is detected, and in that the remote control signal is transmitted on the line, at least part of the remote control signal being transmitted in a specific frequency band.

 The first transceiver equipment has priority. It is in principle constituted by equipment of the conversational type. By this is meant equipment which may include, for example, a user station such as a handset and dial dial, facsimile equipment, equipment for conversational correspondence with databases or computers. I1 can also be several such devices connected to a PABX.

 The signals emanating from the first transceiver equipment at one end of the line are transmitted in priority substantially without modification. During this time, the operation of the second equipment in transmission in this frequency band is interrupted. When an absence of activity on the part of the first device is detected, the second device is operated in transmission, for example pure data transmission equipment. In addition, the line is used to convey a remote control signal by which, when an item of equipment transmits at one end, the corresponding equipment is connected in reception to the other end.

For example, if the data transceiver equipment transmits at one end, the remote control signal causes the signals received at the other end to be routed to the data transceiver equipment. Similarly, if the first device puts at one end, the signals received at the other end are routed to the first device.

It will be noted that the step consisting in ensuring the remote control by a frequency channel of the line would not be adapted to the CELTIC system because the remote control signal would occupy a frequency band all the wider as the possible switches are numerous. FR-A-2 550 673 certainly mentions the possibility of reserving a frequency channel for a remote control signal, but without suggesting any function of this remote control In fact, as regards the routing of signals at reception, the FR -A 2 550 673 remains oriented towards the recognition of the nature of the sated signal and in no way suggests using a separate program for the remote control. On the other hand, the FR-A-2 550 673 does not teach either '' interrupt the operation of the second equipment while the first provides a significant signal because the space taken by the digital signals provided by the signals from the vocoder allows the transmission of data at the same time as a bit of speech
According to another aspect of the invention. the device intended to be connected to one end of a 4-wire type telephone line, for the implementation of the above method, is characterized in that it comprises
- - a telephone interface intended to be connected to telephone equipment of the conversational type
- a calculation unit connected to transmission activity detection means at a terminal of the interface
means of input / output of pure data to be transmitted, associated with the calculation unit
- an adder connected to the interface by a transmission channel comprising in series a delay line and between this and the adder, a path going from a first input to an output of a conversational signals / pure transmission data switch
- a transmission remote control circuit connecting the calculation unit to the adder
- a pure data transmission modulator having an input connected to the calculation unit and an output connected to a second input of the switch
- a separator having an output connected to the computing unit by a reception remote control circuit and an output connected to the interface via a path between an input and a first output of a conversational signals / data switch pure reception
- a pure data transmission demodulator mounted between a second output of the reception switch and the calculation unit;
- switches having a control input connected to the caculation unit.

 Other features and advantages of the invention will emerge from the description below.

In the accompanying drawings, given by way of nonlimiting examples
- Figure 1 is an overall diagram of a telephone installation using the invention
- Figure 2 is a block diagram of an optimization device as provided at one end of the 4-wire line in the example of Figure 1;
- Figure 3 represents time graphs of activity at different points of the device of Figure 2
- Figure 4 is a graph of use of the frequency spectrum on the 4-wire line in a direction of transmission during the transmission of conversational signals;
- Figure 5 is a graph similar to Figure 4 but during the transmission of pure data;
- Figure 6 is a diagram illustrating the modalities of transmission of pure data.

 FIG. 1 represents a block diagram of a telephone network using the invention. This network comprises a line 1 of the 4-wire type, that is to say a line comprising a separate channel 1a or 1b for each direction of transmission. Line 1 is installed between two automatic exchanges 2 to each of which are connected to subscriber stations 3. These may include stations for spoken conversation 4, computer systems 6 such as databases, central computer unit etc ... suitable for conversational operation, terminals 7 for conversational access to systems such as 6, fax machines 8, etc ...

 In addition, the two automatic exchanges 2 are interconnected by the entire public switched network 9.

 Each end of line 1 is connected to the local automatic exchange 2 by an optimization device 11 and by a bidirectional line 12 connecting the automatic exchange 2 with the device 11. Each device 11 also has an input / output channel pure data 13.

 The devices there ensure the transmission of communications of the conversational type between two stations 3 located at the two ends of the line 1 and which have been linked to it by the automatic exchanges 2. More precisely, the devices 11 detect the presence of signals useful in each direction of the conversation and selectively connect each channel la or lb of line 1 to lines 12 when the presence of useful signals is detected. In the absence of useful signals in one of the directions, the corresponding channel 1a or 1b is isolated from the lines 12 and connects to the data input / output channels 13.

 In addition, the devices exchange with each other on channel 1 information relating to signaling and telephone numbering which are necessary between the automatic exchanges 2 and between two stations 3 which are in communication through line 1.

 One of the devices 11 of FIG. 1 will be described with reference to FIG. 2, namely the device on the left for which the starting channel is the channel 1a and the arriving channel the channel 1b.

The device 11 comprises a telephone interface 14 of a known type, which is connected on the one hand to the bidirectional channel 12 and on the other hand to a transmission channel 16a and a reception channel 16b by two separate terminals 17a and 17b respectively. The interface 14 ensures the transmission to line 12 of the signals arriving by the reception vote 16b, and ensures according to a known mode (for example according to opinion 3 i64 of
CC ITT) the transmission of the signals received by line 12 to the transmission channel 16a. The transmission channel 16a of the device 11 is connected to the departure channel 1a of the line 1, and the reception channel 16b of the device 11 is connected to the arrival channel 1b of the line 1.

 The pure data input / output channel is connected to a computing unit 18 having an output 19a connected to the input of a fast data transmission modulator Zia and an input 19b connected to the output of a demodulator of fast data transmission 21b. The modulator 21a and the demodulator 21b can be grouped together in the same modulator-demodulator (MODEM).

 The calculation unit 18 is adapted to receive the data by the channel 13 under a determined procedure (for example HDLC). For this, the pure data available under another procedure passes through a procedure adapter 22 which brings them into conformity with the procedure accepted by the calculation unit 18. The calculation unit 18 stores the data received by the channel 13 , and, as a function of detections which will be described later, makes these data undergo certain modifications before delivering them selectively on its output 19a with a view to their transmission by line l to the other device 11. Furthermore, the calculation unit receives on its input 19b the pure data arriving from the other device 11, restores them in the external procedure (HDLC in the example), that is to say made the reverse arrangements to those carried out by the calculation unit of the other device 11 on transmission, and transmits the data thus modified to channel 13.

 The transmission channel 16a comprises in series, in the following order starting from the interface 14, a delay line 24, a low-pass frequency filter 27a, a conversational signal / data switch 26a, and a device 28a summation and access to channel la, hereinafter called summator 28a.

 In particular, the switch 26a comprises an output 29a connected to the adder 28a and which can selectively be connected to a first input 31a connected to the output of the filter 27a or to a second input 32a connected to the output of the fast data transmission modulator 21a by through a low-pass frequency filter 30A which prevents the modulator 21a from sending disturbances into the adder 28a. The switch 26a also comprises a control input 33a connected to the calculation unit 18.

 The reception channel 16b comprises in series in the following order starting from the arrival channel 1b, a reception and separation access device 28b hereinafter called "separator", a conversational signal / data switch Zbb, a pass-by-b-as frequency filter 27b.

 The switch 26b has an input 29b connected to the splitter 28b and can be selectively connected to a first output 31b connected to the filter 27b or to a second output 32b connected to the input of the fast data transmission demodulator 21b via a low-pass frequency filter 30b allowing the demodulator 21b to reach only the frequencies which are useful to it.

 The switch 26b also has a control input 33b connected to the calculation unit 18.

 Thus, the calculation unit 18 can control the switch 26a so that the adder 28a, and consequently the channel selectively receive the signals from the bidirectional line 12 or from the pure data input / output channel 13 In the second case, the calculation unit also functions to extract the pure data from the memory where it is stored and to supply it to the fast data transmission modulator 21a after having arranged it (we will see below what constitutes these arrangements).

 On the other hand, the calculation unit can control the switch 26b to route the signals supplied to the channel 16b by the separator 28b from the channel 1b to the interface 14 or to the demodulator 21b.

 We will now describe the means enabling the calculation unit to decide the control of the switches ba and 26b.

 For this, the device 11 comprises activity detector means 34 comprising a conversational activity detector (speech or conversational data) 38, a numbering signal detector 39 and a signaling detector 41. These three detectors each have a between connected to the interface 14 so that it is sensitive to the signals intended for the terminal 17a, and an output connected to the computing unit 18.

 Thus, the presence or absence of telephone activity on terminal 17a, as well as the nature of this activity on terminal 17a are detected before this activity is delayed by the delay line 24. On the other hand, the switch 26a is located downstream of the delay line 24. The computing unit 18 thus has a delay to decide the state to be given to the switch 26a and to stop the transmission of fast data before changing the state on switch 26a when an activity requiring such a change of state is detected by the means 34.

When the detector 38 indicates to the computing unit the presence of conversational activity (speech, conversational data of the facsimile type, conversational terminal, etc.) on the terminal 17a, the computing unit 18 commands the stopping of the transmission of the data coming from the channel 13, then the passage of the switch 26a in its position connecting the first input 31a with the output 29,
When it detects the start of a speech activity or a conversational data transmission activity, the computing unit, if it is transmitting a frame of binary signals representative of pure data entered by channel 13, proceeds This arrangement consists in terminating the transmission of an inseparable subset of signals (for example a byte), then in sending a supervisory character, then a frame locking character in the procedure between calculation (that of the two devices 11).

 This is illustrated in FIG. 6. At the top of this is shown a frame respecting the external procedure (HDLC in the example}. This frame is limited at each end by a frame locking character 4.

During the transmission of this frame n - l periods of conversational activity were detected by the detector 38. Each time, the computing unit, after having made the decision to transmit conversational signals, completed the elementary frame Ti in transmission course by issuing a supervision character If then a character E for frame alignment of the procedure between calculation units (in accordance with usual practice, the time runs to the left in FIG. 7).

 Each supervision character Si ... Si ... Sn includes information on the nature of the conversational signal which has just been detected (speech or conversational data), and information allowing the remote computing unit to reconstruct the frame of the external protocol from the elementary frames which are transmitted to it. The nature (speech or conversational data) of the conversational signals can be detected by the detector 38. The frame alignment characters A and P are, conventionally, characters serving as a reference point for the transmission equipment. In particular, c It is thanks to the frame alignment characters B that the remote computing unit can find the supervision characters, interpret them for its own use and eliminate them from the frames which are restored to the input / output channel of pure data.

 Thus, the supervision characters inform the receiving computing unit of the nature of the conversational signals which will arrive.

 If the activity which is detected on terminal 17a corresponds to telephone dialing (detector -9) or telephone signaling (detector 41), the calculation unit does not yet take the decision to stop transmitting data and it maintains the switch nua in the state such that its output 29a is connected to its second between 32a. However, the computing unit then proceeds with an arrangement of the data to be transmitted, that is to say that it decides to complete an elementary frame and it includes in the supervision character coded information on the signaling or on the numbering that has been detected. Signaling and numbering can thus be transmitted in a much more time-efficient way than the usual transparent transmission.

A remote control signal generator 46a has a binary input connected to the calculation unit 18 and an output connected to an input of the device 28a. The generator 46a selectively supplies, as a function of the binary signal on its input, two signals of different frequencies but relatively close together and located in the upper part of the frequency spectrum usable on a line of the wire type
In particular, as shown in FIG. 4, these two frequencies use a Btc channel located above that Psc used for the transmission of the conversational signals.

 The device 28a mixes the signals received from the channel 16a and the signal received from the generator 46a.

 The signal received at the input of the generator 46a is determined by the calculation unit 18 so as to be representative of the state of the switch 26a. Thus, as a function of the remote control signal emitted by the generator 46a on the track la of the line l! the remote device 11 is informed of the source of the signals received on the channel 1a, namely the bidirectional line 12 or the pure data input / output channel 13.

 However, between the changes of state of the switch 26a and those of the remote control generator 46a, there are time offsets, explained below, which are managed by the calculation unit 18.

A remote control signal receiver 46b has an input connected to the access and separation device 28b, and a binary output connects to the calculation unit 18. From the remote control signal received via the channel lb of on the part of the signal generator such as 46a belonging to the remote device il, the receiver 46b generates a binary signal intelligible by the computing unit i8. As a function of this binary signal, the computing unit 18 controls the switch 26b so that its input 29b is connected to its first output 31b when the signals received from the remote device it comes from a subscriber station, and to connect its input 29b to its second output 32b when said signals come from channel 13
fi reception of supervision characters
S1 ... S1 ... Sn, the calculation unit 18 recognizes the information relating to signaling and numbering and it produces corresponding input signals intended respectively for a signaling unit 47 and a numbering unit 48 each having an output connected to the interface 14 in the region originating from the channel 16b. These units 47 and 48 reset the signaling and the numbering in the form of the signals usable by the automatic exchange 2 and the subscriber stations 3.

 The device 11 also comprises a noise generator 49 having an input connected to the calculation unit and an output connected to the interface 14 in the reception region.

The noise generator 49 operates in such a way as to produce, while listening on the stations 4, a noise imitating line noise.

Indeed, the fact that, in the absence of a signal useful for understanding, the real communication is cut in one direction or in both directions, constitutes an embarrassment if one has not taken the precaution to introduce a sound effects.

 The device ll further comprises a slow data transmission modulator 52a having an input connected to the calculation unit 18 and an output connected to the summing device 28a. The modulator 52a operates in a frequency band Bdl (FIG. 4) which is relatively narrow and which is interposed between the band Bsc reserved for conversational signals and the band Btc, reserved for the remote control signal. The modulator 32a is controlled by the calculation unit 18 so as to operate when the switch 26a is in its state connecting its output 29a to its first input 31a, that is to say when the switch 26a transmits telephone activity The modulator 52a can be a device allowing a transmission to 300 binary elements per second while the modulator of fast data transmission 21a can be a device allowing a transmission to 4 800 or 9 600 binary elements per second The advantage of the modulator slow data transmission 52a is to allow at least a low data rate in one direction when this direction is occupied durably by a conversational telephone activity, for example during the transmission of faxes Indeed, if there were no possibility data transmission in this direction, data transmission in the other direction may also be interrupted because most of the procedures provide that the good reception of most of the signal groupings must give rise to the emission of an acknowledgment signal. In addition, this low flow of pure data reassures the user who still fears a failure.

 As shown in FIG. 5> the modulator 52a ceases to function when the modulator 21a operates because the latter occupies a frequency range Bdr wider than the range Bsc.

A slow data transmission demodulator 52b has an input connected to the access and separation device 28b and an output connected to the computing unit 18 This demodulator reproduces the slow data received by the channel lb from the modulator such as 52a from the remote device there
We will now set out with reference to FIG. 3 the temporal relationships between various changes of state which may occur in the device.

In graph a, the ACT level corresponds to the presence of conversational telephone activity (speech or conversational data} and the ACT level corresponds to the absence of such activity
In graph b, the DACT level corresponds to the situation in which the computing unit has decided to transmit a conversational telephone activity, and the DACT level corresponds to the contrary The decision to transmit a conversational telephone activity is taken ZI time after the start of the activity to be transmitted.

The decision to interrupt the transmission path of the conversational activity is taken a time Z5 after the cessation of this activity. Z5 is generally larger than ZI (for example five times larger). Indeed, it is generally desirable to consider that the conversational activity begins a certain time (relatively short) before the appearance of useful signals, and that it ends a certain time (relatively long) after the disappearance of the useful signals, this for reasons of comfort of the conversation.

In graph c, the upper level corresponds to the situation where the calculation unit controls the operation of the
MODEM for fast data transmission, and the level lower than the opposite situation From the moment when it has been decided by the unit 18 to transmit a conversational activity, the unit 18 takes the time ZZ to complete the elementary frame in progress From the moment when the unit 18 has decided to interrupt the transmission path of the conversational activity, it allows a time Z4 to elapse before commanding the resumption of operation of the fast data modulator 21a, 21b. This delay Z4 is an inevitable delay of modification of the output of the remote control device after modification of its input.

 In graph d, the oscillations correspond to the operation of MODEM 21a, 2tb and the straight line to its absence of operation. After the instant of the decision to stop the MODEM, it takes a while for Z3 to stop. However, it starts to work very quickly after the decision to put it into operation.

 The graph e shows that the remote control signal as generated by the generator 46a takes one or the other of two frequency levels and changes level at the same time as the graph b.

 The two levels of the graph f correspond to the two levels of the remote control signal as it exists at the output of the remote reception remote control device. As announced above, each change of state is delayed by a delay Z4 with respect to the signal emitted by the transmitting remote control device.

 The two levels of the graph g correspond to the two possible states of the transmission switch 26a. The change of state of the switch in order to start transmitting the conversational activity occurs with a delay Z4 after the decision to transmit taken according to graph b. Consequently, the delay line is chosen to introduce a delay Z equal to Z1 + Z4 so that the conversational activity is transmitted from the start. In this example, Z4 is greater than ZZ + Z3, and this is why the switching is delayed by a time Z4 compared to the decision. Otherwise, the switching would have been delayed from Z2 + Z3 and it would have been necessary slightly delay the transmission of the remote control signal with respect to the decision to transmit, or delay the inversion of the switch on reception, so that at the remote end the reception switch is not reversed too soon.

 at the end of a conversational activity, the decision time Z5 is chosen so that Z4 + Z5 - Z corresponds to the duration whose transmission is to be extended after the end of the activity itself for reasons of listening comfort .

 The graph h symbolizes in the same way as the graph of the operation of MODEM 52a, 52b. The two MODEMs 21a, 21b and 52a, 52b are synchronized by the computing unit so that one stops working when the other starts.

As will have been understood throughout the description, the device according to the invention ensures the substantially transparent transmission of the conversational telephone activity proper (that is to say preferably by excluding telephone signaling and numbering telephone), ensures the transmission of data in the frequency band of the aforementioned telephone activity during the rests of the latter, and also produces a remote control signal mixed in frequency with the useful signal (conversational or data) to switch into the remote device the useful signal to the conver = tional equipment or the equipment for receiving pure data according to the source of the useful signals conveyed at all times
The calculation unit also serves as a buffer memory for storing the data pending transmission.

However, the two calculation units do not have to interact with each other to manage the correct transmission of the data, if the externalization procedure such as
HDLC) to which the computing units are adapted itself includes link control procedures.

 As is known, two MODEM transmitting to each other must be synchronized. To do this, at the start of each data transmission, the transmitting MODEM sends an equalization sequence which is known to the receiving MODEM and on which it can be set.

 Despite this, it can happen that a receiving MODEM loses its synchronization, for example If the conditions on the line change (impulsive noises, micro-cuts, cuts).

To avoid complicating the device li with internal transmission control means enabling it to signal a loss of synchronization and which, moreover, are ineffective when a line is disturbed in both directions, it is provided according to the invention that the The calculation unit interrupts and then re-establishes at regular intervals (for example every five seconds) the transmitting MODEM to cause the latter to send a synchronization sequence.

When there is neither telephone activity nor pure data to be transmitted, the calculation unit controls the modulator 26a so that it permanently transmits characters
B (Figure 6). Everything is ready to transmit pure data or telephone signaling as appropriate.

The invention provides a compromise between the speed of transmission of the conversational signals (minimization of the delay lines) and the efficiency of the transmission of the pure data during the silences of the conversation. This is ensured by the procedure of elementary frames, which allows a so-called valid transmission without having to wait for the end of a global frame,
Thanks to the remote control on a specific frequency channel Btc, there is no risk of confusion between the remote control signals and the signals from channel 12 (whose nature is relatively unpredictable as sent by users) during transmission conversational telephone activity on
Of course, the invention is not limited to the examples described and shown, and numerous modifications can be made to these examples without departing from the scope of lwinventionX
For example, it could be provided that only the remote control signal announcing the end of a conversational signal and the start of a pure data signal passes through the remote control frequency channel The remote control signal announcing the end of the transmission of pure data and the start of the transmission of the conversation could be integrated into the supervision character of the last elementary frame supporting the pure data.

 In certain embodiments, the calculation unit could integrate some of the functions which, for explanatory purposes, have been taken out in the example described and represented. It therefore goes without saying that according to the present invention, the term calculation unit is aimed at a certain set of functions and not necessarily a set materially separated from the other components of the device.

Claims (12)

REYENDICÀTIONS t. Method for using a 4-wire type telephone line at each end of which are connected at least a first transceiver device (2, 3, 4, 6, 7, 8) and a second transceiver device (21a, 21b) , in which, at each end of the line (1) - the transmission activity of the first equipment is detected and the conversational signals put in by the first equipment are transmitted in a substantially transparent manner - it is produced as a function of the aforementioned detection at minus a remote control signal that is sent to the other end - depending on the remote control signal received, the useful signal received is directed to the first or second equipment, depending on whether it comes from the first or respectively from the second equipment of the 'other end, characterized in that at each end of the line: - the second equipment is put into operation in transmission substantially in the frequency band (Bsc) of the first equipment when an absence of emission d is detected e on the part of the first device - the transmission operation of the second device in said band (Bsc) is suspended when the presence of a transmission of conversational signals from the first device i is detected and - the remote control signal is transmitted to line (1), and at least part of the remote control signal is transmitted in a specific frequency band (Btc>.  2. Method according to claim 1, characterized in that when the transmission operation of the second equipment is interrupted, information to be transmitted by the second equipment is stored in memory, and when the second equipment is operated (21a, 21b ) in emission, the emission is worked out according to the information in memory  3. Method according to one of claims l or 2, characterized in that at least one of the ends, one transmits on the transmission by one of the equipment a transmission in a frequency band (Bdl) offset from to the frequency band of the useful signal (Bsc, Bdr) and relative to the band (stucco) specific to the remote control.  4. Method according to one of claims t to 3, characterized in that the transmission activity detection of the first equipment comprises a telephone signaling detection, and in that when a telephone signaling is detected, the second equipment is operated ( 21a, 21b) to transmit this signaling in coded form.  5. Method according to claim 4, characterized in that the second equipment transmits data in successive frames (Ti .... Ti. ... Tn)! and in this case when using in at least some of the frames a location (Si .... Si ... Sn) for the coded transmission of the telephone signaling and / or dialing.  6. Method according to one of claims 1 to 5, characterized in that at each end at least some of the signals transmitted by the first equipment are delayed after having subjected them to the detection of transmission activity.  7. The method as claimed in claim 6, characterized in that, when a start of activity of the transmission of conversational signals from the first device is detected at one of the ends of the line, it is emitted from this end, in the substantially common frequency band (Bsc, Bdr), during the delay given at the start of the conversational activity, a signal representative of this activity.  8. Method according to claim 7, characterized in that at each end of the line, at least at the start of an activity originating from the first device, it is detected whether this activity consists of speech or of conservation data, and transmits this information to the other end by means of the aforementioned representative signal.  9. Method according to one of claims t to 8, characterized in that, the second equipment (21a, 21b) being a data transmitter-receiver equipment, data is received in global frames and at least some of the global frame in elementary frames (Ti .... Ti ... Tn) when the transmission of data on the line  (1s is interrupted by the transmission of signals from the first device  10. Method according to claim 9, characterized in that at each end, at least at the start of a transmission of conversational signals by the first equipment, these are delayed by a duration which is sufficient to complete an elementary frame (Ti ... Ti ... Tn) according to an internal protocol before starting the transmission of signals from the first device.  it Method according to one of claims 9 or 10, characterized in that a supervision character (si..Si ... Sn) is inserted into each elementary frame (Ti ... Ti ... Tn), and in that on reception of the signals transmitted by one of the second devices, a reconstructs the global frames by grouping the elementary frames according to information provided by the supervision characters.  12. Method according to one of claims l to 11. wherein, during a transmission between two MODEMs (21a, 21b) each belonging to one of the second devices, a synchronization sequence from the sending MODEM to the receiving MODEM is sent at fixed time intervals.  13. Device intended to be connected to one end of a 4-wire type telephone line, for implementing the method according to one of claims 1 to 12, characterized in that it comprises  - a telephone interface (14) intended to be connected to telephone equipment of the conversational type  (2 to 4, 6 to 8);  - a calculation unit (18} connected to means (34) for detecting the transmission activity at a terminal (17a) of the interface (14);  - data input / output means (13) to be transmitted associated with the calculation unit (18) 5  - an adder (28a) connected to the interface (14) by a transmission channel (16a) comprising in series a delay line (24) and, between the latter and the adder, a path going from a first input ( 31a) at an output (29) of a conversational signal / pure data switch (26a);  - a transmission remote control circuit (46a) connecting the calculation unit (18) to the adder (28a);  - a pure data transmission modulator (21a) having an input connected to the computing unit (18) and an output connected to a second input (32a) of the switch (26a);  - a separator (28b) having an output connected to the computing unit (18) by a reception remote control circuit (46b) and an output connected to the interface (14) via a path between an (29b) and a first output (31b) of a conversational signals / pure data switch (26b);  - a pure data transmission demodulator (21b) mounted between a second output (32b) of the reception switch (26b) and the calculation unit (18);  - the switches (26a, 26b) having a control input (33a, 33b) connected to the calculation unit (18).  14. Device according to claim 13, characterized in that it further comprises a slow data transmission modulator (52a) having an input connected to the calculation unit (18) and an output connected to the adder (28a), and a slow data transmission demodulator (52b) having an input connected to the splitter (28b) and an output connected to the computing unit (18).  15. Device according to one of claims 13 to 14, characterized in that the activity detection means (34) comprise signaling / telephone numbering detection means (39, 41), and in that the device comprises furthermore signaling / numbering generator means (47, 48) having an input connected to the calculation unit (18) and an output connected to the interface (14,) being the calculation unit (18) to transmit the signaling / numbering on line (1) in coded form.