FR2699030A1 - Automatic duplex or half-duplex momomode or multimode communication between two telephone units - Google Patents

Abstract

The communication method between two switched telephone units involves exchanging matching signal streams. A fast equipment sends out the matching signal in half duplex. The second equipment, on recognition and validation of the validation segment, emits a second signal in the recognised mode. The first equipment analyses the second signal, and if it recognises the signal it stays in the accepted mode for reception and sets up the communication. If the second transmission mode is slower, the second equipment does not recognise the first mode. In this situation, the roles of the equipment are reversed, and the validation procedure occurs w.r.t. the previous sequence but in the second mode of transmission.

Description

METHOD OF RECOVERY ADAPTATION FOR
MAINTAINING DUPLEX COMMUNICATION IN THE ALTERNATE
BETWEEN TWO EQUIPMENTS THROUGH A LINE
TELEPHONE.

 The present invention relates to a method that allows the maintenance of the duplex communication in the presence of alternating disturbances of the telephone line.

Since July 1, 1980, date of the first experimentation of the Directory service
Electronics in Saint-Malo, the "Minitel" uses, in
France, a transmission rate of 1200 bits per second to receive the information of services consulted and a speed of 75 bits per second to transmit the input of the user. This mode of transmission, in full duplex ("full duplex") is based on the V23 modulation namely a speed of 1200/75 bits / s between the equipment "Minitel" and Access Point
Videotex ("PAVI"). The connection between the "Minitel" and the "PAVI" is based on the switched telephone network ("PSTN"). The link between the "PAVI" and the servers (Teletel "relies on the" TRANSPAC "network with transmission speeds of 19.2 Kbps or 48 Kbps.

In the early 90s, in order to improve the comfort and speed of consultation of "TELETEL" services, it was planned to increase the transmission speed first to 4800 bps and then to 9600 bps between
Access Point and "Minitel". This new half-duplex transmission mode is based on the V27ter modulation for 4800 bps speed and on the so-called V29 modulation for 9600 bps. Standards
V27ter and V29 (see fax group 3) were selected for reasons of cost and performance. The 4800 bps and 9600 bps speeds can be used on both channels, with the modem running in alternate mode.

 This new "Télétel" access service, called "Fast Speed Teletel" access service (TVR), allows a useful communication rate multiplied by four (in the case of the V27ter) and by eight (in the case of the V29) compared to the useful rate of access V23.

 During the establishment of the communication, by giving priority to the transmission mode according to the fastest modulation such as V29, an optimum transfer of pages requiring an important volume of information is allowed; it is the privileged channel for the operation of the future photographic "Minitel" and for file transfer applications.

 In general, the switched telephone network ("PSTN"), initially designed for the transport of the speech signal, is subject to disturbances of various origins which, if they have a negligible influence on the quality of the telephone service, have consequences very important on a transmission service.

The network structure is relatively complex and implements a wide variety of equipment. Disturbances, especially in the form of impulsive noise, come for example from crosstalk, impulses from charging systems or episodic desynchronizations between the switches. In addition, some high speed (2 Mbps) digital links between switches (links
MIC) can, in case of overload of the link, increase the number of simultaneous communications in a ratio of 2 (MIC.DA process) by compressing the transmission. This method, well adapted to telephony, disrupts the continuity of communications in the V29 modulation.

 The disturbance caused by impulse noise introduces effects that vary according to the data modulation principle used. According to the V23 standard, one generally obtains 1 false bit in line; this type of error is recovered by setting up a known error correction procedure.

 The aim of the invention makes it possible to implement, in the case of duplex duplex communications, for example V27ter and V29, a protocol making it possible to maintain and resume communication at the physical level, without disconnecting so-called "higher" levels. "(packets and frame). The basic idea of the invention is to implement this protocol in the form of a method of readaptation.

In the context of the V27ter phase differential modulation and even more in the context of the amplitude and phase combined modulation of the V29 standard, for example in the case of impulsive noise, there is propagation of the error on several consecutive bits, especially since the signal is subjected to a stirring step propagating the decoding errors; in fact, in order to break the too long series of o and 1, the modems are equipped with a scrambler-descrambler of polynomials generator 1 + x 6 + x-7 in standard V27ter and 1 + x-18 + x -23 in standard V29.De fact, the V27ter modulation of DPSK type (Differential Phase Shift Keing) is more "robust" than QAM type V29 modulation (Quadrature
Amplitude Modulation) with respect to disturbances due to the telephone network.

 The Télétel network is architected in such a way that the Minitel and Pavi facilities are connected by short-distance telephone links. Measurement campaigns carried out by the Applicant have shown that the majority of so-called short local links of the switched telephone network has stationary transmission characteristics (such as attenuation, distortion of group time) and only occasionally suffers disturbances, mainly impulsive noise type. In fact, although we prefer the V29 modulation which is optimal for most communications, it appears essential to set up mechanisms for maintaining communication when this modulation will be weakened to the point of breaking communication.

 Given the short-line hypotheses, we used a first mechanism for freezing the coefficients of the modem's reception filter. The values of these coefficients are fixed during the establishment of the communication, after a first exchange of long learning sequences or train of agreement signals which allows in particular the two modem equipment, depending on the characteristics of the support of transmission to effect the convergence of the coefficients of their reception filter, to avoid any uncertain and uncontrollable fluctuation of these coefficients, to each short learning sequence received during communication. In fact, half-duplex data transmission is based on exchanges of short training sequences or synchronization signal streams, whether or not they carry application information. It has proved important not to modify the filter coefficients during the exchanges of the synchronization signal trains, although the standard allows it, because this mechanism causes a rapid mismatch of the modems during the appearance of disturbances in line. eg impulsive noise.

 The mechanism for freezing the coefficients during the exchange of tuning signal trains allows better control of the transmission efficiency by the reliable and faster detection of erroneous synchronization signal trains. In fact, in order to allow a new adaptation of the modems at the level of the reception filter coefficients, as a function of the new characteristics of the transmission line, a second so-called resumption mechanism is implemented to cause a new exchange of signal trains. of agreement. This method can be used in duplex transmission modes such as V27ter, V29, V17. I1 is based on the presence of segments 1 & 2 of the tuning signal trains thus enabling their identification during communication. The originality of this method allows resynchronizations reliable at the physical level without altering the higher logical levels of the protocol. communication, which allows to continue the transmission without breaking at the application level, although the physical medium is altered.

In addition, in the case where the transmission mode uses the V29 modulation, in case of failure of the recovery method described above, a third mechanism for maintaining the communication by changing the type of modulation is implemented. This method of changing the speed of change by type of modulation makes it possible to continue the transmission without breaking at the application level by using a more robust modulation, such as modulation.
V27ter, compared to the V29 modulation.

More generally, the method of "adaptation resumption combines the three previously mentioned mechanisms namely
adaptation of the type of modulation, in particular by freezing (or freezing) coefficients of the reception filter
- resumption of transmission
- possibly, fallback speed (such as
V29 to V27ter).

In a known manner, the modem speed-down modes, as provided for example by the CCITT standards V27 ter, V29 and V17, consist in reducing the speed of modulation by reducing the number of states without changing the type of modulation. modulation. This fallback mode does not provide a satisfactory result, especially in the case where the communication medium is affected by impulsive noise and it is used in practice only for certain equipment of lower speed. The recovery-adaptation method aims at to overcome these drawbacks of the being of the technique, by allowing a fallback in a less rapid modulation, but more robust with respect to the disturbances originating in particular from the evolutionary and / or unstable characteristics of the telephone line, or which originate a compression of the flow rate of the transmission (cf.
MIC.DA supra).

 It has been possible to implement the speed fallback mechanism through the presence of the segments 1 & 2 of the long learning sequences that not only allow the recovery mechanism in the same modulation during communication but also the velocity foldback mechanism by distinction of the signal carried by said segment 1, characteristic of the type of modulation. This process can be repeated for transmission modes such as V17, V29, V27ter.

 It should be pointed out that in terms of useful throughput, by favoring the fastest mode of transmission according to the least robust modulation type, the compromise "useful rate / duration of the communication" is solved by the possibility of not being forced to break the communication in case of major and fugitive disturbances and the ability to adapt the speed of modulation when the transmission medium temporarily has less favorable characteristics, this without interruption at the application level.

The invention thus relates to a resumption-adaptation method for at least one duplex modulation alternating between two equipment A and B through a telephone line, characterized in that it uses, during exchanges of synchronization signal train possibly followed by application information, an exchange of signaling signals at the initiative of one of the equipment called first equipment for the resumption-adaptation, preferably following the detection by it at least two successive trains of erroneous synchronization signals, each tuning signal stream starting with an unmodulated carrier signal of given nominal duration having a carrier frequency characteristic of the transmission mode, the other equipment being referred to as second equipment for resumption-adaptation, in that each of the two equipment A and B is arranged to detect the frequency of said signal unmodulated carrier and in that the first and second equipment are arranged to perform the exchange of two tuning signal trains according to the following steps
a) initialization by the first equipment of a resumption-adaptation, preferably following detection by the first equipment of at least one train of erroneous synchronization signals, and preferably two erroneous successive trains.

 b) transmission by the first equipment of a tuning signal train according to the transmission mode previously used in duplex duplex for the exchanges of synchronization signal trains.

 c) analyzing by the second equipment the frequency of the unmodulated carrier signal of said tuning signal stream.

 d) in the event of recognition of this frequency characterizing a request for adaptation resumption, positioning of the second equipment in reception of a train of tuning signals.

 e) in case of validation by the second equipment of the reception of said tuning signal stream, adaptation of the second equipment according to said transmission mode used, preferably by freezing of the reception filter coefficients adapted to the new characteristics of the support medium; transmission.

 f) transmission by the second equipment of a train of tuning signals according to the recognized transmission mode.

 g) analyzing by the first equipment the frequency of the unmodulated carrier signal stream of said tuning signal stream.

 h) in case of recognition of this frequency, maintaining the positioning of the first equipment in reception in said transmission mode.

 i) in case of validation by the first equipment of the reception of the train of tuning signals transmitted by the second equipment, adaptation of the first equipment according to said transmission mode, preferably by gel coefficients of the reception filter of the first equipment .

 j) resuming the exchanges of synchronization signal trains, possibly followed by application information without breaking the higher logical levels of the communication protocol of the two devices.

Said initialization can be carried out at the initiative of the higher levels of the protocol (frame-packet) to attempt a synchronization mode
V29 of a transmission folded in V27ter (on detection of a low or no number of defective CRC codes). This case can occur especially in case of overload termination of a MIC-DA transmission. A so-called initialization can also intervene on the initiative of the application itself. An initialization allows the modem to be in transmission mode of a long train.

According to one embodiment for maintaining communication in a fallback mode (case ne12), the method according to the invention is characterized in that the first and the second equipment are arranged to manage at least one second mode. duplex transmission (for example
V27ter) slower than the initial transmission mode (for example V29) but more robust with respect to the in-line disturbances and in that the first and the second equipment are arranged to perform after the steps a) to g) the following steps
k) in case of non-recognition by the first equipment of the train of tuning signals emitted by the second equipment, and possibly after a given delay time, transmission by the first equipment of a signal train of in the second mode of transmission.

1) Analysis by the second equipment of the frequency of the unmodulated carrier signal of said train of tuning signals transmitted by the first equipment
m) in case of recognition of said frequency during step 1), which then characterizes a request for adaptation resumption in the second transmission mode, positioning of the second equipment in reception of a tuning signal train according to the second mode of transmission.

 n) in case of validation by the second equipment of the reception of said tuning signal stream, adaptation of the second equipment to the second transmission mode, preferably by freezing of the reception filter coefficients adapted to the new characteristics of the transmission medium and adapted to the second transmission mode.

 o) transmission by the second equipment of a tuning signal train according to the second transmission mode to allow the first equipment adaptation of the second transmission mode.

 p) analyzing by the first equipment the frequency of the unmodulated carrier signal of said tuning signal stream transmitted by the second equipment.

 q) in case of recognition of this frequency, maintaining the positioning of the first equipment in the second transmission mode used.

 r) in case of validation by the first equipment of the reception of said tuning signal stream transmitted by the second equipment, adaptation of the first equipment to the second transmission mode, preferably by freezing the reception filter coefficients to be adapted the new characteristics of the transmission medium.

s) recovery, according to the second transmission mode, of the exchanges of the synchronization signal trains, (for example short trains in
V27ter), possibly followed by application information without breaking the logical levels of the communication protocol of the two devices
The method according to the invention can also make it possible to manage the case where the readaptation protocol does not meet the success at a first attempt, either from an initial high speed modulation (V29, see case ne11, or else
V27ter cf. case ne10) (but without the possibility of a fallback modulation), either from an initial fallback modulation after a successful previous re-adaptation procedure (case ne10).

For this purpose, the method is characterized in that the first and the second equipment are arranged to perform the following steps after steps a) to g).
t) in the event of non-recognition of the signaling train by the first equipment, possibly after a given delay time, renewal by the first equipment of the transmission of the agreement signal stream according to said transmission mode.

u) steps c) to j)
It can also be characterized in that it comprises the following step (cases # 12bis and # 13)
v) in case of non-recognition by the first equipment, during step g of said sequence u) of the train of agreement signals transmitted by the second equipment, and possibly after a given time delay, last attempt made by the first equipment according to t) and u) before breaking the link between the two devices.

 According to a preferred embodiment, the method is characterized in that the equipment is arranged, after reception of the tuning signal trains, to freeze the coefficients of their reception filter after convergence of the coefficients of said reception filter and in that that the equipment is arranged to inhibit any possible modification of the reception filter coefficients during the exchange of the synchronization signal streams during communication so as to maintain, independently of the characteristics of the physical transmission medium, the values of the coefficients of the filter received at the reception of the last train of tuning signals. This can be implemented during a recovery-adaptation procedure in the same transmission mode or in a fallback modulation.

 According to the invention, the carrier signal is characterized in that the unmodulated carrier signal is an echo protection segment used on the satellite links. This allows, without modification of the modem equipment, the maintenance of the physical recovery-adaptation communication in the same modulation or in a fallback modulation. The frequency of this unmodulated carrier signal becomes characteristic of a resumption-adaptation request. The signal, during communication and in the presence of evolutive and / or unstable characteristics of the physical medium (telephone line), allows a new adaptation of the equipment strictly to the physical level without disruption or intervention of the higher logical levels (frame, packet) of the protocol Communication.

 According to an advantageous variant, said validation of the setting in communication by the equipment comprises the transmission of a synchronization signal train not starting with an unmodulated carrier signal in order not to degrade the useful rate during communication. . This makes it possible to validate the reception of the second set of agreement signals exchanged according to the transmission mode adapted to the two devices.

The invention also relates to equipment for carrying out the above method and comprising a processing unit, a modem, a line interface and a control bus between the processing unit and the modem, the control unit. having a sequence for sequentially programming said modem, characterized in that said sequencer is arranged to
10-1) program the initiation of a resumption-adaptation, preferably following the detection of a reception by the modem of an erroneous synchronization signal stream, without modifying the values or coefficients of the reception filter.

 10-2) programming the transmission by the modem of a tuning signal stream preceded by an unmodulated carrier signal, preferably according to the same modulation as said erroneous signaling signal stream, said setting signal train in agreement constituting a request for resumption-adaptation.

 10-3) schedule the modem to detect at least one unmodulated carrier frequency at the beginning of a received tuning train, and to position the modem in a corresponding duplex transmission mode at said carrier frequency, so as to enable the modem to detect a resumption-adaptation request to receive the other signals of said received tuning train and to freeze the reception filter coefficients after reception of the tuning train.

 10-4) validating the duplex physical matching recovery according to said transmission mode once the modem has transmitted and received in accordance with said signaling signal stream during a communication by exchange of train tuning signals, which then allows the equipment to exchange trains synchronization signals (short trains).

 The sequencer can be arranged so that, when the modem is in reception mode, said detection of at least one unmodulated carrier frequency is carried out continuously and in the event of such detection carried out while the equipment is in a configuration duplex communication system, as well as receiving in accordance with a tuning signal stream, programming the transmission by the modem of a tuning signal stream preceded by an unmodulated carrier signal, according to the same modulation as said tuning signal stream received conformally and validate a resumption-adaptation according to this same modulation.

 It can also be arranged to validate said transmission of a signal stream according to 10-2 when the modem has detected at least one synchronization train in a main transmission mode, to perform at least one attempt to implement agreement according to the main transmission mode and in case of failure to validate a said transmission of a 10-2 compliant signal stream in a fallback transmission mode in a more robust half-duplex modulation as the modulation of the main transmission mode.

 According to another variant, it can be arranged to validate said transmission of a tuning signal stream in a main transmission mode, to perform at least one attempt to match according to the main transmission mode, to perform least one attempt to match according to the main transmission mode and in the event of failure to validate a so-called transmission of an agreement signal stream according to step 10-2) in a fallback transmission mode according to duplex modulation more robust than the modulation of the initial transmission mode.

 The sequencer is preferably arranged to handle the higher logic levels of the communication protocol with a disconnect delay of longer duration than the execution of the resumption-adaptation process. In V27 and V29 modes, the standard provides a level 2 repetition delay (frame) that is reset when a frame is transmitted.

This delay (2.5 s) increments a re-transmission counter in the event of erroneous train detection or no detection. The maximum value of this storyteller can be modified, its nominal value being 10. With this value and in the worst case of re-adaptation, the maximum limit is never reached, and the transfer is only momentarily slowed down without interaction. with level 3 * (package).

Other features and advantages of the invention will appear better on reading the following description, given by way of non-limiting example, in connection with the drawings which represent
FIGS. 1a and 1b, respectively, a block diagram of a "TELETEL" type transmission network illustrating different types of equipment and access points and a block diagram of a card fitted to a terminal and implementing a DCE component (technical data communication equipment) or "modem" programmable by bus and used to implement the invention,
FIGS. 2 to 20, cases 1 to 9 and 14, corresponding to different connection configurations, cases 10 to 13 corresponding to resumption-adaptation configurations and cases 15 to 20, to given voice switching configurations, the calling equipment being in the left-hand column, and the equipment called in the right-hand column, - FIGS. 21a to 21s for the R96-VFX modem, respectively, its programming in V29 (21a) mode and in V27ter (21b) mode. , the freezing of the coefficients of its filter (21c), its programming in short train mode (21d), its programming in transmission mode (21e) or reception (21f) of a short train or a long train, in V29 modulation or V27ter, its programming in frequency transmission (21g), successively for the programming and the emission of a frequency and for the stop of the emission of a frequency (2lh), its programming in mode of detection of frequencies ( 21i), the programming coefficients of the filters FR1, FR2 and FR3 for the det ection of frequencies with the RAM address of the coefficients according to the filters (21j), and the integration constants of the filters (21k), the detection of the 2100 Hz (211), the detection of the 1300 Hz (21m) , the detection of the 1800 Hz (21n), and the detection of the 1700 Hz (21O), the writing procedure in the RAM RAM of the modem (21p), the detection of a frequency with a filter (21q) , the validation of the segment 1 (unmodulated carrier) in the given mode (21r) and the validation of the segments 3 and 4 (short train or long train) (21s).

FIGS. 22a to 22d, a transmission sequence respectively of a long train V29, a long train V27ter, a short train V29, and a short train V27ter, SI designating a unitary interval according to the standard ,
FIGS. 23a to 23d, a reception sequence respectively of a long train V29, a long train V27ter, a short train V29, and a short train V27ter,
FIGS. 24a to 24d, an end-of-transmission sequence respectively in long-wave mode V29 (24a), in long-wave mode V27ter (24b), a data transmission and end-of-transmission sequence in train mode. short V29, as well as V29 long train in case of recovery (24c), and a sequence of data transmission and end of transmission in V27ter short train mode, and V27ter long train mode in case of recovery (24d),
FIGS. 25a to 25f, an end of reception sequence respectively after a long train V29 (25a), after a long train V27ter (25b), a sequence of reception of the flags and data and the end of reception in short train mode V29 (25c), in the V27ter (25d) short train mode, in the V29 (25e) long train mode and in the V27ter (25f) long train mode,
FIG. 26a, an equipment communication automaton (calling mode and called mode) being understood that a particular piece of equipment can implement the two modes, or only one of the modes, and FIG. 26b the beginning of FIG. connection controller (line socket) in both modes.

FIGS. 27a to 27g, the calling-up connection automaton and implementing elementary sequences of FIGS. 22a to 25f,
FIGS. 28a to 28e, the called mode connection automaton of FIG. 26 and implementing elementary sequences of FIGS. 23 to 25,
FIGS. 29a to 29c, a data switching automaton given and implementing elementary sequences of FIGS. 22a to 25f,
FIGS. 30a to 30d, an adaptive communication and revision-adaptive autmate
V29 (30a and 30b) and V27ter modulation (30c and 30d) and implementing elementary sequences of Figures 22a to 25f.

In FIG. 1A, videotex 14, audiotex (voice) 15, videotex and photographic servers 16 connected to the TRANSPAC network, are accessible to users 1 to 6 by the switched telephone network through videotex access points (PAVI), V23 (asynchronous 7 bits plus parity bit for example numbering 3614 or 3615 in France) or in
V27ter and / or V29 (8-bit synchronous). A terminal (V23) for example microcomputer V23 1 or Minitel V23, 2 can only access a PAVI V23. On the other hand, a multimode terminal, for example Minitel 3 (V23 / V27ter) or 4 (V23 / V27ter / V29), microcomputer 5 (V23 / V27ter / V29) or Access Service Microcomputer 6 V23 / V27ter / V29, may have access to all PAVIs. A single mode terminal
V27ter or V29, for example a microcomputer 5, can have access to a corresponding PAVI V27ter or V29.

 The terminal 6 allows in particular a file transfer application (STUTEL) and secure (LECAM: Memory Card Reader 1200 or 4800/9600 bps). The invention therefore proposes a method for automating connection procedures for single-mode or multimode operation in at least two modes.

The method according to the invention, while having the same behavior as V23 connection "MINITEL""fullduplex" allows and optimizes the connection of "Minitel" (backward compatibility) on TVR accesses (V27ter Fast Speed Terminal and / or
V29) and on accesses V23, without any particular action of the user (key Connection-End), by automatic distinction of the speed of transmission. The distinction between two modulations or three modulations is based on one or the other of two discriminants, one to differentiate the fast speed from the normal speed (V23), the other to separate the two modulations selected in fast speed (V27ter / V29).

1) Physical establishment of communication
During the automatic response operation, the echo suppressors are neutralized by the 2100 Hz response tone (see recommendation
V25 of the CCITT). The presence of this tone is justified for full-duplex or partial duplex transmissions such as V23. On the other hand, in duplex half-duplex transmission as in V27ter and V29, the echo protection devices are restarted by a signal silence (silence) equal to or greater than 100 ms. . In half-duplex or full-duplex transmission (V23), the neutralization of these devices is maintained by the reappearance of the signal before the expiration of a delay of 75 ms + or - 20 cms. The provisions of the standards are only relevant in the case of a satellite link.

This difference in the duration of silence is used, according to the invention, to differentiate the V23 mode, V27ter modes and V29 (first discriminant). The specified values are as follows: silence of 75 ms + or - 20 ms for V23 mode, - silence of 150 ms + or - 20 ms for fast speed mode V27ter / V29.

This first discriminant needs to be implemented only for equipment likely to access networks according to the different types of duplex link.

 It should be noted in particular that the equipment according to the invention can be provided for example only to operate in V27ter and / or V29.

The first discriminant can be implemented alone for equipment intended to operate in
V23 and in V27ter mode, or in V23 mode and in
V29, in the case of so-called normal connection anticipated.

The second discriminant, which makes it possible to identify two half-duplex operating modes according to two different rates, for example, between the V27ter and the V29, is, according to the invention, the frequency of the signal of the carrier which is 1800 Hz in V27ter and 1700 Hz in V29.

According to the invention, a signal at the frequency of the unmodulated carrier is sent at the beginning of the long learning sequence (long train). The equipment receiving this signal detects its frequency and can automatically position its modem in the required mode (matching) or find that it can not operate in the modulation with this carrier frequency. A long learning sequence thus fulfills, according to the invention, the function of matching the two devices on the same modulation.

According to a preferred embodiment, discriminating segments used for echo suppression in the satellite links are used.

Indeed, these segments implement a transmission of the unmodulated carrier for a period of 185 to 200 ms followed by a silence of 20 ms at the beginning of long learning sequence (long train); this issue corresponds to segments 1 and 2 as described in CCITT recommendation V27ter and V29. In the prior art, the presence of these segments in advance of the training sequences corresponds to the "speaking" mechanism on the satellite links; indeed, the echo suppressor devices use threshold detection systems that have a significant response time; it is to guard against this response time that the "speaking" mechanism, based on segments 1 and 2, is used in a satellite link.

The invention takes advantage of the recognition that the duration of the segment 1 (185 to 200 ms) is compatible with the programming time of a modem, and in particular of its reception filter, which allows the intended application .

The speaking mechanism available by the presence of the segments 1 and 2 is thus according to the invention deviated from its primary function to be used as a V27ter / V29 discriminant. Modulations
V27ter and V29 use different carriers: the carrier frequency in V27ter is 1800 Hz and that in
V29 is 1700 Hz. Because of its ability to reliably detect tones by digital filtering, the DCE component (or modem) makes it possible, during the initial connection, as will be described later, to distinguish these two frequencies when the long learning sequences are transmitted with the segments 1 and 2. This therefore makes it possible to program the modem in the mode chosen (in agreement), to receive correctly the corresponding long learning sequence. According to a preferred mode, a sequence long learning can only be validly received if its carrier frequency (segment 1) has been recognized by the receiving modem. If the carrier frequency is not recognized, the training sequence is detected as non-compliant. The modem of a device is programmed to recognize the carrier frequency of the modulations that it can receive and transmit (for example a device that can not operate in V29 does not necessarily recognize the frequency 1700 Hz, which allows an effective discrimination of various cases as will be described later). According to the invention, the segments 1 and 2 are, however, not used in the short training sequences (synchronization) transmitted to each modem reversal to not slow down the useful rate of communication.

It will be recalled that the exchange of data is done in packets. A packet transmitted in one direction is preceded by a short learning sequence (synchronization). After receiving the packet, the two modems are "turned over", so as to exchange their transmission-reception functions, and a packet is transmitted in the other direction, preceded by a short training sequence, and so on.

2) Physical recovery during communication
The mechanism based on the presence of segments 1 and 2 allows to implement the voice-data switching process. This alternation of use of the phone line in voice mode and given mode is currently available on the models M10-M12 (V23 modulation) of "Minitel" equipped with an integrated telephone.

For the V27ter and V29 modulations, when returning to connected mode (or data mode), the use of the same process with the transmission of long learning sequences (and the presence of segments 1 and 2) makes it possible to reliably manage the recovery. physical communication in the appropriate modulation V27ter or
V29 with test in the fastest modulation. The application software must in this case manage a context for the V23 or V27ter / V29 telematic communication recovery mode in the absence of the discriminant normal speed / fast speed (duration of silence). Moreover, in fast speed mode, unlike recovery and fallback processes, the communication software must completely restore the different higher levels (connection frame and call packet).

For the record, recall that according to the prior art, in V23 mode, the "reconnection" is of simplified type by detection of 600 ms at least 1300 Hz without seeking the frequency 2100 Hz; the error correction procedure is activated by the user.

The automatic processes of physically establishing the call and restoring during a call make it possible, according to a preferred embodiment, to establish automatically the connection in the three modulations and the returns in connected mode for the voice application. given.

The voice-data application known per se in V23 is renewed in a fast speed by the introduction of the V27ter / V29 automatic connection process allowing programmable alternations of the speech mode to the given mode, for example for an audiotex or audiovideotex service at 9600 bps.

3) Physical recovery during communication
The physical recovery process is implemented in particular during variations of the template of the line or during disturbances generating erroneous short sequences. I1 makes it possible to carry out a new matching of the equipment according to the same modulation allowing resynchronization of the modems at both ends according to the new characteristics of the line.

Due to the possibility of dial tone detection of the modem component during communication, it is possible to distinguish the unexpected presence of a carrier in the original transmission modulation.
V27ter or V29. This mechanism of resumption of transmission is possible by the presence of segments 1 and 2 of the long learning sequence indicating the beginning of the recovery process. The "speaking" mechanism is here also used as an indication signal of a physical recovery, during communication, for example at the initiative of the remote equipment.

The recovery mechanism can be based on the possibility for the receiving equipment, in case of reception of one or more erroneous synchronization short sequences (alternat), to perform a new physical matching. In fact, during communication, the desynchronism of the two modems (non-convergence of the equalizers) can be generated by variations of the template of the line or during disturbances on the telephone network. Contrary to the case of the passage in voice mode, and in data mode, this phase of connection is carried out only at the physical level without loss of connection of the higher levels namely the level field and the level packet, and without modifying the parameters of these levels higher. This is made possible, as will be described later, by the fact that the establishment time of a new communication at the physical level, that is to say the time required for the exchange of long learning sequences, remains short enough for the PLC, known per se, which manages the connection at the frame level and at the packet level, remains in a data waiting mode. In other words, for the automaton (frame / packet) everything happens, during a recovery phase, as if the other equipment was slow to send data.

 It should be emphasized that the exclusive use of short learning sequences (without segments 1 and 2) to obtain a useful bit rate appropriate to the applications envisaged is based on the assumption of a stationary transmission line (no training sequence). long permanently) and short distance ("Miniteî" - "PAVI">.

4) Falling V29 communication speed in
V27ter
Due to the possibility of tone detection during communication and more particularly during resumption of communication, it is possible to distinguish the presence of a carrier in the V29 transmission (V27ter). This fallback mechanism is possible by the presence and detection by the receiving equipment of segments 1 and 2 of the long learning sequence indicating the beginning of the fallback process and the modulation used.

The fallback mechanism is based on the possibility that the receiving equipment, in the event of receiving an erroneous long learning sequence, is present during the resumption process in modulation.
V29, to resynchronize at the physical level of modems in V27ter modulation. If the particularly difficult reception conditions do not make it possible to successfully resume communication V29, it is then possible to resynchronize the modems V27ter, given the better robustness of this modulation vis-a-vis the disturbances of line.

As in the case of physical recovery, the mechanisms of resumption of communication and retraction of speed do not disturb the higher levels (frame and packet), although there is change of modulation.

These last two processes (recovery and fallback) offer the possibility of maintaining communication, specifically and physically, even in difficult reception conditions due to disturbances affecting the quality of the transmission medium. They allow, in terms of application, to avoid prematurely breaking the transmission, which is very important, especially in the case of file transmission; this optimum self-adaptation of the V27ter / V29 transmission is likely to allow, whatever the physical medium, not only comfortable interactive communications, but also fast and reliable information transfers.

The invention will now be described in more detail with examples corresponding to the transmission modes V23, V27ter and V29.

Reference will be made, as prior art, to the following documents - CCITT Recommendation V25 (in particular last paragraph of Chapter 5, page 129), the connection procedure used in the "Minitel".

- CCITT Recommendation V27ter (in particular the long and short learning sequences defined in Table 3 on page 202), - CCITT Recommendation V29 (in particular the long learning sequence defined in Table 5 on page 221), - Annex F of the recommendation T104 of the CUIT? allowing to standardize the short learning sequence in V29 with segments 1 and 2, necessary for the fast speed function of "Minitel" at 9600 bps, - CCITT recommendation X32 (in particular LAPX frame synchronization and X25.3 packet, setting in particular on the equipment of the EBS network
TRANSPAC, - CCITT recommendation T71 (special features of LAPX), and TELETEL equiments Speed Fast (V27ter / V29) - recommendations T104 (pr ETS 300221) and T105 (pr ETS 300223) of the CCITT, - STUPAV (technical specifications videotex access point users) (version 1991) from FRANCE
TELECOM, - STUM (Technical Specifications of Users of "MINITEL" (versions 2VRP, MlB, M2, and M12) of FRANCE
TELECOM.

In order to improve the comfort and speed of consultation of "Teletel" services from "Minitel" type professional, it is planned to increase the transmission speed to 4800 Bits / s then to 4800/9600 Bits / s between Access Point "Teletel" and "Minitel".

V27ter modems (4800 bits / s), V29 (9600 bits / s) of facsimile type 3 are known (ROCKWELL R96 VFX).

The transmission rate is 9600 or 4800 Bits per second on both channels, with the modem running in alternate mode.

The actual rate of the link "PAVI1, -" Minitel "is optimized by the use of short training sequences at each reversal of the modems, the characteristics" short and stationary line "of this link allowing the use of this mode. The V27ter standard has both types of learning sequences (long and short) but the standard
V29 initially has only the long learning sequence. For this purpose, based on the R96VFX component, the Rockwell company developed, in collaboration with the Applicant, the V29 short learning sequence, which is integrated in Appendix F of the CCITT Recommendation T104.

The communication protocol between "PAVI" and "Minitel" fast speed, establishment, management and release, is in accordance with recommendations X25, X32 and T71 of CCITT, STUR TRANSPAC and recommendations T104 and T105 of the CCITT and the services of basis of the draft ETSI prETS 300 221 and
ETS 300 223.

Physical connection procedure (line level)
The physical connection process of the equipment according to the invention allows the automatic adaptation of the transmission speed to that of the called equipment, while presenting the same process as in connection
V23 and respecting the recommendations V25 and V100 of the
CCITT.

The main objective is to specify the physical connection processes of the "Minitel" V23 / V27ter, the "Minitel" V23 / V27ter / V29 and the "PAVI" V27ter and
V29 / V27ter, taking into account the following constraints - optimize the connection times with "Minitel" evolved in terms of Speed V23 / V27ter / V29, "Minitel" 2 VRP (Fast Photographic Speed)
V23 / V27ter and the "Minitel" 2 VR (Fast Speed) V23 / V27ter / V29, and / or - have a behavior compatible with the accesses "PAVI" V29 / V27ter with 9600/4800 bits / s vis-a-vis the terminals calling at 4800bps or 9600bps (backward compatibility), and / or - allow modem cards and boxes to be connected
V27ter currently existing (eg "EBS
Transpac "), and / or - automatically distinguish the connection of the" Minitel "on a" PAVI "V23 from that on a" PAVI "Fast Speed
V29 / V27ter without special action of the user.

The basic principles are related to the possibilities of V27ter / V29 modems currently on the market (eg the R96EFX / VFX) which, thanks to their internal signal processor, also reliably provide selective digital filtering functions.

The originality of the connection principle is therefore based on the preliminary analysis of the pure frequencies or tones present on the telephone link. Indeed, before any connection attempt, a detection of the tones makes it possible to discriminate the carrier frequencies of the modulations V27ter, V29 and the rest frequency of the modulation V23 (respectively 1800 Hz, 1700 Hz and 1300 Hz), even the telephone signaling ( 440 Hz clocked). The unmodulated frequencies in V27ter and V29 with a duration of 187.5 ms for the R96VFX correspond to the first segment of the long learning sequence. (cf recommendation
V27ter and V29 for the meaning of the segments of the short and long learning sequences).

Similarly, the originality of the principle of readaptation is based on the analysis during communication of the carrier frequencies of the modulations
V27ter, V29 allowing a resumption of the physical level (synchronization of the modems clocks) without disturbing the higher levels, either during variations of the line template or during disturbances, and more generally of any cause generating erroneous short training sequences , on the order of one of the equipments.

 It should be emphasized that the full recovery mechanism, leading to a change and in particular a modulation fallback (V29 -> V27ter), maintains the parameters of the higher levels (for example the packet level anticipation window), leading to a slight decrease of interactivity.

Based on this principle of detection of tones by digital filtering, this operation allows the "Minitel" V23 / V27ter / V29 to adapt, quickly and reliably, their transmission speed with respect to a remote device (V23, V27ter, V29) and with respect to the used line (template, disturbances, etc ...).

The characteristic tones detected by the modem in the connection phase are - 440 Hz to detect the telephone signaling, - 1300 Hz to enable the management of the V23 connection - 1700 Hz to detect the unmodulated carrier V29, - 1800 Hz to detect the non-carrier V27ter modulated, - 2100 Hz to handle the CCITT recommendation V25.

The characteristic tones detected in the communication phase for eventual physical recoveries are - 1700 Hz to detect the unmodulated carrier V29 (recovery in V29), - 1800 Hz to detect the unmodulated carrier V27ter (recovery in V27ter).

We distinguish two cases: the operating principle for the called equipment and that for the calling equipment. It is the modem of the called device which, following an incoming call, responds in a known manner by the 2100 Hz tone (see recommendation V25). In general, the access point "PAVI" is the called equipment, the "Minitel" is the calling equipment. However, the establishment of the physical connection can be obtained, as will be seen later, on one or the other equipment, depending on the case, after exchange without fault of long train tuning: the first equipment sends a long tuning train; if the second equipment receives it correctly, it in turn transmits a long tuning train; if the first equipment receives it correctly, communication is established at the physical level, which results in the first equipment transmitting a short synchronization train, followed by data, or signals to establish the frame-level communication , then back to the packet level, in a manner known per se.

The hardware architecture of the V27ter modem accesses of "PAVI" Fast Speed ("PAVI" VR) (usually called equipment) is based on the R96EFX
Rockwell. That of access V29 / V27ter "PAVI" VR second generation is based on possibilities at least equal to the R96VFX box (digital filtering capacity, short train V29 ...).

The access of the "PAVI" VR (fast speed) being only called to 9600/4800 bits / s, only the detections of the frequencies carrying modulations
V27ter (1800 Hz) and V29 (1700 Hz) are required at this level.

The synoptic of a MINITEL card Fast speed
V23 / V27ter / V29 according to the invention is given in FIG. 1B. It includes an INTEL 80C154-1 microcontroller MC connected via a BUS bus link to a 32 kbyte "NEC" 43256 SRAM memory associated with a backup battery
P, to a programmable read-only memory EPROM of the company "INTEL" 27C512 of 64 kbytes and to a modem MDM1 of the company "ROCKWELL" RD6VFX (V27ter / V29). The MC microcontroller is connected to an MDM2 "HERMES" V23 (ALCATEL) modem via a serial TTL-type LS link. The outputs of the MDM1 and MDM2 modems are applied to the inputs of a DX duplexer for connection to an LT telephone line. It will be understood that such a MINITEL card can operate in V27ter / V29 only by removing the modem MDM2.A card
Minitel operating only in V27ter can be realized using as modem MDM1, a modem
R96EFX.

Connection phase detection - In reception mode of the long learning sequence V29 or V27ter is associated a detection filter of 1700 Hz and 1800 Hz. The reception mode is activated after the emission of 3.3 seconds of 2100 Hz followed by a silence of 150 ms plus or minus 20 ms.

- On reception of segment 1 of the long learning sequence (identification for at least 100 ms of the unmodulated 1700 Hz frequency), the "PAVI" programs the modem in reception mode V29 for reception of the long learning sequence complete (packaging segment). The "PAVI" then transmits for sending the corresponding long learning sequence (segments 1 to 5).

The physical connection is established in V29 modulation.

- On reception of segment 1 of the long learning sequence (detection of at least 100 ms of the frequency 1800 Hz unmodulated), the "PAVI" programs the modem in reception mode V27ter for the reception of the training sequence long full. The "PAVI" then transmits for sending the corresponding long learning sequence. The physical connection is established in V27ter modulation.

Two cases are to be considered depending on whether the equipment includes a V29 / V27ter modem or only V27ter.

a) Case of a V29 / V27ter modem (such as R96VFX) - Without known frequency reception, after a delay of 2 seconds after the end of the 2100Hz tone emission, the "PAVI" V29 / V27ter by default performs the processing following sending of a long learning sequence V29, without response from the remote equipment after 2 seconds, renewal of the sending of a long learning sequence V29, without response from the remote device after 2 seconds, last connection attempt in V29 mode by a new sending of a long learning sequence V29, no response from the remote device, connection attempt in V27ter mode by sending a long learning sequence V27ter, no response from the remote device after 2 seconds, sending a short learning sequence
V27ter, then complete renewal of the mechanism described in the two previous paragraphs (long train + short train) until the expiry of the connection waiting time delay (generally 40 seconds) or on the response of the remote equipment.

b) Case of a V27ter modem (such as R96EFX) - Without known frequency reception, after a delay of 2 seconds after the end of the 2100Hz tone emission, the "PAVI" only V27ter performs the processing next - sending a long learning sequence V27ter, - no response from the remote device after 2 seconds, sending a short learning sequence
V27ter,. then complete renewal of the mechanism described in the two previous paragraphs (long train + short train) until the expiry of the disconnection timer or on the response of the remote equipment.

Principle of detection in the communication phase (recovery process)
Two processes are to be considered, depending on the influence of on-line disturbances and "real-time" variations of the transmission line template. * Recovery mechanism in the original modulation.
V29 (case ne11) or V27ter (case nid10), * V27ter modulation fallback mechanism with V29 origin modulation (cases 12 and 12a).

The hardware architecture of "Minitel 2" Speed
Fast Photographic (M2 VRP) and "Minitel" 2 fast speed VR (in general calling equipment) is based on Rockwell's R96 VFX modem box and on the Hermes case or its equivalent case
ST7514 from SGS-Thomson. In fact, these "Minitel" can connect indifferently to doors "Teletel" V23 and V27ter. Only 2100Hz, 1300Hz, and 1800 tones
Hz are then detected during the connection phase. In addition, the 1800 Hz tone is detected in the communication phase to ensure an erroneous short-circuit readaptation process.

It is possible to discriminate between modes V23 and
V27ter only with the first discriminant (nominal duration of the silence of 75 or 150 ms), and thus not to detect the frequency 1800 Hz. The reception of a long learning sequence V27ter is done on the segments 3 to 5 only , the modem having been set in this mode after detecting a silence of 150 ms.

The Minitel Speed V23 / V27ter / V29 must be able to connect indifferently to doors "Teletel" V23, V27ter and V29 / V27ter. As a result, the 2100 Hz, 1300 Hz, 1700 Hz and 1800 Hz tones are detected during the connection phase. In addition, the 1700 Hz and 1800 Hz tones are detected in the communication phase to ensure the physical recovery-adaptation process. The 440 Hz tone can be searched continuously to monitor the telephone signaling.

By pressing the connection / end key, the "Minitel" is connected to a line connection and is able to detect the frequencies 2100 Hz, 1800 Hz, 1700 Hz and 1300 Hz, the frequency 440 Hz is sought if energy is present on the line, without presence of the preceding frequencies. These frequencies are validated if the duration of the signal is at least equal to 300 ms for the 2100 HZ, 80 ms for the 1300 Hz, 100 ms for the 1700 Hz and 100 ms for the 1800 Hz.

The "Minitel" 2 Fast Photographic Speed switches to V23 modulation if - 300 ms of 2100 Hz are detected followed by 75 ms (+ or - 20 ms) of silence then of 80 ms of 1300 Hz, - the frequency of 2100 Hz n ' is not detected, but the frequency of 1300 Hz is detected for 1.7 s (or 1.8 s from the M2).

This behavior meets the requirements of the STUM recommendations for the entire management and connection part in V23 modulation.

The "Minitel" Fast Photographic Speed switches to V29 modulation and emits its long learning sequence if - at the reception of the frequency 2100 Hz, the silence which follows is 150 ms (+/- 20 ms) knowing that the modulation the the fastest of the "Minitel" is the V29, - segment 1 of the long learning sequence (187.5 ms of 1700 Hz validated for 100 ms) is detected by the digital filter; the "Minitel" programs the modem in reception mode V29 to receive the complete long learning sequence. The physical connection is established by programming the modem V29 modulation in the mode of short training sequences, after the transmission of the long learning sequence V29, - detection of three short sequences V29 consecutively erroneous (recovery process).

The "Minitel" evolved in terms of Fast Speed switches to V27ter mode and emits a long learning sequence if - on receiving the frequency 2100 Hz, the following silence is 150 ms (+/- 20 ms) knowing that the fastest modulation of the "Minitel" is the V27ter, - the segment 1 of the long learning sequence (187.5 ms of 1800 Hz validated during 100 ms) is detected by the digital filter, the "Minitel" program the modem in V27ter receive mode for receiving the complete long learning sequence. The physical connection is established by programming the modem V27ter modulation in the mode of short training sequences, after the transmission of the long learning sequence V27ter.

- On receiving the frequency 2100 Hz, the following silence is 150 ms (+/- 20 ms) knowing that the fastest modulation of the "Minitel" is the V29. The "Minitel" then transmits the long learning sequence
V29. If, at the expiry of a delay of 10 seconds, the correspondent (generally a "PAVI" access point) has not transmitted a known frequency, the "Minitel" programs the modem in reception mode V27ter in order to detect the presence of an incomplete V27ter learning sequence (absence of segments 1 and 2, as is the case for EBS). For this purpose, it suffices to suppress the logical detection condition of the segments 1 and 2 in the sequencing. The validation of the reception of a long compliant train is then carried out in a conventional manner on the segments 3 to 5. At the recognition of the V27ter long train incomplete, the "Minitel" transmits in response the complete long learning sequence V27ter (there is no problem in transmitting the segments 1 and 2) and the communication is established in V27ter modulation, in the short training mode, - at the reception of the 2100 Hz frequency, the following silence is 150 ms (+/- 20 ms) and the fastest modulation of the "Minitel" is the V29, the Minitel transmits then the long learning sequence V29. If the "Minitel" detects the presence of the unmodulated frequency (or segment 1) of the V27ter (187.5 ms of 1700 Hz validated for 100 ms), then it programs the modem for the reception of the long learning sequence
V27ter. In response to the long learning sequence
V27ter complete, the "Minitel" emits the complete V27ter long learning sequence. Communication is established in V27ter modulation, in the mode of short learning sequences.

consecutive detection of, for example, three errored V27ter short sequences or for example three erroneous V29 short sequences followed by one or two erroneous long V29 sequences (recovery process).

According to the invention, a long learning sequence (segments 3 to 5) is preceded by the transmission of, for example, 180 to 200 ms of unmodulated carrier (segment 1) followed by 20 ms of silence (segment 2). The transmission of the long learning sequence is conditioned for the calling equipment
For V29 modulation - either by recognition of the 2100 Hz frequency for 300 ms followed by a silence greater than 150 ms, - by the recognition of the 1700 Hz frequency for 100 ms followed by the recognition of the training sequence long V29 issued by the modem of the called equipment, - either by the recognition of the frequency 1800 Hz for 100 ms followed by the recognition or not of the training sequence V27ter emitted by the modem of the called equipment, - either by the consecutive detection of three erroneous V29 short training sequences (recovery process).

For V27ter modulation - either by recognition of the 1800 Hz frequency for 100 ms followed by the recognition of the V27ter long learning sequence transmitted by the modem of the called equipment, - or by the recognition of the 1700 Hz frequency during 100 ms followed by the non-recognition of the long learning sequence V29, modulation not managed by the calling equipment, or by the only recognition of the long learning sequence V27ter received without the presence of the segments 1 and 2 (case of EBS), - either by the consecutive detection of three erroneous V27ter short training sequences (recovery process), - or by the consecutive detection of three erroneous V29 short training sequences followed by a training sequence long erroneous V29 (recovery process).

For called equipment, the transmission of a long learning sequence (matching) is also always preceded by the transmission of 180 to 200 ms of unmodulated carrier (segment 1) followed by 20 ms of silence ( segment 2). The transmission of the long learning sequence is conditioned
For V29 modulation - either by 100 ms recognition of 1700 carrier
Hz followed by the detection of the long learning sequence V29, - either by the expiry of the delay of 2 seconds of waiting of tone, - or by the consecutive detection of three erroneous V29 short learning sequences (process of reprise).

for V27ter modulation - either by the recognition of 100 ms of carrier 1800
Hz followed by the detection of the long learning sequence V27ter, - either by the expiry of the delay of 2 seconds of waiting of tone, - or by the recognition of a long sequence
Learning V27ter without presence of segments 1 and 2 (case of EBS), - either by the consecutive detection of three erroneous V27ter short learning sequences (recovery process), - or by the consecutive detection of at least one, and for example three short learning sequences
V29 erroneous followed by one or two erroneous long V29 learning sequences (recovery process).

In order to pass into a short learning sequence (synchronization), which characterizes the connection at the physical level, the following two conditions must be met - having recognized the long learning sequence transmitted by the remote modem, - having issued its own sequence of long learning.

The modems of the two devices are synchronized and the exchanges then take place in the mode of the short training sequences.

During communication, if the modems are out of synchronization, the connection recovery process provides a return to the long learning sequences either in the same modulation or V27ter in case of desynchronization and failure of recovery in the V29 modulation (process fallback).

Diagrams of different types of connection
We have identified 6 configurations (cf case N "3 to 9) of fast speed connection given the diversity of equipment" Minitel "V23, V23 / V27ter,
V23 / V27ter / V29 and "PAVI" V23, V27ter, V29 / V27ter. In addition, we studied the configuration (cf Figure N "14) of connection of" Minitel "on the inputs
Synchronized Tunables of TRANSPAC (EBS).

Each case is the subject of a diagram to visualize the sequence of the physical connection process and to evaluate the connection time.

An early connection is defined as any semiautomatic or manual connection where the calling device recognizes 300 ms of 2100 Hz. The connection order (for example pressing the end-connection key or sending a sequence according to the protocol " Minitel ") arrives before the last 300 milliseconds of the 2100 Hz tone to the line management software.

Delayed connection is any connection (a priori manual) where the calling device can not recognize 300 ms of 2100 Hz. The connection order reaches the line management software in the last 300 milliseconds of tone 2100 Hz or later.

We call equipment V23 / V27ter or equipment V23 / V27ter / V29 any material called a "PAVI"
VR is a "Minitel" used in so-called "front" mode (micro-pavi), or any device that can be called and can meet the specifications of this document. We can specify that the behavior of the calling equipment can be applied to the terminal "Minitel" as well as to the "PAVI".

Segments 1-5 of a learning sequence
V27ter or V29 are as follows (according to recommendations
CCITT)
Segment 1: unmodulated carrier
Segment 2: No energy transmitted
Segment 3: Continuous Phase Inversions of 180
Segment 4: Equalizer conditioning sequence: 2 phases 0 and 180
Segment 5: Continuous emission of scrambled "1".

SI = unit interval of the dibit; the durations of the segments 3 to 5 are expressed in unitary intervals.
On the diagrams, the abbreviations represent respectively
TL: long learning sequence or long train (establishing agreement)
TC: short learning sequence or short train (synchronization)
TLV27: V27ter Long Learning Sequence or V27ter Long Train
TLV29: long learning sequence V29 or long train V29
TCV27: V27ter short training sequence or V27ter short train
TCV29: V29 short training sequence or V29 short train
TLV27: segment 1: 185 to 200 ms of unmodulated carrier; segment 2: 20 to 25 ms without transmitted energy; segment 3: 50 SI (unit intervals) segment 4: 1074 SI; Segment 5: 8SI
TC V27: no segments 1 and 2; segment 3: 14 SI segment 4: 58 SI; segment 5: 8 SI
TL V29: segment 1: 185 to 200 ms; segment 2: 20 ms segment 3: 128 SI; Segment 4: 384 SI; segment 5 48 SI
TC V29: no segments 1 and 2; segment 3: 100 SI segment 4: 62 SI; segment 5: 18 SI.

The nominal duration of the learning sequences is - TL V27 = 915 ms (including segments 1 and 2), - TL V29 = 441 ms (including segments 1 and 2), - TC V27 = 50 ms (without segments 1 and 2), - TC V29 = 75 ms (without segments 1 and 2).

The physical connection is established after the exchange between the two ends, long learning sequences, when passing in short learning sequences to establish the connections of the frame levels
LAPX and X25.3 package.

The table summarizing the types of physical connection and recovery (cases 1 to 14) is given below
Summary of physical connection types and recovery

0,9 s
Cas N 2 - connexion retardée à 1200/75 bps d'un équipement ("Minitel") V23/V27ter/V29 sur un équipement
V23

2,1 s nota :A partir du "Minitel" 2, le temps de connexion est de 1,8 s.<tb><SEP> Caller <SEP> called <SEP> mode <SEP> case <SEP> N
<tb><SEP> V23 <SEP> V23 <SEP> Anticipated
<tb><SEP> V23 <SEP> V23 <SEP> Delayed <SEP> 2
<tb><SEP> V23 <SEP> 1
<tb><SEP> V27ter / V23 <SEP> V27ter <SEP> Anticipated <SEP> 3
<tb><SEP> V29 / V27ter <SEP> 3
<tb><SEP> V23 <SEP> 2
<tb><SEP> V27ter / V23 <SEP> V27ter <SEP> Delayed <SEP> 4
<tb><SEP> V29 / V27ter
<tb><SEP> V23
<tb><SEP> V29 / V27ter / V23 <SEP> V27ter <SEP> Anticipated <SEP> 6
<tb><SEP> V29 / V27ter <SEP> 7
<tb><SEP> V23 <SEP> 2
<tb><SEP> V29 / V27ter / V23 <SEP> V27ter <SEP> Delayed <SEP> 4 @@
<tb><SEP> V29 / V27ter <SEP> 8.9
<tb><SEP> V27ter / V23 <SEP> V27ter <SEP> Recovery <SEP> 10
<tb><SEP> V27ter <SEP> 10
<tb><SEP> V29 / V27ter / V23 <SEP> Recovery
<tb> V29 / V27ter <SEP> 11
<tb><SEP> V29 / V27ter / V23 <SEP> V29 / V27ter <SEP> recovery <SEP> with
<tb><SEP> change <SEP> of <SEP> mode
<tb><SEP> V29 / V27ter / V23 <SEP> V29 / V27ter <SEP> Failed <SEP> 13 <SEP>
<tb><SEP> V29 / V27ter / V23
<tb><SEP> EBS <SEP> Transpac <SEP> Early <SEP> 14
<tb><SEP> V27ter / <SEP> V23 <SEP>
<tb> The estimates of the connection times as a function of the connection modulations, the calling devices (for example "Minitel") and the called devices are as follows (see summary table V23 modulation connection (including the transmission of the connection sequence 13, 53)
Case N "1 - early connection to 1200/75 bps of equipment (" Minitel ") V23 / V27ter / V29 on equipment
V23

0.9 s
Case N 2 - delayed connection at 1200/75 bps of equipment ("Minitel") V23 / V27ter / V29 on equipment
V23

2.1 s note: From "Minitel" 2, the connection time is 1.8 s.

Attempting to connect a V23 device to a V27ter or V27ter / V29 device is meaningless and will always lead to a connection failure. It is the same for a V27ter or V27ter / V29 equipment calling equipment only V23.

In these cases, the phone line automatically disconnects after a given timeout (40 sec).

1,38 s
Cas N 8 - connexion retardée à 9600 bps d'un équipement ("Minitel") V23/V27ter/V29 sur un équipement V27ter/V29

0,9 à 3 s connexion en modulation V27ter
Cas N"3 - connexion anticipée à 4800 bps d'un équipement ("Minitel") V23/V27ter sur un équipement
V27ter ou V27ter/V29

2,4 s
Cas N"4 - connexion retardée à 4800 bps d'un équipement ("Minitel") V23/V27ter ou V23/V27ter/V29 sur un équipement V27ter

1,9 à 3,9s
Cas N"5 - connexion retardée à 4800 bps d'un équipement ("Minitel") V23/V27ter sur un équipement V27ter/V29

1,9 à 9s
Cas N"6 - connexion anticipée à 4800 bps d'un équipement ("Minitel") V23/V27ter/V29 sur un équipement
V27ter

2,9s
Cas N"14 - connexion à 4800 bps d'un équipement ("Minitel") V23/V27ter/V29 ou V23/V27ter sur E.B.S.
TRANSPAC

15s.V29 modulation connection
Case N "7 - Early connection to 9600 bps of equipment (" Minitel ") V23 / V27ter / V29 on equipment
V27ter / V29

1.38 s
Case N 8 - delayed connection to 9600 bps of equipment ("Minitel") V23 / V27ter / V29 on V27ter / V29 equipment

0.9 to 3 s V27ter modulation connection
Case N "3 - Early connection to 4800 bps of equipment (" Minitel ") V23 / V27ter on equipment
V27ter or V27ter / V29

2.4s
Case N "4 - delayed connection to 4800 bps of equipment (" Minitel ") V23 / V27ter or V23 / V27ter / V29 on V27ter equipment

1.9 to 3.9s
Case N "5 - delayed connection to 4800 bps of equipment (" Minitel ") V23 / V27ter on V27ter / V29 equipment

1.9 to 9s
Case N "6 - early connection to 4800 bps of equipment (" Minitel ") V23 / V27ter / V29 on equipment
V27ter

2,9s
Case N "14 - connection to 4800 bps of equipment (" Minitel ") V23 / V27ter / V29 or V23 / V27ter on EBS
Transpac

15s.

In the case No. 1 (FIG. 2) after a line seizure following a DLT request to which the called equipment responds with 3.3 s of 2100 Hz, the connection command issued by the calling equipment "MINITEL" operating only in V23 mode, or in
V23 and V27ter, or even in V23, V27ter and
V29, is followed by detection by the latter whose modem is in receive mode of at least 300 ms of the 2100 Hz frequency transmitted for 3.3 s by the called V23 equipment ("PAVI"). Detection according to the invention of 75 ms of silence after the emission at 2100
Hz is used to validate the known connection procedure according to the V23 mode (detection by the calling device of at least 80 ms of a signal at 1300 Hz transmitted for 40 seconds by the "PAVI-V23", and transmission by calling equipment with a frequency of 390 Hz, and establishment of the full duplex connection ("fullduplex").

Case No. 2 (Figure 3) corresponds to a delayed connection The connection order occurs after the end of the 2100 Hz emission (or too late for the calling equipment to detect 300 ms of the 2100 Hz frequency In this case, the calling equipment identifies a device V23 called, by detection (known per se) of 1.8 seconds signals at 1300 Hz.

Case No. 3 (FIG. 4) corresponds to the early connection of a V23 / V27ter "MINITEL" to equipment responding in V27ter mode After detection of 300 ms at the 2100 Hz frequency, the calling equipment detects a silence of 150 ms, indicating that the communication will not be in V23 mode The calling equipment sends a long TL V27 train (including segments 1 and 2) and the called equipment detects the frequency of the carrier (1800 Hz) which characterizes the mode V27ter (detection of 100 ms of 1800 Hz of the segment 1) The equipment called (for example PAVI V27ter or V27ter / V29) positions (if necessary) its modem in mode V27ter and then emits a long train TL V27 (including segments 1 and 2) which is received by the calling equipment. If this reception is valid, the connection is established (each device has transmitted and received a long TL V27 train) and the communication is established by exchange of TC short trains
V27 in V27ter mode (without segments 1 and 2). During the exchange of TC V27 short trains, the connection is established first at the frame level (LAPX), then at the packet level (X25) in a manner known per se.

Case No. 4 (FIG. 5a) corresponds to a delayed connection to a V27ter equipment.In a line-seizing order and without transmission of the calling equipment, the called equipment transmits, after a time interval of 200 ms after the end of the 2100 Hz (3.3s) emission, an alternation of TL V27 long trains and TC V27 short trains at a rate of 2 seconds (until a delay of 40 seconds has elapsed after which, in the absence of a successful connection, the called equipment automatically releases the link).

After the connection order, the calling equipment in reception mode, detects 100 ms of the frequency 1800 Hz of the first long train TL V27 it receives and following this reception, it sends in turn a long train TL 27 which is received by the called equipment. The connection is established at the physical level, each of the equipment having emitted and received a long train V27.

The communication continues in V27ter mode by exchanging TC V27 short trains and establishing the synchronization of the higher levels (frame and packet).

Case No. 4bs (FIG. 5b) differs from the previous one in that the calling Minitel operates at least according to the modes
V27ter / V29 while called equipment does not operate in V29 mode. The calling equipment detects the characteristic 1800 Hz frequency of the V27ter mode, but in response, it sends this time a V29 long train to make a V29 connection attempt.

Called equipment not recognizing the long train
V29, transmits again a long train V27ter, to which the calling equipment responds by a long train V27ter, which allows the establishment of the connection. This procedure makes it possible to check whether the called equipment is likely to connect in V29 mode (see further case ne9).

Case No. 5 (FIG. 6) corresponds to a delayed connection to a V29 / V27ter device After the silence of 200 ms following the emission at 2100 Hz, the called equipment tries to establish the communication in V29 mode.

The calling equipment V27ter / V23 remains "mute" because its modem, in reception mode after the connection order, does not recognize the carrier frequency V29 (1700 Hz) in segment 1 of the TLV29 trains. After three unsuccessful attempts in V29 mode (6 seconds in total), the called equipment transmits a long TL V27 train whose unshielded 1800 Hz carrier of segment 1 is detected by the modem of the calling equipment which in turn transmits a TL V27 long train whose unmodulated carrier at 1800 Hz is detected by the modem of the called equipment. The connection is then established at the physical level, and continues by exchanging TC V27 short trains and establishing higher levels (frame and packet).

According to the nabis case (FIG. 6b), the calling equipment is capable of recognizing the frequency of 1700 Hz, although it does not operate in the V29 mode, (it suffices to add an additional filter to the modem), and it transmits directly a V27ter long train, hence a much faster connection than in case 5, by exchange of two V27ter long trains.

Case No. 6 (Figure 7) concerns the early connection of a calling device V29 / V27ter or V29 / V27ter / V23 to a device called V27ter, after detection of 150 ms of silence after detecting 300 ms of 2100 Hz. The calling equipment sets its modem in transmission mode V29 and transmits a long train TL V 29. The called equipment does not recognize a long train TL29, it in turn transmits, after a delay of 2 seconds, a long train TL V27. calling equipment detects 100 ms of the frequency 1800 Hz of segment 1 of long train TL
V27 and position its modem in V27ter mode. The duration of segments 1 and 2 allows this operation to be performed before the arrival of segment 3. The calling equipment therefore recognizes the long train TL V27 and in turn responds to a long train TL V27. Communication is established at the physical level. , and continues as before (exchange of short trains ...).

Case No. 7 (FIG. 8) is similar to case No. 3, except that the communication is established in mode V29 in which the two devices can operate.

Case # 8 (Figure 9a) is similar to Case # 4 except that communication is established in V29 mode.

Case No. 9 (FIG. 9b) is close to the Nabis and No. 8 cases, but the delayed connection order occurs while the called equipment transmits long trains in the V27ter fallback mode, after three transmission attempts. long trains V29. In this case, the calling equipment sends a long train V29 which allows the establishment of communication in V29 mode.

Case No. 10 (FIG. 10) concerns a process of resumption of transmission in V27ter mode (without change of mode) After reception of three non-compliant TC27 short trains, a piece of equipment (here the calling equipment) resumes the process of learning in V27ter modulation by emitting a TL V27 long train.

The called equipment, whose modem in receive mode continuously searches for the unmodulated carrier frequency, detects the frequency 1800 Hz in segment 1 of the long train TL V27, which enables it to identify the recovery process (the trains short do not have segments 1 and 2). I1 receives the long train
TL V27 and in turn transmits a long TL V27 train that is received by the calling equipment. The recovery process has been completed and the communication continues by exchanging TC V27 short trains. This process does not disrupt the higher levels (trains and packets) because no disconnect signal is issued. The recovery process has a duration less than an automatic disconnection delay of the higher levels for which everything happens as if there was a delay in sending the information.

Case No. 11 (FIG. 11) is similar to case ne10, except that the resumption is carried out in mode V29 (without change of mode) with detection of the unmodulated 1700 Hz frequency (segments 1 and 2 of TL V29) by the equipment called.

Case No. 12 (Figure 12a) describes a recovery process with mode change after receiving three non-compliant TC V29 short trains (eg line disturbance), equipment (here calling equipment) resumes the process. V29 modulation by transmission of a long train TL V29 This attempt being unsuccessful (here only one attempt), the calling equipment transmits a long train TL V27 whose carrier frequency of the segment 1 is detected by the This device positions its modem in V27ter mode before receiving segments 3 to 5 of the TL V27 long train, and in turn transmits a long TL V27 train which is received by the called equipment. short TC V27 without disturbance of the higher levels (frame and packet) due to their compatibility to a few parameters.

Case No. 12bis (FIG. 12b) corresponds to the previous case, but the learning process is repeated twice in V29 mode (two attempts) and twice in V27ter mode (two attempts).

Case No. 13 (Figure 13) relates to an aborted recovery from a V29 mode communication A device (eg calling equipment) receives three non-conforming TC V29 short trains. V27ter mode (as in the full case) After receiving two non-compliant TL V27 long trains (two attempts), the calling equipment interrupts the call.The number of two attempts is given as an example, but it can be considered to make a single attempt.

Case No. 14 (Figure 14) relates to the connection to a synchronous standardized input (EBS) of the current network
TRANSPAC, in V27ter mode. The process starts as in case No. 7. The long train TL V29 (or possibly TL V27) is not recognized by the receiver EBS, which transmits a long train (TL 27 fallback) corresponding to a fallback mode at 2400. bps then short trains (TC V27 fallback) corresponding to the fallback mode.The calling equipment receiving no known mode for a delay time of 10 seconds (failure to detect the unmodulated carrier), it automatically programs its modem in reception of long trains TL V27 without segments 1 and 2, that is to say that it suppresses the logical condition of detection of the frequency of the unmodulated carrier. The duration of 10 seconds is sufficient to discriminate this case with respect to others (especially case 5).

Case No. 15 (FIG. 15) relates to the known procedure for switching to the voice-data mode with the V23 modulation.

The called equipment issues a tilt sequence in speech mode for N seconds. A disconnection is performed by dropping the carrier without breaking the telephone link and an audible message is transmitted for a selected delay time. When the timer expires, the complete connection is again performed in a conventional manner (equipment
MINITEL V23).

Case No. 16 (Figure 16) relates to a phonedonne process according to the invention in V29 modulation.The voice switching sequence produces a logical disconnection with release of the higher levels (packet and frame) and physical disconnection by falling of the carrier. An acoustic message is emitted during a given delay interval (telephony mode) When the timer expires, the connection is resumed in V29 mode at the initiative of the called equipment (TL V29 transmission) and the physical connection is established. after an exchange of TL V29 long trains, then at the packet and frame level in the following TC V29 short trains for a restoration of the previous V29 modulated state.

Case No. 17 (FIG. 17) is analogous to the procedure except that the given mode is the V27ter mode folded back from the V29 mode.After the reconnection in the given mode, the called equipment attempts a recovery in V29 mode. this attempt, recovery is performed in V27ter fallback mode significantly less sensitive to disturbances of the line.

Case No. 18 (FIG. 18) is analogous to case ne17, but recovery in V29 mode is successful and the connection is made physically in long trains TL
V29, then at the frame level and at the packet level in the following TC V29 short trains.

Case No. 19 (FIG. 19) also relates to a voice-data process, in which the calling equipment makes an anticipated request to return to communication in data exchange mode, before the end of the time-out period of N seconds of the mode. This anticipated demand is manifested in the form of the transmission of an unmodulated carrier segment 1 V29, to which the called equipment responds by an attempt to connect in V29 mode (transmission of long trains V29). In this case, the connection can not be established in V29 mode, the called equipment then transmits V27ter long trains (fallback mode) leading to a synchronization in V27ter mode, it will be noted that the anticipated demand for return in exchange mode. of data by a V27ter-only device is effected by the transmission of an unmodulated carrier segment 1 V27ter.

Case 20 (FIG. 20) is analogous to case 19, except that the return to data exchange mode is successful in mode V29.

Figs. 21a to 21s provide the write instructions for the basic operations implemented in the sequencer, from the ROCKWELL R96-VFX modem instruction set, for V27ter or V29 operation. These instructions are implemented in the next higher level sequences of FIGS. 22a to 22d, for the emission of the long and short trains in V27ter and V29, and for the reception of these trains in FIGS. 23a to 23d, for which it will be noted in particular the characteristic signals VRECTL V29 and VRECTC V29,
VRECTTL V27 and VRECTTC V27 characterizing the correct reception (= OK) respectively of a long train V29, a short train V29, a long train V27ter and a short train V27ter.

FIGS. 24 to 24d further characterize the end of transmission phases of such trains and FIGS. 25a to 25f, the end of reception of such trains, FIG. 25c to f concerning the case of long or short trains presenting application data. (flag or "flags" and data).

The automaton of FIG. 26a comprises a sequence of operation in local mode, making it possible to switch following an order of connection OC sent or received, either to a connection automaton in calling mode AC1, or to a connection automaton in called mode AC2, which are also connected to an ACV23 communication controller in V23 mode. Each of the automata
AC1 and AC2 is connected to an ACV27ter controller in
V27ter and / or a PLC in V29 ACV29 mode.

The PLC ACV29 is connected to a recovery machine in V29 ARV29 mode, to allow one or more retry-adaptation attempts in V29 mode which can also be connected to a fallback PLC
AREP allowing a fallback to the ACV27 PLC.

The ACV27 controller may also be equipped with an ARV27 V27 recovery controller to allow one or more replay-adaptation attempts in the same mode.
V27ter. The ACV27 and ACV29 controllers are also connected to an APH PLC allowing a passage in voice mode, which in turn is connected to an APHD PLC for voice-data switching for a return to a positioning either in V29 mode (PLC ACV29) or in V27ter mode (PLC ACV27).

In addition, the line can be released (return to "local" mode) from the controllers ACV29, ACV27, ARV27 and
APHD.

According to FIG. 26b, the PLC in calling mode (left column) after the connection command that it sends following a telephone line seizure at its initiative, with a delay (90 s) and programs the simultaneous detection by the multi-frequency modem (1300 Hz, 1700 Hz, 1800 Hz, 2100 Hz) (Figure 27b). The PLC in called mode allows, after a received connection command, with a connection delay (40 s) and emits a response tone (2100 Hz) (see point 1, figure 28a).

With regard to the connecting machine in the calling mode (FIGS. 27a to 27g), a general diagram is given in FIG. 27a. The left branch represents a connection in V27ter mode (detection of 1800 Hz) and the right branch in V29 mode (detection of 1700
Hz). Figure 27b shows the branch performing the detection of the characteristic frequencies of each modulation. If detection of 300 ms of 2100 Hz (so-called anticipated connection), passage to point B (Figure 27c), then in the absence of 1300 Hz which would characterize a V23 mode, passage from point F (Figure 27d) to transmit a long train V29. If detection of 1700 Hz, transition to point D (Figure 27f) for establishment of the communication in V29 mode. If detection of 1800 Hz, passage to point C (Figure 27e), and emission of a long train V27ter (because no previous transmission of long train V27ter) and communication in V27ter (signal
COM V27-1 - see fig. 30c and 30d). Figure 27c shows the sequencing from point B of Figure 27b (300 ms detection of 2100 Hz) and leading to either a connection attempt at V23 (20 ms at 1300 Hz) or at point F (Fig. 27d) . From point F (fig 27d), and after detection of 150 ms of silence, connection attempt in V29 and connection in V29 mode (point D and fig 27f) or in V27ter mode (point
G and fig 27e).

In Fig. 27e, in case of erroneous reception of a long train V27ter, new connection attempts (point G of Fig. 27d) and release of the link at the expiry of the delay of 15 s. In FIG. 27f, in case of erroneous reception of a long train V29, a new connection attempt (point G of FIG. 27d) in
V29 and / or V27ter until expiry of the time delay. In Figure 27e, after successful reception of a long train V27ter, and in the absence of long train previously emitted and 2100 Hz previously detected, transmission of a long train V29 (Figure 27g, point H) in order to a so-called delayed connection in V29 according to case No. 9.

To obtain a single-mode automaton, it suffices in FIGS. 27a to 27g to delete the sequences corresponding to the unused mode (emission of the long and short trains, detection of the unmodulated carrier frequency).

The called-mode connection automaton, whose general diagram is given in FIG. 28a, comprises the sequences making it possible to discriminate between the modes
V23, V27ter and V29, a V29 mode handshaking sequence being shown in Figure 28c, in V27ter mode in Figure 28d, and in V23 mode in Figure 28e. As before, the operation in two modes or in a single mode (V27ter or V29) can be obtained by removing from the sequencer the superfluous elementary sequences.

In FIG. 28b, the NB PASSAGE parameter makes it possible to make several attempts (3) to connect in V29 mode and / or in V27ter mode by transmitting a long train without valid reception of a long train back (point 6 of the fig 28b, 28c and 28d).

The voice-data switching sequencer is represented in FIGS. 29a to 29c, and allows a new setting in communication in V29 mode through sequences of FIG. 28c and in V27ter mode through the sequences of FIG. 28d, however, this does not imply that the equipment includes the entire called-mode connection controller. The same goes for the procedure for releasing the link in FIG. 29b (point 6 of FIG. 29a).

The V29 modulating communication and resumption-adaptation automaton (FIGS. 30a to 30b) makes it possible to perform a resumption-adaptation in the same mode, or else in the V27ter fallback mode. The recovery-adaptation automaton also ensures short train transmissions after communication (COM V27-1, COM V27-2,
COM V29-1 and COM V29-2). The NB PASSAGE parameter makes it possible to carry out several attempts (here 2) of readaptation in V29 (FIG. 30b) and / or V27TER (FIG. 30d).

The two automata (vertical branches of FIGS. 30a and 30c) ensure the sending of short trains V29 and V27ter and activate the short-circuit resumption-adaptation sequences (VRECTCV29 = OK or VRECTCV27 = OK).

Claims (15)

 1. Resumption-adaptation method for at least one duplex modulation between two equipment A and B through a telephone line, characterized in that it uses, during the exchange of signal trains of synchronization possibly followed by application information, an exchange of signal streams of agreement on the initiative of a device called first equipment for recovery-adaptation, each train of agreement signals starting with a non-carrier signal modulated of given nominal duration having a carrier frequency characteristic of the transmission mode, the other equipment being called second equipment for resumption-adaptation, in that each of the two equipment A and B is arranged to detect the frequency of said signal unmodulated carrier and in that the equipment A and B are arranged to perform the exchange of two sets of tuning signals according to the following apes  a) initialization by the first equipment of a revision-adaptation.  b) transmission by the first equipment of a tuning signal stream in a duplex duplex transmission mode for synchronization signal train exchanges.  c) analyzing by the second equipment the frequency of the unmodulated carrier signal of said tuning signal stream.  d) in the event of recognition of this frequency characterizing a request for adaptation resumption, positioning of the second equipment in reception of a train of tuning signals.  e) in case of validation by the second equipment of the reception of said tuning signal train, adaptation of the second equipment according to said transmission mode.  f) transmission by the second equipment of a train of tuning signals according to said recognized transmission mode.  g) analyzing by the first equipment the frequency of the unmodulated carrier signal stream of said tuning signal stream.  h) in case of recognition of this frequency, maintaining the positioning of the first equipment in reception in said transmission mode.  i) in case of validation by the first equipment of the reception of the train of tuning signals emitted by the second equipment, adaptation of the first equipment according to said transmission mode.  j) resuming the exchanges of synchronization signal trains, possibly followed by application information without breaking the higher logical levels of the communication protocol of the two devices.  2. Method according to claim 1, characterized in that the equipment A and B are arranged to manage at least a second half-duplex transmission mode slower than said transmission mode, but more robust vis-à-vis -vis disturbances online and in that the equipment A and B are arranged to perform the following steps after steps a) to g)  k) in case of non-recognition by the first equipment of the train of tuning signals transmitted by the second equipment, transmission by the first equipment of a train of matching signals in the second transmission mode  1) Analysis by the second equipment of the frequency of the unmodulated carrier signal of said train of tuning signals transmitted by the first equipment  m) in case of recognition of said frequency during step 1), which then characterizes a request for adaptation resumption in the second transmission mode, positioning of the second equipment in reception of a tuning signal train according to the second mode of transmission.  n) in case of validation by the second equipment of the reception of said tuning signal train, adaptation of the second equipment to the second transmission mode.  o) transmission by the second equipment of a tuning signal train according to the second transmission mode to allow the first equipment to adapt to the second transmission mode.  p) analyzing by the first equipment the frequency of the unmodulated carrier signal of said tuning signal stream transmitted by the second equipment.  q) in case of recognition of this frequency, maintaining the positioning of the first equipment in the second mode of transmission.  r) in case of validation by the first equipment of the reception of said tuning signal stream transmitted by the second equipment, adaptation of the first equipment to the second transmission mode.  s) recovery according to the second transmission mode, exchanges of synchronization signal trains, possibly followed by application information without breaking the logical levels of the communication protocol of the two devices.  3. Method according to claim 1, characterized in that the equipment A and B are arranged to perform after the steps a) to g) the following steps  t) in case of non-recognition of the train of signals of agreement by the first equipment, renewal by the first equipment of the emission of the train of signals of agreement according to said mode of transmission.  u) steps c) to j)  4. Method according to claim 3, characterized in that it comprises the next step  v) in the event of non-recognition by the first device during step g) of the sequence u) of the agreement signal stream transmitted by the second device, last attempt made by the first device according to t) and u) before breaking the link between the two devices.  5. Method according to one of the preceding claims, characterized in that a said initialization (step a) is performed by detection by the first equipment of at least one train of erroneous synchronization signals, and in that during step b) said transmission mode is the transmission mode used previously.  6. Method according to one of the preceding claims, characterized in that a said adaptation is performed by setting the coefficients of a receiving filter of said equipment.  7. Method according to claim 6, characterized in that the equipment is arranged, after reception of the tuning signal trains, to freeze the coefficients of their reception filter after convergence of the coefficients of said reception filter and in that the devices are arranged to inhibit any possible modification of the reception filter coefficients during the exchange of the synchronization signal streams during communication so as to maintain, independently of the characteristics of the physical transmission medium, the reception filter coefficients values. calculated upon receipt of the last train of tuning signals.  8. Method according to one of the preceding claims, characterized in that the unmodulated carrier signal is an echo protection segment used on the satellite links.  9. Method according to one of claims 1 to 7, characterized in that said validation of the miss in communication by the equipment comprises transmitting a synchronization signal stream not starting with an unmodulated carrier signal, so not to degrade the useful rate during communication.  10. Equipment for implementing the method according to one of the preceding claims and comprising a line interface and a modem programmed by a sequencer, characterized in that said sequencer is arranged to  10-1) program the initialization of a resumption-adaptation.  10-2) programming the transmission by the modem of a tuning signal stream preceded by an unmodulated carrier signal, said tuning signal train constituting a readaptation request.  10-3) schedule the modem to detect at least one unmodulated carrier frequency at the beginning of a received tuning train, and to position the modem in a corresponding duplex transmission mode at said carrier frequency, so as to allow the modem to adapt according to the above modulation.  10-4) validating the half-duplex physical resumption-adaptation according to said transmission mode once the modem has transmitted and received in conformity said one signal stream during an exchange communication signal train tuning.  11. Equipment according to claim 10, characterized in that said initialization consists in programming the detection of a reception by the modem of a train of erroneous synchronization signals and in that the transmission according to 10-2 is carried out according to the same modulation as said wrong synchronization signal train.  12. Equipment according to claim 11, characterized in that the sequencer is arranged so that, when the modem is in reception mode, said detection of at least one unmodulated carrier frequency is performed continuously, and in case of a such detection performed while the equipment is in a half-duplex communication configuration, as well as a reception received in accordance with a tuning signal stream, for programming transmission by the modem a tuning signal stream preceded by an unmodulated carrier signal, according to the same modulation as said conformally received tuning signal stream, and validating an adaptation response according to that same modulation.  13. Equipment according to claim 11, characterized in that the sequencer is also arranged to validate said transmission of a 10-2 tuning signal stream when the modem has detected at least one erroneous synchronization train in one mode. transmission system, to perform at least one attempt to match according to the main transmission mode and in the event of failure to validate a said transmission of a signal stream according to 10-2 in a transmission mode half-duplex modulation more robust than the modulation of the main transmission mode.  14. Equipment according to claim 10, characterized in that the sequencer is arranged to validate said transmission of a tuning signal stream in a main transmission mode, to perform at least one attempt to match according to the mode. transmission, and in the event of failure to validate a said transmission of a 10-2 compliant signal stream in a fallback transmission mode in a more robust half-duplex modulation than the modulation of the initial transmission mode.  15. Equipment according to one of claims 10 to 14, characterized in that the sequencer is also arranged to manage the higher logic levels of the communication protocol with a disconnect timeout of greater duration than the execution of the resumption-adaptation process .