FR2771577A1 - Connection procedure enabling contact between modems connected to telephone network - Google Patents

Abstract

The procedures speed up the establishment of contact between remote stations. The procedure established connection between a calling station (MOc) and a called station (MOa) through a network (RTC). After dialling the number of a called station, there is a period of stabilisation (PS) for the transmission channel. The procedure then includes transmitting a sequence containing the capacity and configuration of the equipment (INF00c), followed by a phase of probing and marking during a period (PI) following the stabilisation period. This is following by a phase of interaction with the network when the capacity and configuration signal (INF00c) is not received by the called station within a given time. The procedure includes storing in memory channel modulation information about at least one item of equipment.

Description

Connection of terminal equipment
The present invention relates to a method of putting a terminal equipment calling into communication with a terminal equipment called through a switched telephone network.

In particular, the invention relates to equipment such as modems, at least one of which has modulation characteristics according to recent recommendation V.34, September 1994, of the
CCITT.

 For a V.34 modem, from the connection phase, the modem searches for characteristics of the transmission channel connecting it to a remote modem through the shared telephone network so as to optimize modulation parameters for the most selected modulation speed. big. This optimization consists in adapting, in the two modems, the bitrate of these, increasingly higher, to the relatively narrow bandwidth of certain still very numerous sections of the transmission channel through which data is exchanged between the modems, particularly at a user telephone line serving a user terminal equipped with one of the two modems.

Thus a bit rate between 2.4 and 28.8 or 33.6 kbit / s can be selected.

 This search for characteristics and therefore the exchange of modulation and transmission channel information is carried out each time that modems are put into communication and contributes to the relatively long duration of communication of modems corresponding to the progress of phases 1 to 4 of the recommendation V.34, of the order of 12 to 15 seconds.

 In addition, when one of the two modems is associated with an access point of the telephone network through which a data processing network and / or one or more servers is connected, the communication of the modems differs from the transmission of a page. from the modem called from the access point to the calling modem from the user terminal.

In practice, the user waits approximately 30 seconds to receive the home page.

 The present invention aims to provide a method of connecting two terminal equipment, such as modems, which significantly reduces the duration of connection of the equipment and consequently the transmission of a home page.

To this end, a method of putting a calling terminal equipment in communication with a called terminal equipment through a telephone switching means, is characterized in that, after dialing the call number of the called equipment and a period stabilization of a transmission channel between the equipment, it includes the steps of
- when the calling equipment is to be put in communication for at least a second time with the called equipment, send a capacity sequence and configuration of equipment from the calling equipment, and trigger a probing / tracking phase between the equipment in response to the sequence of capacity and configuration of equipment detected for a predetermined duration immediately following the stabilization period in the equipment called, and
- trigger an interaction phase with the network preceding the sounding / identification phase when the equipment capacity and configuration sequence is not received for the predetermined duration in the called equipment and when a tone signal is received by the calling equipment for a predetermined period.

 Thus, a first connection of the equipment takes place according to the invention substantially as according to the prior art, and is relatively long. On the other hand, from a second connection of the equipment, the first phase of interaction with the network is almost eliminated, and the numerous exchanges of tones, line test signals and modulation and transmission channel information resulting from measurements. test signals during a second conventional sounding / tracking phase are also suppressed according to the invention. In fact, all of this information is already stored in one of the devices. These deletions almost shorten the time it takes to connect the equipment.

 The first phase of interaction with the network is further reduced according to the invention if a call menu signal which is transmitted by the calling equipment and a common modes menu signal which is transmitted by the equipment called in response to the call menu signal each include only one byte to indicate a modulation mode available in the calling and called equipment, and / or if a common modes menu signal is emitted only once by the called equipment when the interaction phase with the network is triggered.

 Various variants are provided by the invention depending on whether one or both pieces of equipment store said information.

 According to a first embodiment, the probing / tracking phase is executed partially without exchanges of signals between the devices comprised between reception of respective first tones in the devices and the start of an equalizer and canceller conditioning phase d echo succeeding the probing / tracking phase when modulation and transmission channel information are pre-stored in at least one of the items of equipment. Initially during a first connection, the probing / identification phase is executed completely so as to store modulation and transmission channel information in said at least one of the items of equipment, when the calling equipment is to be put in communication. for the first time with the equipment called.

 According to a second embodiment, the modulation and transmission channel information is stored in at least one of the devices prior to any communication of the devices. In this embodiment, one of the devices knows that the transmission channel connecting it to the other device is frozen and therefore that the characteristics of the channel are known.

 According to the first or second embodiment, the partial execution of the sounding / identification phase substantially begins or ends with at least the downloading of said modulation and transmission channel information from the equipment having stored them to the other equipment.

Other aspects of the invention further contribute to reducing the duration of the communication of the equipment. An equalizer and echo canceller conditioning phase succeeding the sounding / tracking phase includes signals at lengths exactly defined by equipment manufacturers, and sequences of scrambler symbols of duration significantly less than 512T, or
T is a unit symbol interval. A final conditioning phase succeeding the equalizer and echo canceller conditioning phase includes sequences of scrambler symbols of duration significantly less than 512T.

 Waiting for an access point's home page is also reduced. This reduction is obtained for example when, the calling equipment being a modem associated with a user terminal and the called equipment being a modem associated with a network access point, the called modem begins to transmit a page of welcome to the calling modem before approximately the start of the sounding / tracking phase, preferably with modulation and transmission channel information.

Other characteristics and advantages of the present invention will appear more clearly on reading the following description of several preferred embodiments of the invention with reference to the corresponding appended drawings in which
- Figure 1 is a schematic block diagram of a telecommunications network showing a physical link between at least two terminal equipment such as modems
- Figure 2 is a schematic block diagram of the functional architecture of a modem
Figure 3 is a schematic block diagram of the hardware architecture of a modem
- Figure 4 is a diagram of a first phase of interaction with the network when calling and called modems are in V.34 mode, included in the method according to the invention;
- Figure 5 is a diagram of a first phase of interaction with the network when the calling and called modems are respectively in V.29 / V.27 and V.34 mode, included in the method according to the invention;
- Figure 6 is a diagram of a second phase of probing / tracking according to recommendation V.34;
- Figure 7 is a diagram of a second phase of probing / tracking which is shortened according to the invention;
- Figure 8 is a diagram of a third phase of equalizer conditioning and reduced echo canceller according to the invention; and
- Figure 9 is a diagram of a fourth phase of reduced final packaging according to the invention.

With reference to FIG. 1, a switched PSTN telephone network, such as the analog public telephone network connects several first terminal equipments, such as user terminals TU of which four are shown, and several second terminal equipments, such as Points d 'PA access of which only two are represented. The PSTN network conventionally includes telephone switches with independent routing
CAA to which are attached directly, or indirectly through local telephone switches (not shown), the first and second TU and PA equipment, and transit centers CT connecting the CAA switches to each other, so as to route telephone communications between the equipment.

 The equipment TU and PA are respectively connected to the switches CAA by respective modems MO, very often housed in the equipment, and through respective analog telephone lines LU and LP or increasingly digital. Each modem constitutes terminal equipment for data circuits.

 The user terminals TU are for example videotex terminals such as MINITEL (registered trademark) terminals, INTERNET terminals, mixed MINITEL / INTERNET terminals, personal microcomputers, and local network servers.

Each access point PA adapts signals to the videotex terminal protocol exchanged through the PSTN telephone network, to signals exchanged with ST data processing servers, if necessary through a data processing switching network.
RTI. A PA access point can be an Access Point
VIdéotex PAVI, and ST servers can be entities exchanging signals according to the CCITT X.25 recommendation through the packet communication network TRANSPAC (registered trademark).

For example, in France, an access point PA communicates a home page to a calling user terminal after having numbered in particular the call number of the PAVI access point 36-13, 36-15, or 36 -16, and before dialing the requested service code corresponding to the called server. According to another example, an access point PA can be a Micro PAM kiosk Access Point which gives access to one or more ST servers in a WEB site of the network.
INTERNET (registered trademark) exchanging signals according to PPP, TCP / IP communication protocols or
HTTP, as well as, if necessary, videotex servers according to the first example.

By way of nonlimiting example, reference will be made below to a preferred embodiment of the invention relating to two modems put in communication according to most of the requirements of CCITT Recommendation V.34, September 1994, in which the The invention provides improvements to reduce the duration of communication between the two modems. Recommendation V.34 is supplemented by the
CCITT Recommendation V.8, September 1994 for procedures for starting data transmission sessions. It will be assumed that communication is to be established between a calling user terminal whose modem is designated by MOc and a videotex access point called ("answering") whose modem is designated by MOa, through a transmission channel generally composed of an LU telephone line and an LP telephone line connected through at least one CAA switch of the PSTN network. More generally, each of the two modems can be sometimes calling, sometimes called, and other modems of type V. 29 or V.27ter can replace the modem calling MOc, as will be seen at the end of the description.

 The main characteristics of a V.34 modem recalled below with reference to Figure 2 are as follows. The MO modem can operate in duplex or half-duplex mode through an analog interface 1 with the PSTN network and a digital interface 2 with the respective terminal TU, PA.

The network interface 1 separates the line, very often still with 2 wires, into a transmission channel to the network and a reception channel from the network and comprises between these channels an electric echo canceller. The transmission channel of the MO modem constitutes the transmitter of the modem while the reception channel constitutes the receiver of the modem.

 The transmitter essentially comprises from the terminal interface 2, a coding and conversion circuit 3, a non-linear coder 4, a modulator 5 with amplitude modulation in quadrature QAM, a pre-emphasis circuit 6, and a digital converter. analog 7.

 In circuit 3, a scrambler encrypts the data transmitted by the terminal according to a predetermined generator polynomial. Then a trellis coder composed of a convolutional coder improves noise immunity by selecting a sequence of subsets in a partitioned signal constellation. The trellis encoder is 4-dimensional and is used for all rates in a feedback structure in which the input signals of the trellis encoder are determined from point states that are applied to a precoder. Precoding in the precoder is a non-linear equalization method used to reduce the increase in equalization noise due to amplitude distortion.

The equalization is carried out in circuit 3 by means of precoding coefficients supplied by the remote modem through a decoder 10 in the receiver.

 In circuit 3, a coefficient converter includes a superframe conditioner and a differential encoder. The superframe conditioner maps the data bits of point states into a multidimensional signal constellation, which involves partitioning a bidirectional signal constellation into rings containing an equal number of points. Constellations are subsets of a 960-point superconstellation. Constellation conditioning improves noise immunity by introducing a non-uniform bidirectional probability distribution for the signal points to be transmitted. The degree of conditioning is a function of the degree of expansion of the constellation. The differential encoder converts specific data bits to an integer according to an algorithm defined in recommendation V.34.

 The non-linear encoder 4 improves immunity to distortions in the vicinity of the perimeter of the signal constellation by introducing non-uniform spacing of divalent point states (2D).

 The modulator 5 and a demodulator 9 in the receiver implement a quadrature amplitude modulation (QAM) with synchronous online transmission at different switchable modulation rates, including the mandatory modulation rates of 2400, 3000 and 3200 baud as well as the optional baud rates of 2743, 2800 and 3429 baud. Synchronous primary bit rates are achievable from 28,800 bit / s to 2,400 bit / s.

 The pre-emphasis circuit 6 is a linear equalizer in which the spectrum of the signal to be transmitted is modeled in order to compensate for the amplitude distortion. In circuit 6, a pre-emphasis filter is chosen by means of a filter index supplied by the remote modem, via the decoder 10.

 The receiver comprises, following an analog-digital converter 8 connected to the network interface 1, the demodulator 9 and a decoder 10 having functions reciprocal to those of circuits 5 and 3, 4.

A preferred hardware architecture of a modem
MO according to the invention is shown diagrammatically in FIG. 3. It comprises two modules organized around a microcontroller 11 connected to EEPROM and RAM memories 12 and 13 and to a serial interface 14 for terminal or access point, and around a digital processor DSP (Digital Signal Processor) 15 connected to several EEPROM memories 16 (Modem Data Pump) and a RAM memory 17. The processor 15 is connected to the microcontroller 11 by registers 18 and a BU bus and a telephone line of the PSTN network by a line interface 19. The modem also includes a DTP (Digital Talk coprocessor) speech processor 20 connected to the PSTN network through an audio interface 21 and to the microcontroller 11 by the BU bus. As will be seen according to the embodiments of the method of the invention, additional data (INFO1) are downloaded into the EEPROM memory 16 of the processor
DSP. These participate, among other things, in the modulation, coding, demodulation and decoding functions.

The connection procedure according to the
Recommendation V.34, for example, between a modem calling from an MOc terminal and a modem called from an access point MOa in duplex mode through the PSTN network comprises four phases. Although this example is referred to in the following description, the calling modem can be that of a PAVI access point and the called modem can be that of a user terminal TU.

 Phase 1 corresponds to an interaction with the network, that is to say signal exchanges between modems through the PSTN network for the establishment of a data transmission session before the exchange of conforming signals recommendations for modems. Phase 1 can be omitted according to the invention if the link between the modems is already pre-established, in particular when the link between the modems is specialized, or the connection according to a first modulation is already known, or during a resynchronization, as we will see it later.

 Phase 2 performs sounding and tracking operations on the transmission channel between the two modems. Parameters containing capacity information and modulation modes are routed in specific sequences.

 Phase 3 operates the conditioning of the equalizer and the echo canceller in each of the modems. In addition, an adjustment of the constellation, according to which the signals of phase 4 are exchanged, is carried out.

 Phase 4 performs a final conditioning of each modem in duplex mode and the exchange of last modulation parameters in data mode, for example the data exchange rate in transmission mode.

 According to a first connection state, the calling modem (“calling”) MOc is connected for the first time to the telephone line of the user serving it and must be put in communication in duplex mode with the modem called MOa (“ answering ") from the respective PA access point, following a" cut "or" interruption "in the transmission channel between the modems, or a first installation, repair or disconnection / connection of the MOc modem. In this case, phase 1 is modified according to the invention and is carried out so that at least one of the two modems, preferably the modem called MOa of the access point stores the template of the transmission channel at the next phase 2. The memorization of the transmission channel template makes it possible not to execute phase 1 when the MOc modem is next connected to the MOa modem which is then in a second connection state, and thus considerably reduce the duration of the porting of subsequent modems.

First connection state: phases 1 and 2
With reference to FIGS. 4 and 5, after manual or semi-automatic numbering (presence of the user) of the call number of the access point PA associated with the modem called MOa by the user terminal
TU associated with the calling modem MOc, the called modem does not wait more than a predetermined period of silence PS for line stabilization to take the telephone line. For example, the period PS is one second when the calling and called modems are attached to the same telephone switch CAA. Then the modem called MOa conditions its receiver to receive a first sequence of capacity and modem configuration INFO0c which is characterized by a carrier frequency of 1200 Hz and which is sent by the modem calling MOc at the start of phase 2 (Figure 6 or 7 ).

According to this first connection state, a register
RM in the calling modem MOc associated with the call number of the called modem, which had been set to "0" following the prior disconnection of the modem
MOc, indicates that the connection to be established with the modem
MOa is a first connection, and therefore, no first sequence INFO0c is sent from the modem calling MOc and phase 1 must be carried out. Thus, at the expiration of a predetermined period PI, typically a second following the line stabilization period PS, the modem called MOa has not detected any sequence INFO0c and sends a modified tone signal ANSam with a carrier of 2100 Hz having phase reversals at periodic intervals of 450 ms, the calling modem not transmitting a CT call indicator signal for a manual or semi-automatic call, and the receiver of the calling modem MOc is conditioned to receive the signal ANSam for a predetermined period PK.

 According to a first embodiment, the calling modem MOc only has V.34 (or V.32bis or V.32) modulation, as shown in FIG. 4.

 As soon as the 2100 Hz carrier receives the ANSam tone signal, the calling modem MOc validates this signal for a validation period Te of between 500 ms and 1 s. The validated signal ANSam thus comprises at least one phase inversion. After the duration Te of validation of the signal ANSam, the calling modem MOc begins to transmit a sequence of signal of menu of call CM, which indicates according to the recommendation V.8, the modulation modes available in the modem MOc, and to condition its receiver for detecting a JM common mode menu signal sequence which indicates, according to recommendation V.8, the modulation modes common to the modems in response to the CM signal.

In this first embodiment of the invention where the MOc and MOa modems are in modulation mode
V.34, the CM and JM sequences each have only one byte which indicates the available modulation mode and which is confused with the first of three bytes including the V.34 modulation mode according to table 4 of recommendation V. 8. In addition, the optional protocol category byte according to recommendation V.8 and the RTGC access category byte useful for indicating cell-type access are not transmitted.

 Upon receipt of the first CM sequence, the modem called MOa transmits a single JM sequence, instead of two identical JM sequences according to recommendation V. 8. After having received said single JM sequence, the modem calling MOc transmits an end signal CJ indicating the end of the CM signal.

The above two characteristics of the signals
CM and JM according to the invention reduce the duration of phase 1.

 The calling modem remains silent for 75 ms before proceeding to phase 2. The transmission of the JM signal continues in the modem called MOa until reception of the signal CJ. The modem called MOa remains 75 ms silent before proceeding to phase 2.

According to a second embodiment, the modem calling MOc has V.34 and V.29 modulations or
V.27, as shown in Figure 5.

 As before, in the case of a manual or semi-automatic call (presence of the user), the calling modem MOc does not emit a call indicator signal CT. When the calling modem enters the "first" connection phase with the called modem, the called modem MOa does not wait for more than the sum of the line stabilization period PS and the first sequence detection period PI.

 At the expiration of the period PI, without transmission of the first sequence INFO0c, and upon reception of the carrier at 2100 Hz of the tone signal ANSam for at most the predetermined duration PK, the modem calling MOc having V.29 modulation or V.27 validates the ANSam or ANS tone signal in 300 ms followed by a silence period of 150 ms. After validation of the ANSam signal, the calling modem MOc begins to transmit an appropriate TL long train sequence.

 After having received the long train learning sequence preceded by the characteristic carrier recognized by filtering, the modem called MOa transmits a corresponding long train. After receiving the corresponding long train, the calling modem MOc sends a modem protocol connection request to which the called modem MOa responds.

In the context of recommendation V.29 or
V.27, the protocol connection is preferably continued by short train and ends with the sending of the home page by the called modem followed by an identification request from the calling terminal MOc.

After reception of the home page with request for identification of the terminal, the calling modem keeps a silence of 75 ms before proceeding to phase 2. In response to the home page, the modem called MOc keeps a silence of 75 ms before going to phase 2.

 It is recalled below with reference to FIG. 6 the phase of probing / location 2 which is carried out entirely when, in the first connection state, the two modems ignore in particular the characteristics of the transmission channel between the modems through the PSTN network , resulting from measurements of test signals, such as attenuation, attenuation distortion and group delay time distortion as a function of frequency.

During the 75 ms silence period which ends phase 1 (Figure 4 or 5), the receiver of the calling modem MOc is conditioned to the reception of an INFOOa sequence and to the detection of a first tone A. After the period of 75 ms of silence, the calling modem cyclically sends a sequence of capacity and modem configuration
INFO0c, followed by a first tone B. The sequence
INFO0c, like the sequence INFOOa transmitted by the called modem, indicates in particular to the remote modem a selected modulation speed, and possibilities to transmit the lower and higher carrier frequencies for certain modulation speeds. Tones A and B are transmitted at 2400 Hz and 1200 Hz respectively. After receiving the sequence INFOOa, the calling modem MOc stops the cyclic transmission of the sequence INFO0c and conditions its receiver to detect the first tone A and a first inversion of Next phase A of tone A. After detecting the reverse phase A tone, the modem calling MOc emits a first phase B tone inversion
B. Tone B is emitted for an additional 10 ms.

 Similarly, during the 75 ms period of silence which ends phase 1, the modem receiver called MOa is conditioned to receive the sequence INFO0c and to detect the first tone B.

After the 75 ms period of silence, the MOa modem sends the sequence INFOOa, followed by the first tone A. After receiving the sequence INFO0c, the receiver of the MOa modem is conditioned to detect the first tone B. After detection of the first tone B and emission of the first tone A for at most 40 ms, the called modem transmits the first tone with reversed phase A and conditions its receiver to detect the first tone with reversed phase B.

 As will appear later in FIG. 7, the first part of phase 2 presented above only constitutes phase 2 which is considerably shortened according to the invention when one of the modems knows characteristics of the transmission channel between the modems (second connection state).

 In the case of the first connection state, phase 2 is continued normally. After the transmission of the first reverse phase tone B, the modem calling MOc remains silent and conditions its receiver to detect a second reverse phase tone A. After detecting the second reverse phase tone A, the modem calling MOc calculates the round trip delay between modems, and after detection of the first reverse phase tone B, the modem called MOa also calculates the round trip delay. The estimation of each of these round trip propagation times is the time interval which approximately separates the emission of a respective inverted phase tone B, A and the reception of another respective inverted phase tone A, B. The called modem then transmits the second reverse phase tone A, the transmission of which is delayed until reception of the first reverse phase tone B.

The calling modem MOc having detected the second tone A then conditions its receiver to detect first line test signals L1 and
L2 which are periodic signals each composed of sinusoidal tones between 150 Hz and 3750 Hz and which are transmitted by the modem called MOa after the transmission of the second inverted phase tone
A. These test signals make it possible to determine the characteristics of the transmission channel, and thus of the modulation parameters of the selected mode. The calling modem MOc receives the signal L1, for 160 ms and the signal L2 for a period not exceeding 500 ms, then emits a second tone B and conditions its receiver for the detection of a second tone A and a third tone to phase A inversion which are transmitted by the modem called MOa after the transmission of the first line test signals L1 and L2.

 After detecting the second tone A and the third phase inversion tone A, the calling modem MOc emits a second inverted phase tone B. The calling modem then emits second line test signals L1 and L2, then conditions its receiver to detect a third tone A.

When the second tone B is detected by the modem called MOa which has received the local echo of the first signal L2 for a predetermined period, the modem called emits the second tone A and the third tone A. After a silence, the modem MOa conditions its receiver to detect the second reverse phase tone B, then the second line test signals L1 and L2 emitted by the modem
MOc. The called modem receives the second L1 signal for 160 ms and the second L2 signal for a period not exceeding 500 ms.

 The modem called MOa then emits the third tone A and conditions its receiver for the detection of an INFOlc sequence. Once the calling modem has detected the third tone A and has received the local echo of the second signal L2 for a predetermined period, the calling modem sends the sequence INFOlc. After having sent the INFOlc sequence, the calling modem remains silent and then conditions its receiver for the detection of an INFOla sequence sent by the modem called MOa in response to the reception of the INFOlc sequence. Then the modems go to phase 3.

 The sequences INFOlc and INFOla transmitted by the modems MOc and MOa indicate in particular power levels in transmission and reception, lengths of conditioning signals of echo canceller MD transmitted during the following phase 3, indices of spectrum of filter pre-emphasis, the use of the high carrier frequency, a projected maximum symbol rate, the modulation speed to be used in the directions from the called modem to the calling modem and from the calling modem to called modem, and relevant test results the choice of a final modulation speed so as to determine in particular equalizer coefficients and the selected symbol rate.

According to the invention, after a first connection during which phase 1 was executed according to FIG. 4 or 5 and phase 2 was carried out as described above, most of the information exchanged between the modems during these two phases are kept for other shortened subsequent communications according to the invention. This information is in particular the common modulation modes in the common mode menu signal JM according to FIG. 4, or in the protocol connection signals according to FIG. 5, and the characteristics of the transmission channel between the modems and the operating parameters. modems contained in the INFOlc sequences and
INFOla. They are preferably stored in each of the modems MOc and MOa at a memory address corresponding to the other modem respectively, as indicated in Mlc, Mla in FIGS. 4 and 5 and M2c, M2a in FIG. 6.

Second connection state: phases 1 and 2
According to a second connection state, the register
RM of the calling modem MOc associated with the call number of the called modem is in the "1" state, which means that the MOc modem has previously established at least a first connection with the MOa modem, without intermediate disconnection of the modem MOc of the respective user line. In this case, immediately after dialing the server call number associated with the MOa modem and the PS stabilization period, the calling modem MOc cyclically transmits the capacity sequence and modem configuration INFO0c which signals the start of phase 2 , without performing phase 1, that is to say the start-up phase according to recommendation V.8, or the protocol connection phase according to recommendations V.29 or V.27.

According to a first variant, if the modem called
MOa ignores any sequence INFO0c during the predetermined period, that is to say is not a modem according to the invention, it transmits the tone signal ANSam so that as soon as it is received by the modem calling MOc for the period PK, the cyclic transmission of the sequence INFO0c is stopped and phase 1 is carried out normally.

 During the second communication succeeding the first or any other subsequent communication according to a second variant, the modems know the characteristics corresponding to the information stored and it is not necessary according to the invention to transmit them.

In this case, as shown in FIG. 7, phase 2 is shortened by suppressing the transmissions of the second tone B, of the second reverse phase tone B, of the second line test signals L1 and L2 and of the sequence INFOlc from the modem calling MOc, after receiving the first phase inversion A tone, and suppressing the transmissions of the second phase inverted A tone, of the first line test signals L1 and L2, of the second tone A, the third phase inverted tone A, the third tone A and the sequence INFOla from the modem called MOc, after reception of the first phase inversion tone B.

According to a third variant, only one of the modems MOc and MOa records said information after the first connection. During the second connection, if the calling modem
MOc has already recorded said information at a memory address corresponding to the called modem, the MOc modem reads said information to download it into the called modem MOa after the emission of the first reverse phase tone B, at the end of phase 2 , as shown in TCc in FIG. 7. Similarly, during the second connection, if the modem called MOa has already saved said information at a memory address corresponding to the calling modem, the modem MOa reads said information to download it in the modem calling MOc after the emission of the first reverse phase A tone, at the end of phase 2, as shown in TCa in FIG. 7.

According to a fourth variant, the modem called
MOa at the videotex access point PA and / or the calling modem MOc at the user terminal TU previously records modulation information as well as "theoretical" characteristics of the transmission channel between the modems across the network
PSTN, before any modem communication.

This recording is carried out either locally by means of a microcomputer or the terminal itself, or through the corresponding telephone line.

 From the first communication with RM = "O", phase 2 is then carried out as shown in FIG. 7 if the two modems have said information or, according to the third preceding variant, if only one of the modems has said information . This fourth variant is particularly advantageous, either when the calling modem is dedicated to calling only a single called modem, that is to say a predetermined access point, or when the called modem and the calling modems capable of 'call the called modem are connected to a common CAA home switch since the transmission channel depends almost only on the user line LU serving the terminal TU associated with the calling modem MOc.

 The reduction in the duration of phase 2 with elimination of phase 1 according to the invention shown in FIG. 7 is approximately of the order of half the duration of phase 2 shown in FIG. 6.

Phases 3 and 4
Phase 3 of equalizer and echo canceller conditioning begins with successive transmissions of signals S, s, MD, S, S, PP, TRN and J from the modem called MOa, then with successive transmissions of signals S to J similar to the previous signals from the modem calling MOc, as shown in FIG. 8. According to the invention, each of the signals
MD and TRN is reduced.

 The MD (Manufacturer-Defined) signal is defined by the manufacturer of the respective modem for the conditioning of its echo canceller, and is determined by an integer between 0 and 127, that is to say which can be equal to zero, contained in the INFOlc sequence and defining the duration of the MD sequence in 35 ms increments. The duration of this signal, defined by the manufacturer to condition the echo canceller, must not exceed N times 35 ms according to recommendation V.34. According to the invention, the signal MD is predefined to the exact length, and / or according to the preceding variants, is prerecorded in each modem or at least in one of the modems at an address corresponding to the other modem.

The TRN signal is a sequence of symbols produced by injecting binary "1s" transmitted to the input of the scrambler to improve the conditioning of the echo canceller and the adjustment of the equalizer. According to the invention, the duration of the signal
TRN is less than 512T provided by the recommendation
V.34 and does not exceed NT, where N is an integer for example equal to 128, and T is the tetravalent unit interval of a frame relating to the speed of modulation previously negotiated. As with the MD signal, depending on the variant, the coefficients of the equalizer can be downloaded locally or by the corresponding telephone line in the modem.

After having received the sequence J indicating the size of the constellation used by the remote modem for the transmission of the sequences TRN, MP,
MP 'and E during the final conditioning in the next phase 4, the called modem or the calling modem waits at most 200 ms, instead of 500 ms provided by recommendation V.34, before sending a signal S setting the constellation axes.

The final conditioning phase is shown in FIG. 9. After detecting the signal S and the signal S, corresponding to the signal S after phase inversion, transmitted by the modem called Moa, the modem calling MOc stops transmitting the signal J transmitting a single sequence J 'at the end of sequence transmission
J. Then to complete the conditioning, each MOc modem, MOa in particular transmits a TRN sequence of phase 4 whose duration does not exceed MT, where M is an integer, for example equal to 10, instead of 512T provided for in recommendation V .34.

 Between the start of phase 1, after dialing the telephone number of the access point associated with the modem called MOa, and the end of the final conditioning phase 4, the improvements brought about by the invention reduce the duration of the physical and protocol connection approximately half of the duration envisaged when all the phases of the recommendation V.34 are carried out, that is to say a gain of at least six seconds approximately.

 The shortening of the duration of the connection of two modems is also advantageous in the event of recovery on error. For example, during phase 3 or 4, when the tone A is detected by the modem calling MOc, or when the tone B is detected by the modem called MOa, the modem having detected the respective tone initiates a repackaging by deactivating a "ready to send" circuit 106, locking a "received data" circuit 104 and passing to the probing / location phase 2, and thus again performing phases 3 and 4 or phase 4. This repackaging can also result from a loss of the carrier by one of the modems for a short predetermined duration, including resulting from a general cut in the transmission channel between the modems, without requiring a total reset of the modems by passing to the first connection state (RM = "0") according to the invention.

 After the end of phase 4, the home page can be conventionally sent by the modem MOa from the access point called to the modem calling MOc.

 However, as already said with reference to FIG. 5, at the end of the preliminary identification phase 1, for example relating to a calling modem of V.29 or V.27 type as shown in FIG. 5, ie after the exchange of protocol connection signals and storage of these, the modem called MOa at the access point PA transmits the content of a home page AC, then additional information which promotes the reduction of the V.34 / V.34-96 connection time for subsequent modem connections. This additional information corresponds to the information on the characteristics of the transmission channel between modems and the operating parameters of the modems according to the variants of the invention, and can be transmitted substantially until the reception of the home page has been completed in the modem calling MOc. The information exchange INFO at the end of phase 2 according to FIG. 7 can thus be located at the end of phase 1, that is to say substantially at the start of phase 2, according to FIG. 5.

During the transition from standard V.29 to standard
V.34, display of data on the terminal screen
TU is artificially slowed down without causing discomfort for the user. For example, the data corresponding to the home page can be transmitted in three seconds, but displayed between three and five seconds. The time thus recovered is used to mask the process of establishment at high speed and therefore the transaction, from additional information on the home page.

 The additional information, sent by the download server, is contained in a call packet, in accordance with the X25-3 protocol in V29 (or V.27ter) modulation. They contain elements on the characteristics of the remote equipment and the transmission channel. This information is interpreted by the terminal modem which can have these parameters by default or not, depending on the variants of the invention. The distinction is made when identifying the terminal at connection in V.29 (or V.27ter). The Moa modem adapts to the dual MOc modem associated with the terminal. Synchronization of modems after switching to V.34 or V.34-96 can thus be initiated. Convergence, that is to say the definitive connection of modems in V.34 (or V.3496), is then established more quickly. The transition from a V.29 connection to a V.34 or V.34-96 connection, by relying on the shortening of the connection phases, is therefore essentially based on bringing together modems which are known, the remote modem. was identified beforehand, which are selected, the transmission channel being identified by the downloaded or default coefficients, and which are paired, the modems being able to synchronize quickly.

Claims (9)

 - trigger an interaction phase with the network (phase 1) preceding the sounding / identification phase (phase 2) when the sequence of capacity and equipment configuration (INFO0c) is not received during the predetermined period (PI) in the called equipment (MOa) and when a tone signal (ANSam) is received by the calling equipment (MOc) for a predetermined period (PK).  - when the calling equipment (MOc) is to be put in communication for at least a second time with the called equipment (MOa), send a sequence of capacity and configuration of equipment (INFO0c) from the calling equipment, and trigger a probing / identification phase (phase 2) between the devices in response to the equipment capacity and configuration sequence (INFO0c) detected for a predetermined duration (PI) immediately following the stabilization period (PS) in the device called, and  1 - Method for establishing communication between a calling terminal equipment (MOc) and a called terminal equipment (MOa) through a switching means (RTC), characterized in that, after dialing the equipment's call number called and a stabilization period (PS) of a transmission channel (LU, PSTN, LP) between the devices, it includes the steps of  2 - Method according to claim 1, according to which a call menu signal (CM) which is transmitted by the calling equipment (MOc) and a common modes menu signal (JM) which is transmitted by the equipment called (MOa) in response to the call menu signal each include only one byte to indicate a modulation mode available in the calling and called equipment.  3 - Method according to claim 1, according to which a common modes menu signal (JM) is transmitted only once by the called equipment (MOa) when the interaction phase with the network (phase 1) is triggered.  - complete execution of the sounding / tracking phase (phase 2) so as to store modulation and transmission channel information in at least one of the devices, when the calling device is to be put into communication for the first time with the equipment called.  - partial execution of the sounding / tracking phase (phase 2) without signal exchanges (B, B, L1, L2, INFOlc; A, L1, L2, A, A, A, INFO1) between the equipment between reception of the first respective tones (A, B) in the equipment and the start of an equalizer and echo canceller conditioning phase (phase 3) succeeding the sounding / tracking phase when modulation and transmission channels are pre-stored in at least one of the devices (MOc, MOa), and  4 Method according to any one of claims 1 to 3, comprising  5 method according to any one of claims 1 to 4, comprising the storage of modulation and transmission channel information in at least one of the equipment prior to any communication of the equipment.  6 - Process according to claim 4 or 5, according to which the partial execution of the probing / tracking phase (phase 2) substantially begins or is terminated by at least the downloading of said modulation and transmission channel information (INFOlc; INFOla) from the equipment that memorized them to the other equipment.  7 method according to any one of claims 1 to 6, comprising an equalizer and echo canceller conditioning phase (phase 3) succeeding the sounding / tracking phase (phase 2) and including signals ( MD) at lengths exactly defined by equipment manufacturers, and symbol sequences (TRN) for scramblers of duration significantly less than 512T, where T is a unit symbol interval.  8 Method according to any one of claims 1 to 7, comprising a final conditioning phase (phase 4) which succeeds an equalizer and echo canceller conditioning phase (phase 3) following the phase of sounding / tracking (phase 2) and which includes symbol sequences (TRN) for scramblers of duration significantly less than 512T, where T is a unit symbol interval.  9 Method according to any one of claims 1 to 8, according to which the calling equipment is a modem (MOc) associated with a user terminal and the equipment called is a modem (MOa) associated with a point of network access (PA) (PSTN), and the called modem (MOa) begins to transmit a home page (AC) to the calling modem (MOc) before about the start of the survey / tracking phase (phase 2), preferably with modulation and transmission channel information.