METHOD OF QUICK CONNECTION OF PSTN MODEMS AND PSTN MODEM WITH FAST CONNECTION ACCORDING TO SUCH METHOD

Abstract

A method of quick set up of PSTN modem connection is proposed. The method of quick set up of PSTN modem connection comprises: setting access to the data channel, identifying channel characteristics, configuring PSTN modems depending on the characteristics of the channel, configuring echo compensators of PSTN modems, negotiating the connection protocol and data transfer between PSTN modems according to the configuration using the agreed protocol where: data transmission is carried out in duplex mode with the separation of signals of reception and transmission by echo compensation, identification of channel characteristics and adjustment of the echo compensator of each of the PSTN modems is performed, respectively, when receiving and transmitting at least one training sequence by each PSTN modem, access to the data channel is carried out by sending call by PSTN modem, which contains the training sequence and connection parameters for negotiation, where using a multiple access protocol, when each of the PSTN modems is connected to the data channel asynchronously, without agreeing on the time of connection and without the need to pre-allocate the roles of calling and responding modems.

Claims

1. A method of quick set up of PSTN modem connection, which includes setting access to the data channel, identifying channel characteristics, configuring PSTN modems depending on the characteristics of the channel, configuring echo compensators of PSTN modems, negotiating the connection protocol and data transfer between PSTN modems according to the configuration using the agreed protocol where: data transmission is carried out in duplex mode with the separation of signals of reception and transmission by echo compensation, identification of channel characteristics and adjustment of the echo compensator of each of the PSTN modems is performed, respectively, when receiving and transmitting at least one training sequence by each PSTN modem, access to the data channel is carried out by sending call by PSTN modem, which contains the training sequence and connection parameters for negotiation, where using a multiple access protocol, when each of the PSTN modems is connected to the data channel asynchronously, without agreeing on the time of connection and without the need to pre-allocate the roles of calling and responding modems.

2. The method according to claim 1, characterized in that the connection protocol negotiation includes role allocation, signal parameter negotiation, and data rate.

3. The method according to claim 1, characterized in that after switching on, each of the PSTN modems enters the call reception mode, and in the absence of a call, each PSTN modem transmits a call sequence, and then enters into the mode of receiving response.

4. The method according to claim 1, characterized in that an independent assignment of a pause after a call by each PSTN modem (TimeOut) is performed, whereas the pause is defined as a random variable that has a distribution of the baseline value close to normal, the mean value of which is preferably greater than the expected delay in the channel (round trip), and is within the standard deviation less than the mathematical expectation of time delays.

5. The method according to claim 1, characterized in that the conditions of normality of the random variable distribution and standard deviation are determined by PSTN-modem on the basis of machine learning algorithm.

6. The method according to claim 1, characterized in that after receiving the response, the PSTN modem determines mutually acceptable parameters of the data signal and the data rate, followed by the transmission of the sequence of confirmation of the selected parameters to another PSTN modem and the start of information transmission at the agreed rate.

7. The method according to claim 1, characterized in that random numbering of each call and ignoring the answer with the number that coincides with the number of the last call is applied.

8. The method according to claim 2, characterized in that the distribution of roles includes assigning the modem that first received the call as the answering modem, followed by this modem sending a message in response to the modem from which the call was received.

9. PSTN modem with fast connection set up, which includes a means of communication with a telephone line, modulator/demodulator, echo compensator, digital-to-analog converter and an analog-to-digital converter, and a series-connected means of data transmission in duplex mode, scrambler, deserializer, at least one encoder, transmission filter, and series-connected input filter, equalizer, at least one decision-making device, descrambler and serializer, whereas further comprising a automatic connection protocol, the input of which is connected to the output of the serializer and the output of the decoder, and the output of the automatic connection protocol is connected to the data transmission means in duplex mode, and the automatic connection protocol is suitable for alternating the phases of connection set up and installation of connection protocol data depending on the results of the evaluation of the characteristics of the channel by the modem and the information received from the modem from which the response was received.

10. PSTN modem according to claim 9, characterized in that the switch is used as a means of data transmission in duplex mode.

11. PSTN modem according to claim 10, characterized in that the automatic connection protocol is connected to the switch to transmit switch control data.

12. PSTN modem according to claim 11, characterized in that the automatic connection protocol is connected to the switch to transmit connection protocol data.

13. PSTN modem according to claim 11, characterized in that the connection protocol data includes the connection phase and data rate and the parameters of the data signal.

14. PSTN modem according to claim 9, characterized in that the said modem additionally contains a frequency response corrector, and the input of the automatic connection protocol is connected to the output of the frequency response corrector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention is illustrated by an example of embodiment of a fast PSTN modem with a quick connection and a method of fast connection between such PSTN modems. The example is illustrated by the following images:

[0028] FIG. 1 is a block diagram of a PSTN modem with fast connection,

[0029] FIG. 2 is a schematic drawing of the connection protocol of two PSTN modems,

[0030] FIG. 3—constellations of signals 4PM (A) and 8PM (B), which are used in the connection protocol of PSTN modems,

[0031] FIG. 4 is a state transition diagram (STD) describing the connection protocol of two PSTN modems.

[0032] These examples and the images used do not limit other possible embodiments of the invention, but only explain its essence and confirm the feasibility.

DETAILED DESCRIPTION OF THE INVENTION

[0033] The PSTN modem includes a switch (1) as a means of transmitting data in duplex mode, the input of which is fed with data for transmission in the form of a bit stream. The output of the switch (1) is connected to a series-connected scrambler (2), deserializer (3), encoding means: a lattice encoder (4) and a signal encoder (5) and a low-frequency transmission filter (6). The output of the low-frequency transmission filter (6) and the reference frequency generator (7) are connected to the modulator. The output of the modulator is connected to a digital-to-analog converter, DAC (8). The output of the DAC (8) is connected via differential circuit (9) with telephone line PSTN (10). The output of the differential circuit (9) is connected to an analog-to-digital converter, ADC (11). The PSTN modem also includes an echo compensator filter (12), the input of which is connected to the modulator and the unit for calculating the echo suppression coefficients (13), the frequency response corrector (14), and a series-connected input filter (15), equalizer (16) Viterbi decoder (17) as a decision-making device, descrambler (18) and serializer (19). A band-pass adaptive filter is used as the input filter (15).

[0034] The PSTN modem further comprises an automatic connection protocol processor (20), the input of which is connected to the output of the serializer (19), the output of the Viterbi decoder (17) and the input of the frequency response corrector (14). The output of the automatic connection protocol processor (20) is connected to the switch (1) for transmitting control data of the switch and for transmitting data of the connection protocol. The automatic connection protocol processor (20) is a processor device suitable for alternating connection establishment and connection protocol data depending on the results of the modem channel evaluation and the information received from the modem from which the response is received.

[0035] To transmit data over the telephone line, the bitstream obtained through the switch (1) is scrambled using a scrambler (2) and grouped into groups of several bits in the deserializer (3). The number of groups depends on the transmission rate and is encoded by the lattice encoder (4) in accordance with the rules of convolutional coding. Each symbol from the output of the lattice encoder (4) is displayed in the signal encoder (5) in the symbols of the signal constellation (see FIG. 3). The symbols are represented by complex numbers that reflect the amplitude and phase of the samples of the symbol during data transmission. Samples corresponding to the transmitted symbols are fed to the input of the low-frequency transmission filter (6). From the output of the low-frequency transmission filter (6), the samples in the integrated view are fed to the modulator. In the modulator, the complex signal samples are multiplied by sinusoidal and cosine samples from the reference frequency generator (7), respectively. At the output of the modulator, the orthogonal components of the signal are summed and fed to the DAC (8), from which through the differential circuit (9) are transmitted to the telephone line (10).

[0036] The signal from the transmitter of the correspondent through the telephone line (10) is allocated by the differential circuit (9) and is fed to the ADC (11). The ADC (11) converts the analog signal into a sequence of real numbers that reflect the value of the analog signal at the time of sampling. The input sequence is filtered in the frequency response corrector (14) in order to increase the signal-to-noise ratio. From the output of the frequency response corrector (14) the signal is fed to the demodulator, which converts the sequence of real numbers into a sequence of complex numbers, which reflects the value of the demodulated signal (analytical representation). The demodulated signal passes through the equalizer (16), which adjusts the phase and frequency characteristics of the channel and enters the Viterbi decoder (17). Next, the character stream is descrambled in the descrambler (18) and converted into a bit stream through the serializer (19). In this case, the automatic connection protocol processor (20) provides alternation of connection phases and setting of connection parameters (in particular, data transmission rate) depending on the results of evaluation of channel characteristics by the modem and information received from the correspondent modem.

[0037] The operation of a PSTN modem in duplex mode can be divided into two periods: connection set up and data exchange. The connection is established from the moment the command is received from the terminal to set up a connection. The two modems are considered equivalent devices, but the modem that received the command to set up the connection is considered the calling modem. Such a modem starts sending call signals at random intervals. The modem that first accepted the correspondent's modem call answers the call. In the process of transmitting a call and answering a call, each of the modems configures the echo compensator. In the process of receiving a call and receiving a response to a call, each of the modems evaluates the frequency and statistical parameters of the channel, adjusts the frequency response corrector (14) and the input filter (15).

[0038] The connection set up sequence can be represented as alternating the following phases of the modem operation and the operation phases of the modem transmitter shown in the PSTN modem operation diagram in FIG. 2. On FIG. 2 and in the following explanation of the operation of the modem and modem transmitter, the following indications are used: [0039] S—sequence ABABAB . . . length of 32 clock intervals (32T); [0040] S—sequence CDCDCD . . . length 8T; [0041] TRN—scrambled units at a speed of 4800 bps, here the flow rate (sequence of two bits) is not encoded, not scrambled, and directly displayed in state A, B, C or D (FIG. 3); [0042] RC—signals selecting the speed of the calling modem; [0043] RA—answering modem speed selection signals; [0044] EC—the end of the speed selection signal by the calling modem; [0045] EA—the end of the speed selection signal by the answering modem; [0046] B—executive units, which are scrambled and encoded in the same way as the data transmitted after, [0047] S, ¬S, TRN, ¬TRN are transmitted using the constellation PM4, without scrambling and lattice coding, RC, RA, EC, EA are transmitted using the constellation PM8 with coding (R=2/3) and scrambling, and B and D are transmitted with coding, scrambling and at the selected rate (R=2/3) or QAM-32 (R=4/5) or QAM128 (R=6/7).

[0048] List and encode parameters to match connection parameters:

[0049] Coding of connection parameters (RA, RC)

[0050] The first word RA, RC (16 bits) [0051] _SkewTr=$f000;—Request Skew transmitter AFC: Skew: <8-left,>8-right) [0052] _KoefSN=$f000;—s/n estimation or transmitter frequency correction request} [0053] _NonLin=$0800;—Channel nonlinearity found [0054] _CoeFSN=$0400;—s/n transfer sign in first hex digit of SkewTr [0055] _MadeSkewTr=$0200;—Transmitter frequency correction is realized [0056] _Reconnect=$0100;—Parameter exchange completed [0057] _AsimSpeed=$0080;—Asymmetrical speed available [0058] _isRND=$0004;—Random number take place in first hex digit [0059] _hDupl_av=$0020;—hDuplex mode available [0060] _UseV25=$0010;—To use V.25 protocol mandatory [0061] _Wire=$0008;—Wire/Radio h-Duplex mode set [0062] _hDupl=$0040;—h-Duplex mode [0063] _Faza=$0003; {—Connection Phase}

[0064] The second word RA, RC (16 bits) [0065] _9600t=$0080;—9600 transmit available [0066] _9600r=$0040;—9600 receive available [0067] _4800r=$0010;—4800 receive available [0068] _4800t=$0020;—4800 transmit available [0069] _14400t=$0008;—14400 transmit available [0070] _14400r=$0004;—14400 receive available [0071] _14400r=$ff00;—CRC8 of two words

[0072] Description of modem phases:

TABLE-US-00001 FazaMod = 0 The receiver is active, searching for the beginning of the call or answer the call from the correspondent, the transmitter is blocked (FazaRes = 8) FazaMod = 1 The transmitter issues a call (phases 1-4), the receiver is locked (FazaRes = 8) FazaMod = 2 After receiving the call training sequence of the correspondent, the modem transmitter issues a response to the received call (phases 1-3 of the training sequence), and then definitely goes into phase: FazaMod: = 4; FazaRes: = 4 FazaMod = 3 The calling modem receives the first three phases (S, −S, TRN) of the training sequence of the modem that corresponds to FazaMod = 4 Receiving the second training sequence (S, -S, TRN) of the calling modem and issuing a speed selection signal (FazaTr = 4) until the end of receiving the training sequence FazaMod = 5 Issue of the second training sequence by the calling modem (FazaTr = 1-3), the synchronization of the receiver when receiving R2 (FazaRes = 4) FazaMod = 6 Issue of EA and B segments by the called modem and reception of the RC segment by the calling modem FazaMod = 7 Issue of RC, EC, B segments by the calling modem and reception of EA and B segments FazaMod = 8 Data transmission by the called modem and data reception FazaMod = 9 Data transmission by the calling modem and data reception

[0073] Transmitter phase description:

TABLE-US-00002 FazaTr = 0 Bringing the transmitter into readiness and transfer to phase 1 FazaTr = 1 Segment S (transmission of ABAB . . . AB) FazaTr = 2 Segment −S (transmission of CDCD . . . CD) FazaTr = 3 TRN segment (scrambled units) FazaTr =4 Segments R1, R2, R3 (speed selection combinations) FazaTr = 5 Segment E (speed selection end combination) FazaTr = 6 Segment B1 (scrambled and coded units) FazaTr = 7 Data transmission FazaTr = 8 Issue of zeros in the TLC, preparation of the transmission buffer for the issue of samples of the first phase of the transmitter FazaTr = 9 Resetting the transmitter output, continuing to issue previously recorded in the transmitter output buffer FazaTr = 10 Clear the buffer, reset the transmitter into initial condition

[0074] The parameters of the phases of the modem transmitter are presented in the table.

TABLE-US-00003 TABLE Parameters of phases of operation of the modem transmitter Initial Word Initial sample Transmitter Modulation number character number Convolutional phase Designation type (16 bits) number (9600 Hz) coding Scrambling 1 S PM4 0-3 0  0 None None 2 ¦ ¬S PM4 4 32 128 None None 3 TRN PM4  5-36 40 160 None None 4 RA, RC PM8 37 . . . 306 1 224   Present Present 5 EA, EC PM8 n + 38 Present Present 6 B PM8,   n + 39-42 Present Present QAM16-128 7 D PM8, n + 43 Present Present QAM16-128

[0075] Description of receiver phases:

TABLE-US-00004 FazaRes = 0 Bringing the receiver into readiness for transfer to the first phase FazaRes = 1 Search in the input signal of segment S (reception of ABAB . . . AB) FazaRes = 2 Reception of segment -S (reception of CDCD . . . CD) FazaRes = 3 Reception of the TRN segment identifying the frequency and statistical characteristics of the channel FazaRes = 4 Receiving RA or RS segments (receiving a combination of speed selection and common speed selection) FazaRes = 5 Reception of segment EA or EC (reception of a combination of the end of a speed selection) FazaRes = 6 Reception of segment B (scrambled and coded units). Checking the possibility of transition to the data exchange phase FazaRes = 7 Data reception FazaRes = 8 Reception is prohibited, the receiver does not work

[0076] The connection set up protocol according to the claimed method is also illustrated by a state transition diagram (STD), FIG. 4, which indicates the following steps of connection set up: [0077] Beginning—no need to connect. Transition to the “Listening” mode at the time of receipt of connection command; [0078] Listening (Phase 0)—the mode of listening to the channel, during which the occupancy of the channel signal transmission is evaluated. Prolonged listening is equal to T.sub.out (Timeout). After transitioning from the “Listening” mode T.sub.out is approximately 10 ms; [0079] Phase analysis—the mode of receiving a call or answer, in which after the detection of the message header the transition is performed. The received message is recognized as a call or as a response to a call. Accordingly, the transition to the answering mode to the call or the calling mode to the answer, in the case when the answer is not expected; [0080] Standby—the mode of completion of the correspondent modem transmission; [0081] Call transfer (Phase 1)—mode of the call transfer. In this mode, the modem passes in the absence of a signal or immediately after the signal (successfully received or not successfully received) of the correspondent modem, as well as after the timeout waiting for a response to a previous call or a previous answer; [0082] Getting an answer (Phase 3)—the mode of waiting and receiving the correspondent's answer to the call. If the timeout is exceeded or the response contains errors (incorrect CRC, Cyclic redundancy check), then the transition to the call transfer mode. After receiving the expected response, the transition to the phase of evaluation of the parameters of the correspondent contained in the response of the correspondent; [0083] Evaluation of connection parameters. Determination of speed—a mode in which the possibility of establishing a connection on the parameters proposed by the modem of the correspondent is analyzed. If such a possibility is considered not to be realized in the current mode of the channel, then is performed the transition to the transmission phase of the response (Phase 2), in which it is proposed to change the connection parameters (speed reduction, input frequency response of the transmitter, increase the transmission level). If the parameters proposed by the modem of the correspondent can be used to establish a connection, the transfer of consent to the use of the proposed parameters is made; [0084] Transfer of agreed parameters (Phase 5)—the mode of transmission of the agreed connection parameters of the correspondent's modem and the transition to the state of waiting for confirmation of the selected parameters; [0085] Awaiting confirmation—mode of waiting for confirmation of selected parameters. If the selected parameters are not accepted by the correspondent's modem or are not accepted reliably, then the transition to the mode of transmission ending is performed; [0086] Obtaining a training sequence (The result of phase 6)—the mode of reception and verification of the training sequence of a fixed length at a given speed. Upon successful reception, the transition to data transfer is performed. In the presence of errors transition to the mode of transmission ending is performed; [0087] End of transmission—a mode in which the transmission of the sequence of the end of transmission is performed and the transmitter is turned off, and then restart by going to the “Listening” mode (listening to the channel); [0088] Data acquisition (Phase 7)—data reception mode of indefinite duration. Exit from this mode is carried out after receiving the sequence of the end of transmission from the correspondent's modem or receiving a command from the local terminal. If it is impossible to receive reliable information from the correspondent's modem, the transition to the mode of the transmission ending is performed for further restart; [0089] Transmission of response (Phase 2)—the smode of transmission of the answer to the successfully accepted call. The answer contains a set of parameters for establishing a connection, as well as an assessment of the signal quality of the received call. The modem also enters into this mode when the incompatibility of the current connection parameters and channel state estimates is detected; [0090] Waiting for an answer—the mode of waiting for the response of the correspondent's modem. The waiting time is set during the modem configuration process and must be greater than the sum of the propagation delays in the forward and reverse directions; [0091] Receiving parameters (Phase 4)—reception of the proposed connection parameters (speed and the like); [0092] Connection parameters negotiation (Phase 4)—the mode of transmission of the agreed connection parameters. The agreed connection speed can only be equal to or less than the speed offered by the correspondent modem; [0093] Sequence training transmission (Phase 6)—the mode of transmission of the test sequence at selected speed. When receiving a test sequence, the presence of errors is monitored. When errors are detected, the connection is restarted; [0094] Transmission and Receipt (Phase 7)—data status at the selected speed. When receiving the test sequence, the presence of synchronization and errors is monitored. When errors are detected, the connection is restarted.