Method and device for bidirectional transmission using two-wire line

Description: TECHNICAL FIELD [Detailed description of the invention]

The present invention relates to a bidirectional transmission system using a two-wire line, and is particularly suitable for realizing low-speed full-duplex communication and high-speed half-duplex communication using the same transmission medium. Regarding.

[Conventional technology] Conventionally, as a bidirectional transmission system using a two-wire line, an echo canceller method that separates a transmission signal and a reception signal in a transmission / reception terminal and a time-division transmission method that separates a communication time and a reception time are well known. There is. In particular, assuming high-speed data transmission, the time-division transmission method has an advantage that the hardware becomes simpler than the echo canceller method because it does not require a device for echo cancellation. For details on the time-division transmission method, see IEEE, Transaction on Communications, COM-30, No. 9, (1982), pp. 2057 to 2065 (IEEE, Trans. Communications, COM-30, No. 9, It is discussed in detail in (1982) pp2057-2065).

[Problems that the invention tries to solve] The above-mentioned conventional technology is based on the premise that full double communication is performed between the DTE (data terminal equipment) and the switch, but in the state of half double communication in which the transmission direction is only one-way data transmission. , There was a problem that only half of the transmission capacity of the transmission line was used. An object of the present invention is to provide a bidirectional transmission method capable of efficiently utilizing the transmission capacity of a transmission line even when performing half-duplex communication, and particularly low-speed full-duplex communication and high-speed full-duplex communication. The purpose is to efficiently realize half-duplex communication using the same transmission medium.

[Means to solve the problem] In the present invention, in order to achieve the above object, a transmission direction fixed portion is separated into a portion in which the transmission direction is fixedly determined and a portion in which the transmission direction is variable within one cycle (frame) of transmission. Control information that controls the direction of the transmission direction variable unit is transmitted using a part of the signal transmitted in, and the transmission / reception device of the terminal station transmits the frame according to the control information and the state of the data to be transmitted at the terminal station. The transmission direction of the variable direction is controlled.

[Action] In semi-double communication, only one-way data transfer is performed at a certain point in time. Therefore, when there is a communication request from a terminal connected to the transmission / reception device, it is possible to transmit data using the unidirectional transmission unit, but communication of the unidirectional transmission unit between the two transmission / reception devices. It is necessary to decide the direction in advance. In the present invention, bidirectional data transfer is performed in front of the one-way transmission unit in a fixed time manner. Therefore, by exchanging the communication requests of the two transmission / reception devices by using a part of the information, one Direction The communication direction of the transmission line can be controlled for each transmission cycle, and data that takes most of the time in one transmission cycle can be transmitted most efficiently. Further, in terms of the configuration of the device, it can be shared with most of the conventionally known devices by only partially changing the transmission direction control unit of the transmission / reception device, and the economy of the device can be realized.

[Example] FIG. 1 is a diagram illustrating an operation of an embodiment of a bidirectional transmission method using a two-wire line according to the present invention. As shown in (b), two stations A and B are connected by a two-wire line 3, and station A has a data transmission / reception device 1 that connects a telephone or a data terminal device 4 and a line 3, and also a station. B has a data transmission / reception device 2 that connects a terminal 5 such as an exchange and a line 3. In these communication systems, in the present invention, as shown in FIG. 3A, the frame configuration of the signal transmitted by the 2-wire line 3 is from A to B within one frame (hereinafter referred to as transmission cycle). It can be used for transmission in one direction of variable A to B or B to A, and a part where the transmission direction is fixed, such as the transmission unit 6 of the above and the transmission unit 8 of B to A. It is divided into parts 7 and 9. 10,11,12,13 are guard times to prevent signal collision in both directions on the transmission line. In this embodiment, the part where the transmission direction can be changed is divided into two, but as described in other examples, it may be a single portion. In the present invention, the control information for controlling the transmission direction of the portions 7 and 9 having a variable transmission direction is transmitted in the fixed portions 6 and 8. With the above configuration, the transmission cycle is 125 μs, the transmission clock is 2.56 MHz, the number of bits in the variable transmission direction is 192 bits, and the number of bits in the fixed transmission direction is 26 in each direction. When 4 bits of the signal for controlling the transmission direction of the variable direction transmission unit are assigned, (1) 144Kbps dual-sided Dane transmission channel (2) 32Kbps directional variable transmission section directional control channel (3) Three channels of 1.536 Mbps variable direction transmission can be realized on a 2-wire transmission line. In order to realize the above three channels, it is necessary to transmit 244 bits of data in 125 μs, which requires 95.4 μs, so the remaining 29.6 μs is the guard time (10,11,12,13). Can be assigned. An example of how to switch the transmission direction of the above method will be described with reference to FIG. 14 represents low-speed data that requires real-time property and interactivity such as voice, and 15 represents high-speed data that does not require much real-time property and interactivity such as binary data. When one data transmission / reception device 1 and the other data transmission / reception device 2 communicate with each other, basically, as shown in Fig. 2 (a), low-speed data is first transmitted from A to B, then high-speed data is transmitted, and then high-speed data is transmitted. The transmission of low-speed data and high-speed data from B to A is repeated. When station A has high-speed data to be transmitted but station B does not have high-speed data to be transmitted, as shown in Fig. 2 (b), low-speed data and high-speed data are transmitted from A to B, and B to A. After transmitting the low-speed data to, A detects that the high-speed data is not sent from B, and conversely transmits the high-speed data from A to B. By repeating this process, low-speed data is transmitted in both directions of A and B, while high-speed data is transmitted in one direction from A to B. When A does not have the high-speed data that it wants to transmit and B has the high-speed data that it wants to transmit, the exact opposite is done. When both stations A and B do not have the high-speed data that they want to transmit, as shown in Fig. 2 (c), first send low-speed data from A to B, and then B does not send high-speed data from A. Detects and sends a dummy bit (16) from B to A. Then, after transmitting low-speed data from B to A, A detects that high-speed data will not be sent from B in the future, and sends a dummy bit 16 from A to B. Dummy bit 16 has no meaning as information, but sends, for example, an all "0" pattern to perform timing extraction. FIG. 3 shows the configuration of an embodiment of the data transmission / reception devices 1 and 2. Input signals from the low-speed port and high-speed port are stored in buffers 103 and 104 via interfaces 101 and 102, respectively. The transmission data is created by the transmission data generation unit 107 according to the instruction of the direction control unit 108 that executes the above-mentioned direction control algorithm. The encoder 113 converts the transmission data into a transmission line code and outputs the transmission data to the 2-wire transmission line 117 via the transformer 116. On the other hand, the received signal from the two-wire line 117 is input to the equalizer 114 by the switch 115 controlled by the direction control unit 108 for the time for receiving the data. The equalizer output is converted from the transmission line code into an NRZ signal by the decoder 112, separated into a low-speed port signal and a high-speed port signal (109), via buffers (105), 106, and interfaces 101, 102, respectively. Output to the port. The equalizer output is also supplied to the timing extraction unit 111, and the clock signal used for the reception operation is extracted. The frame synchronization extraction unit 110 establishes frame synchronization from the code conversion unit output, and supplies frame synchronization information to the direction control unit 108. FIG. 4 shows an embodiment of the signal configuration. 2B + D channel is assigned as low-speed data, and H11 channel is assigned as high-speed data. As shown in (a), the low-speed data is F1 flag pattern "0110" (17) for frame synchronization, 4 bits, 8 bits each for B channel data (18, 19), and 2 for D channel data. Bits (20) And the direction control bit (21) that notifies whether to continuously send high-speed data is 4 bits. Set 1111 if you want to send high-speed data continuously, and set 0000 if you do not want to send it continuously. The frame configuration of high-speed data sends H11 channel data (23) 96 bits following the F2 flag pattern (22) 4 bits as shown in (b). Figure (c) shows the case where high-speed data (b) is sent after low-speed data (a). Fig. 5 shows the algorithm for controlling the direction in the signal configuration of Fig. 4. First, when A transmits data, it sends 4 bits of the F1 flag for frame synchronization (26), and then sends a total of 18 bits of 2B + D data (27). Furthermore, it is determined whether or not there is a transmission request for H11 data (28), and if there is a transmission request, a "1111" pattern is transmitted as a direction control signal (29), followed by transmission of 4 bits of the F2 flag and 96 bits of H11 data. (30,31). On the other hand, if there is no H11 data transmission request, the reception state is entered after the direction control bit "0000" pattern is transmitted (32). Receive the first 4 bits of the signal transmitted from B (32) and compare it with the F2 flag pattern (34). If it matches the F2 flag pattern, the subsequent 96-bit signal is received as H11 data (35). If there is a discrepancy, the following 96 bits of the signal are judged to be dummy data (36). A then receives the F1 flag sent by B (37). Subsequently, 18 bits of 2B + D data are received (38), and further, a direction control bit is received (39). If the direction control bit is determined and (40) is "1111", the F2 flag 4 bits and the H11 data 96 bits that are continuously sent are received (41,42). If the direction control bit is "0000", A determines whether there is a request to transmit H11 data (43). If there is a transmission request, the F2 flag 4 bits and then the H11 data 96 bits are transmitted (44,45). If there is no request to send H11 data, 100 bits of all 0 patterns are sent as a dummy (46). This completes one transmission cycle. FIG. 6 shows the configuration of an embodiment of the device for realizing the above-mentioned direction control method. FIG. 6 shows the insides of the transmission pattern generation unit 107, the direction control unit 108, and the reception pattern separation unit 109 of FIG. The operation of this circuit will be described in the order shown in the flowchart of FIG. First, the data of the 2B + D channel is stored in the low-speed data buffer 103, and the data of the H11 channel is stored in the high-speed data channel buffer 104. The 2B + D data is cut out every 18 bits and transferred to the shift register 120, and the H11 data is cut out every 96 bits and transferred to the shift register 121. The shift register 120 has 22 bits, and 2B + D data is stored in the left 18 bits and the F1 flag "1001" is stored in the right 4 bits. Similarly, the shift register 121 has 100 bits, H11 data is stored in the left 96 bits, and the F2 flag "0110" is stored in the right 4 bits. Further, the ROM 122 stores the transmission status flags "1111" and "0000" and the all-zero pattern to be sent as a dummy bit. The frame synchronization extraction unit 110 in Fig. 3 extracts the frame synchronization signal at 8kHz intervals using the F1 flag of the received signal, so this is delayed by 62.5 μsec by the delay device 139 in Fig. 6 and used as the transmission timing signal. To do. The transmit timing signal activates the flip-flop 125, the line 160 goes to a high (henceforth H) level while the timer 126 counts 22 bits of time, the selector 123 selects the shift register 120, and F1 Flags and 2B + D data are sent in sequence. Then, the flip-flop 128 is activated and the line 161 becomes H level. Meanwhile, the flip-flop 136 is also activated at the same time to bring line 162 to a voltage equal to the logic level of line 165. Line 165 exits the high-speed data buffer 104 and takes H level if there is a request to send H11 data, and L level if there is no H11 data transmission request. Therefore, if there is a request to transmit H11 data, line 161 will be at H level, line 162 will also be at H level, and selector 123 will select and transmit the "1111" pattern of ROM 122, while if there is no request to transmit H11 data, it will be transmitted. , Line 161 is H level, line 162 is L level, and selector 123 selects and transmits the "0000" pattern in ROM 122. If there is no request to send H11 data, this completes the transmission. When there is a request to transmit H11 data, the flip-flop 132 is further activated, the line 163 becomes the H level, and the selector 123 selects the shift register 121. This state continues while timer 133 counts 100 clocks. When the transmission is completed, all of the lines 160,161,162,163,164 are at the L level, so the gate 124 detects the end of the transmission and switches the switch 115 to the receiving side. On the receiving side, the selector 152 normally selects the shift register 150, and the gates 148 and 149 detect the F1 flag and the F2 flag, respectively. When the F1 flag pattern "1001" is received, the flip-flop 141 is activated after confirming at the gate 140 that the timing matches the already extracted frame synchronization signal. The timer 142 keeps the line 166 at H level for 187 clocks, and the selector 152 selects the slow data buffer 105 to send 2B + D data. The flip-flop 143 is then activated, the timer 144 keeps the line 167 at H level for four clocks, and the selector 152 selects the shift register 151. Here, the direction control bit is determined, but a majority circuit that outputs the H level is used if there are many signals of 1 out of 4 bits so that the correct determination can be made even if an error of 1 bit occurs during transmission. Here, when H11 data is subsequently sent, an H level signal is output, and when the other party's transmission is completed, an L level signal is output. After receiving the directional control bit, the flip-flop 143 is reset and the selector selects the shift register 150 again. If the F2 flag is detected here, the flip-flop 145 is activated, line 168 is kept at H level while timer 146 counts 96 clocks, selector 152 selects fast data buffer 106 and receives H11 data. To do. On the other hand, when the received direction control bit is determined to be "0000", the line 169 becomes the L level. If there is H11 data to be transmitted to the other party here, line 165 is at H level, flip-flop 136 is activated, and H11 is transmitted. If there is no H11 data to send to the other party, line 165 is L level, gate 138 outputs H level, flip-flop 134 is activated, line 164 is H level, and selector 123 is a dummy pattern in ROM 122, that is, all zero. Select a pattern. This continues while timer 135 counts 100 clocks. In this way, the operation of the transmission / reception 1 transmission cycle is completed. In this embodiment, the data transmission / reception device required for the PBX side and the terminal side can be realized by a common algorithm and circuit. FIG. 7 shows a signal configuration in one transmission cycle in another embodiment of the present invention. In this embodiment, one transmission cycle is one of two parts 6 and 7 that perform fixed transmission from A to B and B to A, and either A to B or B to A in each cycle. It is divided into a single part 9 that carries out transmission. More specifically, one transmission cycle is 125 μs (8 kHz), and the transmission speed is 2.04 MHz. Therefore, 256 bits can be arranged in the time domain of 125 μs. Of the 256 bits, 16 bits are in each of the two parts 6 and 7 where the transmission direction is fixed, 184 bits are in the one-way transmission part 9, and the remaining 40 bits (256-184-2 × 16) are Allotted to card times 10,11,12. Each of the 16 bits of the divisions 6 and 7 includes 4 bits of a frame synchronization signal, 2 bits of a signaling signal, and 2 bits of a transmission direction control signal of the one-way transmission unit 9. Depending on the above signal configuration (a) 64Kbps bidirectional data transmission channel (b) 16Kbps signaling channel (can be used as an ISDN D channel when the DTE104 side becomes an exchange) (c) 16Kbps one-way transmission channel for transmission direction control (d) 1.472 Mbps semi-duplex communication channel 4 channels can be realized on a 2-wire transmission line. As an embodiment of the transmission direction control method of the one-way transmission unit, a method in which one data transmission / reception device (A) serves as a master station and the other data transmission / reception device (B) serves as a slave station to control the transmission direction will be described. .. 2 bits of transmission direction control channel for direction control (abbreviated as S, T, S bit transmitted from A to B is S_{A B}, S and T bits transmitted from B to A are S respectively_{B A}, T_{B A}To) is used. T_{A B}Is not used. S_{A B}= '1' indicates that the one-way transmission part 9 is used for data transmission from A to B or B to A, T_{B A}= '1' indicates that there is a data transfer request from B to A. The operation of the data transmission / reception device A is as follows. (a) T before one transmission cycle_{B A}= '0' and there is a data transmission request to B: S_{A B}= '1' and use the one-way transmission line for data transmission from A to B. (b) T before one transmission cycle_{B A}= '0' and no data transmission request to B: S_{A B}= '0'. S_{B A}If = '1', the data from B is received. (c) T before one transmission cycle_{B A}= '1', and there is a data transmission request to B: When there is a data transfer request in both directions, determine the transmission direction so that it is opposite to the previous data transfer direction. S if the transfer direction is A B_{A B}Transfer data to B as = '1'. Conversely, if the transmission direction is B A, then S_{A B}Receive data from B with = '0'. (d) T before one transmission cycle_{B A}= '1' and no data transfer request to B: S_{A B}Receive data from B with = '0'. On the other hand, the data transmission / reception device B operates as follows. (a) If there is no data transfer request to A: S_{A B}If = '1', the data from A is received. (b) If there is a data transfer request to A: S_{A B}If = '0', S_{B A}Transfer data to A with = '1. S_{A B}Set = '1' and receive the data from A. Figure 8 shows an example of communication using the communication direction control method described above. In the figure, S_{A B}, S_{B A}, T_{B A}And 1.472 Mbps communication channel data transfer direction is shown. Fig. 8 (a) shows the case where there is only a communication request from B to A. S_{A B}Since = 0, it is possible to continuously transfer data from B to A. Similarly, Fig. 8 (b) shows the case where there is only a communication request from A to B. FIG. 8 (c) shows a case where there is a communication request in both directions of A B and B A, and the communication direction of the 1.472 Mbps communication channel alternately becomes A B, B A for each frame. As shown in FIG. 8, according to this embodiment, continuous transfer of 1.472 Mbps is possible when performing half-duplex communication, and even when applied to full-duplex communication, all of 0.736 Mbps is possible. Double communication is possible without hardware changes. Moreover, if the transmission direction is fixed in only one direction, one-way communication of 1.472 Mbps can be realized. Since the configuration of the transmitter / receiver when the method shown in FIG. 8 is carried out can be configured in almost the same manner as the configurations shown in FIGS. 3 and 6, detailed description thereof will be omitted. The specific configuration naturally differs depending on the change in the transmission speed and the number of bits. Also, since the part that transmits in one direction (9 in Fig. 7) is one in one transmission cycle and is after the two fixed parts 6 and 7, the logical configuration of the logic circuit of the direction control unit 108 in Fig. 3 is Different from the original in Figure 6. The table below shows the logic table for the operation of the above logic circuit.<img file="JP2718673B2_D0001.tif" /> Here S'_{B A}Is a signal_{A B}Represents a signal delayed by one cycle. X can be any signal bit.

[Effect of the invention] According to the present invention, high-speed half-duplex communication can be realized using a two-wire line, and it can also be applied to full-duplex communication without changing hardware. Therefore, a two-wire line is used. It is effective in improving the data transmission speed, making the data transmission / reception device economical, and simplifying it. In the embodiment showing the operation shown in FIG. 1, since the transmission / reception device of the two terminals connected via the two-wire line can be configured exactly the same, it has the effect of reducing the manufacturing cost, and further, in the terminal device. , Low-speed data must be sent, but when high-speed data does not exist, if a dummy signal is sent, it has the effect of correctly extracting the timing signal.

[Simple explanation of drawings]

FIG. 1 is a drawing showing the operation of an embodiment of the bidirectional transmission direction according to the present invention, FIG. 2 is a drawing showing the operation of FIG. 1 in chronological order, and FIG. 3 is a bidirectional transmission direction according to the present invention. FIG. 6 is a block diagram of an embodiment of a transmission / reception device implemented in the above, FIG. 4 is a signal configuration diagram of an embodiment of the present invention, FIG. 5 is a flowchart showing a direction control algorithm of an embodiment of the present invention, and FIG. Is a circuit diagram of an embodiment of a main part of FIG. 3, FIG. 7 is a drawing illustrating the operation of another embodiment of the bidirectional transmission method according to the present invention, and FIG. 8 is a diagram of the embodiment of FIG. It is a drawing which showed the operation in chronological order. 1 ...... Data transmission / reception device A, 2 ...... Data transmission / reception device B, 3 ...... 2-wire transmission line, 4 ...... DTE (A), 5DTE (B), 6 ...... A to B transmission unit, 8 ...... B to A transmission unit, 7, 9 ...... Variable transmission direction unit, 10, 11,12,13 ...... Guard time, 14 ...... Low speed data, 15 ...... High speed data, 16 ...... Dummy bit, 17. .... .F1 flag, 18,19 ...... B channel data, 20 ...... D channel data, 21 ...... direction control bit, 22 ...... F2 flag, 23 ...... H11 channel data, 101,102 ...... interface, 103,105 ...... low speed data buffer, 104,106 ...... high speed data buffer, 107 ...... transmission pattern Generation unit, 108 ...... Direction control unit, 109 ...... Reception pattern separation unit, 110 ...... Frame synchronization extraction unit, 111 ...... Timing extraction unit, 112 ...... Decoder, 113 ...... Encoder, 114 ...... Equalizer, 115 ...... Changeover switch, 116 ...... Transformer, 117 ...... 2-wire transmission line.