JPS6223631A - Data transmission equipment - Google Patents

Abstract

PURPOSE:To avoid disturbance due to far-end crosstalk by bringing the reception level of a master station into nearly the same level among slave stations regardless of each core wire length when the master station and plural slave stations are connected by exclusive core wires in the same cable. CONSTITUTION:A slave station uses a level detection means 49 so as to detect at which level range set (depending on the core wire length between each slave station and the master station) the reception level of the 1st training signal from the master station exists, a transmission gain of a transmission amplifier 50 is set accordingly and a pulse train signal having a period representing the said gain is sent from a coincidence decision section 51, a changeover circuit 54 and pulse train signal generating circuits 56-58. The master station uses a pulse period detection means 30 to detect the said period and discriminates the transmission gain of the slave station accordingly thereby deciding the gain of a reception amplifier 27 at each slave station. Further, the 2nd training signal including the gain information is sent to the slave station. When the coincidence between the said gain information and gain information set by the slave station is detected, the slave station sends a signal in response to the master station. The master station discriminates that a pull-in end detection section 29 establishes the channel.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a data transmission device comprising a master station and a plurality of slave stations connected to the master station by respective dedicated cables. This invention relates to technology for reducing far-end crosstalk during transmission.

(Prior Art) FIG. 6 is an overall configuration diagram of a data transmission device to which the present invention is applied. This data transmission device includes a master station 60 and a plurality of slave stations (
In the illustrated example, there are three) 61a.

61b and 61e, each slave station 61a.

61b and 61e are dedicated cables 62a, respectively.

The terminals 62b and 62e are connected to the master station 60. and,
The dedicated cables 62a, 62b, and 62C are not laid along independent wiring routes, but are laid as one multicore cable 63 to increase installation efficiency, and are placed near each slave station. Each dedicated cable is distributed and connected.

In this type of data transmission device, when communicating between the master station and each slave station, the transmission information is converted into a code consisting of a binary signal, and the code is further converted into a pulse train with a pulse waveform suitable for transmission. and send it to the cable. However, since cables have frequency characteristics in transmission loss, the pulse train that reaches the receiving end has a distorted waveform and its reception level also decreases. It includes an equalizer for obtaining a received waveform that is optimal for correctly identifying codes, and an amplifier that adjusts the input level of the equalizer to an appropriate level.

(Problem to be Solved by the Invention) However, in this type of transmission device, the master station 60 is connected to each slave station 61.
a, 61b2, 61e, the master station 6
Since each transmission level of 0 is the same level, each slave station 61
Cables 62a, 61b, and 61e can be received normally without crosstalk problems, but when the master station 60 receives them, the cable lengths of the dedicated cables 62a, 62b, and 62c are different, which means that the reception level is different. and each dedicated cable 62a,
Since one end of the receivers 62b and 62c is tied together at the master station and placed close to each other, far-end crosstalk occurs, making normal reception difficult.

That is, when the master station 60 receives signals, the signal level from the closest slave station 61a is the highest, and the signal level decreases as the distance increases from slave stations 61a, 61b, and 61c. - Therefore, for example, as shown in the figure, far-end crosstalk 63. 64 occurs, and the level of crosstalk from the high-level cable 62a to the low-level cable 62e is particularly large, deteriorating the S/N ratio of the signal from the slave station 61c.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide data transmission that can avoid interference due to far-end crosstalk by ensuring that the receiving level of the master station is approximately the same level between each slave station regardless of the difference in cable length. The goal is to provide equipment.

(Means for Solving the Problems) In order to achieve the above object, a data transmission device according to the present invention includes a master station and a plurality of slave stations connected to the master station by respective dedicated cables. In the data transmission device, the communication control unit provided by the master station for each of the slave stations is a transmitting unit that transmits data to the slave stations so that each transmission level at the transmission end to each of the dedicated cables is the same. , a receiving section that receives transmission data from the slave station, and a first pulse pattern that includes a predetermined pulse pattern for requesting connection of a communication path to the slave station.
a first transmitting a training signal of
a transmitting means, a pulse period detecting means for detecting a pulse period of a pulse train signal with a predetermined period received by the receiving section as a response to the first training signal, gain determining means for determining a transmission gain; second transmitting means for transmitting a second training signal including the determined gain information as a response to the pulse train signal via the transmitter; and the second training signal. When the content of the response transmission received by the receiving unit as a response to the request is a training signal requesting the master station to connect a communication channel, a third training signal including training completion information for controlling communication channel establishment is transmitted. The communication control unit, which includes a training end processing means for transmitting data via the transmitting unit and performs a training end process in the master station, and is controlled by each of the slave stations, receives transmission data from the master station. a receiving section, a transmitting section having a transmission amplifier with a changeable transmission gain, and which level range of a plurality of preset level ranges the reception level of the first training signal received by the receiving section is in. level detection means for detecting the level range; gain setting means for setting the transmission gain of the transmission amplifier according to the detected level range; a first transmitting means that transmits via the transmitting section in which the gain is set as a response to a gain value indicated by gain information included in the second training signal received by the receiving section and the set gain value; and a judgment result of the judgment means, in the case of a mismatch, a pulse train signal of the predetermined pulse period, and in the case of a match, a predetermined pulse pattern for requesting connection of a communication path. a second transmitting means for transmitting the training signal as a response to the second training signal via the transmitting section whose gain is set respectively; and training included in the third training signal received by the receiving section. The present invention is characterized in that it includes a training end processing means for performing training end processing in its own station based on the end information.

(effect) Hereinafter, the operation of the device of the present invention having the above configuration will be explained.

The master station transmits the first training signal from the first transmitting means to the slave station that requires connection of the communication path via the transmitting section. The slave station uses a level detection means to detect in which level range the reception level of the first training signal falls within a plurality of preset level ranges, and transmits the own station using a gain setting means according to the detected level range. A transmission gain of the amplifier is set, and a pulse train signal with a predetermined pulse period indicating the predetermined gain that has been set is also transmitted from the first transmitting means through the transmitter as a response to the first training signal. The transmission level at this time is based on the set transmission gain.

Next, the master station detects the pulse period of the received pulse train signal using the pulse period detection means, determines the transmission gain of the core slave station according to the detected pulse period using the gain determination means, and performs a second training including the determined gain information. A signal is transmitted from the second transmitting means via the transmitting section. On the other hand, the slave station uses a stabbing means to determine whether or not the gain value indicated by the gain information included in the second training signal matches the set gain value, and if they do not match, the pulse train signal of the predetermined pulse period is sent again. is transmitted from the second transmitting means via the transmitting section as a response to the second training signal. On the other hand, the master station determines the transmission gain again and transmits the gain information to the slave station. If they match, the training signal is transmitted from the second transmitting means via the transmitting section as a response to the second training signal.

On the other hand, in the master station, the determination means determines that the training for establishing a communication channel has been completed, and the training completion processing means transmits a third training signal containing training completion information to the slave station. In addition, the training end process is performed for the own station, that is, the transmission and reception of general data becomes possible. On the other hand, in the slave station, upon receiving the third training signal, the training end processing means performs the training end T process in its own station,
It is possible to send and receive general data in the same way as the master station.

Here, the transmission gain set according to the reception level on the slave station side is set so that the reception level of the master station is approximately the same for each slave station, so each reception level at the master station The difference will be extremely small. Therefore, even if one end of each dedicated cable is bundled and placed close to each other on the master station side, the occurrence of far-end crosstalk can be significantly reduced.

<Embodiment> FIG. 1 is a diagram showing the overall configuration of a data transmission device according to an embodiment of the present invention.

As in the conventional example, the overall configuration of this data transmission device consists of a master station], a plurality of slave stations (three in the illustrated example) 2a distributed at appropriate distances 1- from the master station 1; Consisting of 2b and 2c, each slave station 2a, 2b and 2c
are the master stations using dedicated cables 3a, 3b and 3c, respectively]
, and each dedicated cable 3a, 3b
And 3<] is one multicore cable 4 and 1. The terminals are laid down and distributed and connected near each slave station 2a, 2b, and 2C.

As shown in FIG. 2, the master station 1 includes a center unit W2 which manages general data to be transmitted and received for each slave station, and a center unit W2 which is provided for each slave station and controls the establishment of a communication path at the time of starting communication. and a communication control section (only one unit is shown) 22 that controls the transmission and reception of data. You can connect via the same 24.

The communication control unit 22 includes an input terminal 25 to which an uplink cable (not shown) is connected, and an output terminal 26 to which a downlink cable (not shown) is connected. Between the input terminal 25 and the terminal 23, a receiving amplifier 27 and an equalizer 28 as a receiving section are arranged in order from the input terminal 25 (Ill).The receiving amplifier 27 is a gain variable type, and in the initial state, the gain is set to the maximum. The pulse wave applied to the input terminal 25 is amplified to an appropriate level by the receiving amplifier 27 and is set to a predetermined gain as described later in the process of establishing a communication path.
8 is output.

The equalizer 28 makes the received waveform optimal for identifying the input pulse wave without error (this is called "drawing").
It is output to the center device 21 via the terminal 23. A pull-in completion detector 29 detects whether the equalizer 28 has completed the pull-in, that is, whether the intersymbol interference value has fallen within a predetermined value. The output of this pull-in completion detection section 29 is input to the switching circuit 31 and the pull-in completion information insertion section 33, respectively. Further, a pulse period detection section 30 is provided on the output side of the equalizer 28. This pulse period detecting section 30 detects the pulse period of the pulse train signal transmitted by the slave station as described later in the process of establishing a communication path, and transmits gain information corresponding to the detected pulse period to the receiving amplifier 27 and the gain information inserting section 3.
In other words, the pulse period detecting section includes both a pulse period detecting means and a gain determining means.

Further, between the terminal 24 and the output terminal 26, the switching circuit 31, the gain information insertion section 32, the pull-in completion information insertion section 33, and the transmission amplifier 34 in the transmission section 17 are arranged in order from the terminal 24 side. ing. General data sent from the center device 21 via the terminal 24 and a training signal output from the I/learning signal generation circuit 35 are input to the switching circuit 31, respectively. Although not shown, the l-laning signal consists of a pulse pattern specially devised to draw in the equalizer of the partner slave station in order to establish a communication path. It is well known that various pulse patterns of the 1.l/-ning signal have been proposed. The switching circuit 31 switches between the training signal and the general data according to the output state of the pull-in completion detection section 29 and outputs the signal to the gain information insertion section 32 . In other words, the switching circuit 31 outputs a training signal assuming that the communication channel establishment process is still in progress until the pull-in completion detection section 29 detects the completion of the pull-in, and after the detection, outputs the training signal as a general signal from the center device 21 assuming that the communication path establishment process has ended. Enable data transmission.

The gain information insertion section 32 inserts the gain information from the pulse period detection section 30 into the 1-I/-ning signal at a predetermined gain information bit position, and outputs it to the pull-in completion insertion section 33. In this embodiment, the gain information includes 3
Therefore, for example, 2 bits are prepared as gain information bits, and one gain information is displayed by the logic state of 2 bits. The pull-in completion insertion section 33 inserts the pull-in completion information from the pull-in completion detection section 29 into the training signal at a predetermined completion information bit position, and outputs it to the transmission amplifier 34.

The transmission amplifier 34 amplifies the training signal or general data to a predetermined level and sends it to a dedicated cable (not shown) via the output terminal 26. At this time, the output level at the output terminal 26 is set to be approximately the same level for each slave station.

On the other hand, as shown in FIG. 3, each slave station includes a terminal device 41 that manages general data to be transmitted and received, and a communication control unit 42 that controls the establishment of a communication path at the start of communication and controls the transmission and reception of general data. The terminal device 41 and the communication control section 42 are connected via terminals 43 and 44.

The communication control unit 42 includes an input terminal 4.5 to which a downlink cable (not shown) is connected, and an output terminal 46 to which an uplink cable (not shown) is connected. Between the input terminal 45 and the terminal 43, a receiving amplifier 47 and a receiver 48 as a receiving section are provided in order from the input terminal 45 side.

The reception amplifier 47 has a reception gain fixed to a constant value, and amplifies the pulse wave applied to the input terminal 45 to an appropriate level and outputs it to the flower vase 48.

The equalizer 48 has the same function as the equalizer 28, and transmits the received waveform most suitable for identification to the terminal device 4 via the terminal 43.
Output to 1.

A receiving level division detecting section 49 serving as a level detecting means and a gain setting means is connected to the input terminal 45 separately from the receiving amplifier 47 □. The reception level division detection section 49 detects which of the preset level divisions the reception level corresponds to, and outputs gain information corresponding to the detected level division to the transmission amplifier 50 and the coincidence determination section 51 as a determination means. do. In this embodiment, three types of reception level classifications are provided, and each level classification corresponds to the three types of gain information (details will be described later).

In addition, the output of the equal flower vase 48 is inputted to a gain information detection section 52 and a pull-in completion information detection section 53, respectively. extracted from the output signal of
This is output to the coincidence determination section 51. Match determination unit 51
determines whether the gain information from this gain information detection section 52 and the gain information from the reception level division detection section 49 match or do not match, and outputs the determination result to the switching circuit 54, and also includes a pull-in completion information detection section. 53 extracts the pull-in completion information inserted into the training signal by the pull-in completion information inserting section 33 from the output signal of the flower vase 48, and outputs this to the switching circuit 54.

The switching circuit 54 and the transmission amplifier 50 are provided between the terminal 44 and the output terminal 46 in this order.

The switching circuit 54 receives general data sent from the terminal device 41 via the terminal 44 and a training signal generation circuit 55.
training signals and three pulse train signal generation circuits 56. Three types of pulse train signals (FIG. 4) from 57 and 58 are respectively inputted, and these input signals are switched and controlled in response to output signals from the coincidence determination section 51 and the pull-in completion information detection section 53. It is output to the transmission amplifier 50.

FIG. 4 shows the three types of pulse train signals, and in FIG. 4(A), the pulse train signal generating circuit 56 generates the pulse train signals, and the pulse period thereof is TI. In the figure (B), the pulse train signal generating circuit 57 generates a pulse train, and the pulse period thereof is T2.

In addition, in FIG. 5C, the pulse train signal generating circuit 58 generates a pulse train, and the pulse period thereof is T3.

These pulse periods display the three types of gain information, and any one of the pulse train signals is selected according to the gain information output from the reception level classification detection section 49. In other words, the pulse period detection section 3
0 detects one of these three pulse periods and determines the gain information it displays.

Note that the training signal generated by the training signal generation circuit 55 is the same as that in the master station 1. The transmission amplifier 50 is of a variable gain type, and is set to a predetermined gain value according to the gain information from the reception level division detection section 49, and amplifies the output from the switching circuit 54 to the set gain and outputs it to the output terminal 46. Send to.

Next, each communication control 22 and 42 configured as described above
The control operation for establishing a communication path performed by the controller will be explained with reference to FIG. First, the master station 1 transmits a training signal at a normal transmission level to a predetermined slave station (in whole or in part) and issues a connection request for 5 communication channels (step 100). In other words, the switching circuit 31 detects the completion of the pull-in. Upon receiving the control signal from section 29, the output of training signal generating circuit 35 is selected, and gain information inserting section 32. It is output to the transmission amplifier 34 via the pull-in completion information insertion section 33.

At this time, the gain information inserting section 32 and the pull-in completion information inserting section 33 do nothing to the training signal, and simply allow it to pass through. Therefore, the training signal generating circuit 35° switching circuit 31 and the pull-in completion detecting section 29 collectively constitute a first transmitting means.

When the slave station receives the training signal (step 20
0), retraction operation in the equalizer 48 (step 21
0) and the operation of detecting the reception level classification in the reception level classification detection section 49 (step 220) are performed in parallel. Regarding reception level classification, in this embodiment, master station 1
The reception level of the remote station 2c furthest from the station is set as the reference level, and this reception level classification 1 is set.
The reception level whose increment is within a dB is defined as reception level classification 2, and the increment from reception level classification 1 is within a dB.
The above reception level is set as reception level classification 3.

That is, the reception level division detection section 49 detects that the reception level is
It determines which reception level category the species belongs to and detects that level category.

Then, when the drawing-in operation of the equalizer 48 is completed, the reception level division detection section 49 outputs the detected reception level division information to the transmission amplifier 50 and the coincidence determination section 51 (step 210). That is, the reception level division detection section 49 has the functions of a level detection means and a gain information setting means for outputting gain information of the transmission amplifier corresponding to the level division detected by the level detection means.

The transmission amplifier 50 receives the gain information and sets the reception level classification to the normal level that the farthest slave station 2C transmits to the master station when the reception level classification is 1, and the normal level when the reception level classification is 2. to the A level, which is reduced by A dB (
If the reception level is class 3, the transmission gain (corresponding to the slave station 2a) is set to the B level (corresponding to the slave station 2a), which is the normal l/bell reduced by B dB.

On the other hand, since there is no input from the gain information detection section 52, the coincidence determination section 51 determines whether
When the reception level is classification 1, the pulse and pulse train signal generation circuit 56
A switching circuit sends a control signal to the effect that the output of the pulse train signal generating circuit 57 should be selected and output when the reception level is classified as 2, and the output of the pulse train signal generating circuit 58 is selected and output when the reception level is classified as 3. 54. Switching circuit 54
Since there is no input from the pull-in completion information detection section 53, a pulse train signal with a designated pulse period is output to the transmission amplifier 50 in accordance with the control signal instruction from the coincidence determination section 51. As a result, the master station receives a pulse period of T1 as a response to the training signal. T2. The pulse train signal which is one of T3 is transmitted at the corresponding transmission level (step 230), therefore, the coincidence determination unit 5
1. and three pulse train signal generation circuits 56. 57, 58, and the switching circuit 54 collectively constitute a first transmitting means.

The master station 1 receives the pulse train signal in step 11.
0), that is, when the training signal in step 260 is not received from the slave station as a response to the training signal transmission from the master station, the pulse period detection section 30 detects the pulse period of the pulse train signal, and also detects the pulse period of the pulse train signal. The receiving gain is determined according to the pulse period (step 120), and the receiving gain of the receiving amplifier 27, which is initially set to the maximum value, is reset for each slave station.

As a result, the reception gain of the reception amplifier 27 is equal to the pulse period T1.
For the slave station (2C) that sent a pulse train signal of
Further, for the slave stations (2a) that have transmitted the pulse period T3, the respective gain is set to "normal gain +B dB". The gain information set in this way is output to the gain information insertion section 32.

Since the switching circuit 31 does not receive the detection signal from the pull-in completion detecting section 29, the output of the training signal generating circuit 35 is selected and sent to the gain information inserting section 32. As a result, gain information is added to the training signal as described above, and the training signal is transmitted to the slave station (step 130). Therefore, the pulse period detection section 30 has the functions of a pulse period detection means and a gain determination means. In addition, the gain information insertion unit 32
together with the training signal generating circuit 35, the switching circuit 31, and the pull-in completion detecting section 29 constitute a second transmitting means as a whole.

When the slave station receives a training signal including gain information, the gain information detection unit 52 extracts the gain information from the output of the equalizer 48 (step 240), and the match determination unit 51 extracts the gain information from the output of the equalizer 48.
Output to. The match determining unit 51 determines whether this gain information matches the gain information from the reception level classification detecting unit 49 (step 250). If the answer is NO, the process returns to step 230 and transmits the pulse train again. If the result is affirmative (YES), a control signal is sent to the switching circuit 54 instructing it to select the output of the training signal generating circuit 55. Output. As a result, the training signal is transmitted to the master station 1 with a predetermined transmission gain (
Step 260), therefore, the coincidence determination section 51, the training signal generation circuit 55, and the switching circuit 54 as a whole are
It constitutes a transmission means.

When the master station 1 receives the training signal (step 140), it waits for the drawing operation of the equalizer 28 to be completed (step 150), and the drawing completion detection unit 29 detects the drawing operation of the equalizer 28. When completion is detected, the retraction completion information is first inserted into the retraction completion information insertion section 33.
Output to.

As a result, the pull-in completion information is added to the training signal as described above and transmitted to the slave station (step 160), and then the pull-in completion detecting section 29 outputs the pull-in completion information to the switching circuit 31. Switching circuit 3
1 performs a switching connection operation to selectively output the general data sent from the center device 21 via the terminal 24 upon receiving the pull-in completion information, and in step 170), the communication channel establishment control process on the master station 1 side is completed. Therefore, the pull-in completion detection section 29, the pull-in completion information insertion section 33, the training signal generation circuit 35, and the switching circuit 31 collectively constitute training completion processing means.

On the other hand, when the slave station receives the training signal, the pull-in completion information detection section 53 extracts the pull-in completion information from the output of the equalizer 48 (step 270), and outputs it to the switching circuit 54. Upon receiving the pull-in completion information, the switching circuit 54 performs a switching connection operation to selectively output general data sent from the terminal device 41 via the terminal 44 (step 280), and ends the communication path establishment control process on the slave station side. . Therefore, the pull-in completion information detection section 53 and the switching circuit 54 collectively constitute a training completion processing means.

By the above procedure, the farthest child station 2C with the longest cable length is
transmits at the normal level, the nearest slave station 2a with the shortest cable length transmits at a level reduced by B dB from the normal level, and slave station 2b, whose cable length is between the two, transmits from the normal level. Transmission will be performed at a level reduced by AdB. As a result, the level difference between the reception levels at the input terminals 25 of the communication control units of the master station 1 and 22 can be made extremely small. Therefore, the far-end crosstalk that occurs between the cables bundled on the master station 1 side can be made extremely small, and the master station 1 can receive signals from slave stations with little interference from far-end crosstalk. can be done. As described above, the data transmission device according to the present invention checks the pulse period of the pulse train transmitted by the slave station at the master station,
This sets the gain of the reception amplifier 27 of the master station, but even if the input level of the equalizer 28 of the master station is small and the equalizer 28 cannot perform a sufficient pull-in operation, the pulse period must be checked. Therefore, gain setting can be performed reliably.

In the above embodiment, the gain is set based on the farthest slave station 2c, but the present invention is not limited to this, and the gain can be set based on any slave station. .

(Effects of the Invention) As explained in detail above, according to the data transmission device of the present invention, the transmission level of the slave station is automatically selected according to the cable length of each dedicated cable. It is possible to reduce the level difference in the reception level on the master station side regardless of the difference in the signal level. Therefore, when the dedicated cables are bundled at the master station side, interference due to far-end crosstalk based on signal level differences can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing a data transmission device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a master station, FIG. 3 is a block diagram showing the configuration of a slave station, and FIG. 4 5 is a waveform diagram showing aspects of various pulse train signals transmitted by a slave station, FIG. 5 is a flowchart showing the procedure for establishing a communication path, and FIG. 6 is a diagram for explaining how far-end crosstalk occurs in a conventional data transmission device. It is an overall configuration diagram. 1... Master station, 2a, 2b, 2e...
Slave station, 3a, 3b, 3c... Dedicated cable, 2
2.42...Communication control section, 27...
Variable gain receiving amplifier, 34... Transmitting amplifier, 47... Receiving amplifier, 50... Variable gain transmitting amplifier. Agent Patent Attorney Yoshihiro Hiroshi Hiroshi 10 Kanazumi 4 and Jinmon Figure 1 Sub-station's JL bottom diagram Figure 3 ＾ Rusu train signal status diagram Figure 4 Figure 5

Claims (1)

[Claims] In a data transmission device comprising a master station and a plurality of slave stations respectively connected to the master station by respective dedicated cables, a communication control unit provided in the master station for each of the slave stations is configured to control communication control to each of the dedicated cables. A transmitting section that transmits data to a slave station so that each transmission level at the transmitting end is the same, a receiving section that receives transmitted data from the slave station, and a predetermined predetermined unit for requesting connection of a communication path to the slave station. a first transmitting means for transmitting a first training signal consisting of a pulse pattern via the transmitting section; and a pulse period of a pulse train signal having a predetermined period received by the receiving section as a response to the first training signal. a second training signal including the determined gain information as a response to the pulse train signal; When the second transmitting means transmits via the transmitting unit and the content of the response transmission received by the receiving unit as a response to the second training signal is a training signal requesting a master station to connect a communication path. , a training end processing means for transmitting a third training signal including training end information for communication channel establishment control via the transmitting section, and for performing training end processing in the master station; The communication control unit included in the slave station includes a reception unit that receives transmission data from the master station, a transmission unit that includes a transmission amplifier whose transmission gain can be changed, and a communication control unit that receives the first training signal received by the reception unit. level detection means for detecting in which of a plurality of preset level ranges the reception level of the amplifier is located; gain setting means for setting the transmission gain of the transmission amplifier according to the detected level range; a first transmitting means for transmitting a pulse train signal with a predetermined pulse period indicating a predetermined gain that is set as a response to the first training signal via the transmitter in which the gain is set; determining means for determining whether the gain value indicated by the gain information included in the training signal No. 2 matches the set gain value; a second transmitting means for transmitting the training signal consisting of a predetermined pulse pattern for requesting connection of a communication channel in the case of a match, as a response to the second training signal via the transmitting section in which the gain is respectively set; and training completion processing means for performing training completion processing in its own station based on training completion information included in the third training signal received by the receiving section.