JP2000115226A - Method for detecting collision in lan, collision detector and its terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect collision of data in a LAN branched in terms of high frequencies. SOLUTION: The LAN that is branched in terms of high frequencies is provided with a collision transmission 10 and terminals 30. Each terminal 30 has a detection signal generation section 35 that generates a collision discrimination AC signal, thereby a collision discrimination AC signal Fs is generated in the case of data transmission. Since the Fs is an AC signal, the signal passes through each branching device 20 and propagates up to the collision detector 10. The collision detector 10 superimposes the signals and discriminates collision of data based on an amplitude of the superimposed signal. Since frequencies of the collision discrimination AC signals Fs sent from the terminals 30 differ slightly from each other, a maximum amplitude is surely obtained. When this amplitude is a prescribed amplitude or over, occurrence of collision is discriminated. Thus, access control of the CSMA/CD system is available by using this collision detection method even in the case of the LAN that is branched in terms of high frequencies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a network system for performing bidirectional data communication between terminal devices, and more particularly, to a high-frequency branched LAN using a coaxial cable.
The present invention relates to a data signal collision detection method, a collision detection device, and a terminal device thereof. INDUSTRIAL APPLICABILITY The present invention is applicable to a LAN constructed using CATV and TV coaxial cables provided from the city to each home or office.

[0002]

2. Description of the Related Art Conventionally, there is a system in which a plurality of terminal devices are connected to a transmission line within a predetermined area to transmit and receive data serially. It is called a local area network (hereinafter, referred to as LAN) and includes a transceiver for monitoring data collision, a hub as a data distributor, and each terminal as a data input / output device. And
The transceivers are connected by a coaxial cable, and the transceiver, hub and each terminal are connected by a twisted pair wire. As a typical example, Ethernet based on IEEE802 is well known.

[0003] The transmission system is a baseband system,
In this method, data of 0 and 1 is converted into a biphase voltage and transmitted to a transmission line. 10BASE5 depending on the transmission medium
It is divided into 10BASE2 and 10BASE-T. Its transmission speed is 10 Mbps. The access control method in this case is CSMA / CD (Carrier Sense M).
This method is similar to the method of “ultiple access with collection detection (carrier detection multiple access / collision detection)”. Before transmitting data, it confirms whether or not the channel on the coaxial cable is occupied, that is, whether or not there is a transmission collision. And sending the data with the address of the sender.

Specifically, there is a network system shown in FIG. A plurality of transceivers 200 and 220 are attached to the coaxial cable 300 which is the main line, and the hub 100 and the hub 120
However, a computer device 101 or the like, which is a terminal device, is further connected thereunder. Transceiver 200,22
0 relays data and monitors data collision on the coaxial cable 300. For example, computer device 1
When there is a request for data transmission from 01 through the hub 100, the transceiver 200 itself sends a DC constant current from the current source 201 to the terminating resistor of the coaxial cable 300. Then, the voltage between the lines is compared with the reference voltage Vref by the comparator 202. For example, when a DC constant current for collision detection flows while another terminal device is already using the network, a DC current twice as large as that in a case where transmission is normally performed flows through the coaxial cable 300. . At this time, the voltage between the lines of the coaxial cable 300 exceeds the reference voltage Vref. As a result, it is detected that transmission collision occurs at the start of transmission. In this case, by not transmitting the data signal, the data signal already transmitted on the coaxial cable 300 is protected.

[0005]

However, the conventional LAN network using a hub and twisted pair wires is a bus type, and is a multi-drop system in which a large number of hubs are connected to a trunk coaxial cable. The access control method is a method in which a constant DC current flows through a terminating resistor, and a collision is determined from the voltage between the lines. Therefore, it has not been possible to extend the LAN by branching and distributing the coaxial cable in an alternating manner. Further, in 10BASE5, which is a communication standard, the trunk line length is at most 500 m, and in some cases, it is not possible to cover all necessary areas. Further, the length of the twisted pair wire connected to the hub is limited to 100 m at most. Furthermore, the number of terminals connected to the hub is limited. Therefore, L having a high degree of freedom over a wide range
An AN was not built.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to solve the problems related to the number of terminals of the conventional system and the degree of freedom in the arrangement thereof in the transmission system using the above twisted pair lines. Focusing on this, instead of using DC current, it is possible to detect transmission collisions using AC signals, so that a coaxial cable that can branch AC is used as a transmission line, and a local To form an area network system. The other purpose is already in the city or each office /
Use CATV and TV coaxial cable lines deployed in each home, apply to LANs that can exchange data between terminals at each office / home while maintaining TV functions, and reduce the usage cost. It is.

[0007]

According to a first aspect of the present invention, there is provided a method for detecting a collision in a LAN, the method comprising: modulating a high-frequency carrier with data of Ethernet specifications to form a data signal; To perform data communication between a plurality of terminal devices by transmitting
In the AN, the coaxial cable is applied to a LAN extended by branching at a high frequency using a branching device or a distributor.
When transmitting a data signal to the network, the plurality of terminal devices transmit a collision determination AC signal for collision determination to the network before the data signal and during a period until the transmission of the data signal is completed. A transmission collision in a network is detected based on a magnitude of a signal amplitude. Here, when a plurality of collision determination AC signals are superimposed, the amplitude varies with time. Therefore, the concept of the magnitude of the above amplitude is the maximum amplitude,
Includes everything proportional to the amplitude, such as average amplitude, instantaneous power, and average power.

This network has been expanded by connecting a branching device or a distributor for branching a high frequency to a coaxial cable. For the branching device or the distributor, a transformer coupling element or the like that transmits a direct current and transmits an alternating current is used. The plurality of terminal devices connected to this network are:
Prior to transmission of the data signal, a collision determination AC signal for detecting a transmission collision is transmitted. The collision determination AC signal passes through the splitter or the distributor without reflection, and is transmitted to the entire coaxial cable. Then, a transmission collision is detected based on the magnitude of the amplitude of the collision determination AC signal. Therefore, transmission collision can be reliably avoided, and reliable data communication can be performed. As a result, data communication in which a high-frequency carrier is modulated with Ethernet-specific data is also possible for a LAN in which a coaxial cable is extended by a branching device or a distributor. That is, packet communication using one channel becomes possible. In particular, the present invention can be applied to a case where a LAN is constructed using a CATV network including the above-described branching device or distributor.

According to the collision detection method for a LAN according to the second aspect, a transmission collision is detected by a collision detection device provided in at least one network. This eliminates the need for each of the plurality of terminal devices to include the collision detection device. Therefore, an efficient and inexpensive collision detection method is provided.

[0010] According to the collision detection method for a LAN according to the third aspect, each terminal device provided in the network transmits a collision determination AC signal having a different frequency. Also, at least one
One collision detection device is provided, and the collision detection device detects whether or not the collision determination AC signals of different frequencies are superimposed. Since the collision determination AC signals transmitted from the plurality of terminal devices have different frequencies, when the signals are superimposed, an amplitude that is the sum of the amplitudes of the plurality of collision determination AC signals is always obtained. The transmission collision can be determined based on the amplitude.

[0011] According to the collision detection method for a LAN according to the fourth aspect, the terminal device transmits a collision determination AC signal that is phase-modulated or frequency-modulated by a random function. As a result, when a collision determination AC signal is transmitted from another terminal device, the phase difference and the frequency difference between the two collision determination AC signals change as a function of time. As a result, a peak value whose amplitude is doubled is detected. As described above, by using the collision determination AC signal that is phase-modulated or frequency-modulated by a random function, it is possible to always detect a peak value having a predetermined amplitude or more, and to reliably determine transmission collision. Can be.

According to a fifth aspect of the present invention, the terminal device changes the phase or the frequency during the initial period of the collision determination AC signal. As a result, if a collision determination AC signal is transmitted from another terminal device in a state where a collision determination AC signal having a constant phase or frequency already exists on the network, two collisions occur in this initial period. The phase difference and the frequency difference of the judgment AC signal change as a function of time.
As a result, a peak value whose amplitude is doubled is detected in the initial period. As described above, by shifting the phase or the frequency in the initial period, it is possible to always detect the peak value having the predetermined amplitude or more, and it is possible to reliably determine the transmission collision.

According to a sixth aspect of the present invention, in the LAN collision detection method, each terminal device receives a collision so that the reception level of each collision determination AC signal output from each terminal device received by the collision detection device becomes constant. The method is such that the transmission level of the determination AC signal is adjusted and transmitted. This allows
For example, the transmission level of the collision determination AC signal can be set in accordance with the length of the transmission path and the attenuation by the branching device, and the collision detection device can always receive the collision determination AC signal having a constant amplitude. The collision detection accuracy is improved.
Therefore, the method for detecting a collision in the LAN is not affected by the conditions of the network system.

According to a seventh aspect of the present invention, there is provided a terminal apparatus for use in a LAN for detecting a collision in the LAN, wherein the terminal apparatus transmits a collision determination AC signal and waits until an initial period elapses before the initial period elapses. When a collision signal is not received, a data signal is transmitted to a network, and when a collision signal is received, transmission of a collision determination AC signal is stopped without transmitting a data signal. The terminal device that has transmitted the collision determination AC signal does not transmit the data signal when receiving the collision signal, and transmits the data signal when not receiving the collision signal. Therefore, the terminal device enables reliable data communication without causing data signal collision. Here, the collision signal may be any signal. For example, a signal of a predetermined frequency may be transmitted when a collision is detected, or a signal of a predetermined frequency is always transmitted when a collision is not detected. The output of the signal may be stopped. Further, the signal may be a signal obtained by modulating data indicating a collision.

According to a collision detection apparatus for a LAN according to the present invention, the collision detection apparatus for use in the above-described collision detection method for a LAN receives an AC signal for judging a collision on a network, and the amplitude of the signal is determined. When the value exceeds a predetermined value, a transmission collision is determined and a collision signal is transmitted to the network. A collision signal is sent to all terminal devices connected below the collision detection device, and those terminal devices are controlled. If it is determined that a transmission collision has occurred, a collision signal is transmitted to all of the plurality of terminal devices, and the transmission of a data signal to terminal devices having a transmission request is prohibited. Conversely, if it is not determined that a transmission collision has occurred, no collision signal is transmitted. As a result, the terminal device that has transmitted the collision determination AC signal and has transmitted the data can transmit the data signal. Therefore, the collision detection device controls a plurality of terminal devices and performs reliable data communication.

According to a ninth aspect of the present invention, the collision detecting device in the LAN is connected to another collision detecting device in a tree structure by a coaxial cable and a branch or a distributor. Each collision detection device controls a plurality of terminal devices connected below the collision detection device. Thus, transmission collision can be detected in the shortest path, that is, in the shortest time. Therefore, the collision detection device detects the transmission collision detection most efficiently. The number of connectable terminal devices can be increased by arbitrarily attaching a distributor or a brancher to the collision detection device as needed. Therefore, the collision detection device realizes a local area network having a high degree of freedom.

According to a tenth aspect of the present invention, there is provided a LAN collision detection apparatus applied to a LAN formed on a CATV network.
The collision determination AC signal is transmitted using an empty channel of CATV. This provides a highly convenient collision detection device that can be applied to a LAN using a CATV network.

The method for detecting a collision in a LAN according to claim 11 is applied to a TV wiring network provided in a predetermined area such as one office or one house, and the collision determination AC signal and the data signal are used when the TV is empty. Sent using the channel. A normal TV wiring network is similar to a CATV network.
The coaxial cable is branched and formed. Therefore, by using the collision detection method, the collision detection device, and the terminal device, in addition to the existing TV reception, a LAN within a predetermined area
Can be formed. Therefore, it is a very convenient collision detection method in a LAN.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following examples. (First Embodiment) FIG. 1 is a schematic configuration diagram of a tree-shaped LAN connected at high frequencies using a coaxial cable and a branching device. The collision detection method of the present invention is applied to this LAN. This LAN is largely composed of a collision detection device 10, a branching device 2,
0, a terminal device 30, and a computer device 40 as an input / output device.
Except for the interval between 0, all are connected by a coaxial cable.
The terminal device 30 and the computer device 40 are connected by a twisted pair wire. The branching unit 20 is a directional coupler coupled with a transformer, and a collision signal transmitted from the collision detection device 10 at the time of a transmission collision is branched or distributed from upstream to downstream and transmitted. Conversely, the collision determination AC signal and data signal from each terminal device 30 are transmitted to the upstream side.

Each terminal device 30 transmits a data signal,
The current transmission path use state is determined based on the presence or absence of another carrier on the transmission path. If another carrier exists, the other terminal device 3
Since 0 is transmitting a data signal, no new data signal is transmitted.

On the other hand, when there is no other carrier, the data signal is transmitted. At this time, there is a possibility that the other terminal devices 30 transmit the data signal almost simultaneously. For this reason, each terminal device 30 has a collision determination AC signal generation unit 35 therein, and prior to transmission of the data signal, each of the collision determination AC signal generation units 35 has a high frequency of slightly different frequency for each terminal device. Collision determination AC signal Fs
Is sent. The frequency of the collision determination AC signal Fs is, for example, 26 MHz and is obtained by a crystal oscillator or the like. The difference frequency of each of them is about every 10 kHz to 100 kHz. The collision determination AC signal Fs may be a carrier wave on which the data signal is carried.

The collision detecting device 10 includes a collision detecting section 15 for detecting the collision determining AC signal Fs, and detects the collision determining AC signal Fs transmitted on the coaxial cable. The detection method is a comparison of the amplitude value of the received collision determination AC signal Fs. For example, a computer device 4
0 alone transmits a data signal to the LAN, a collision determination AC signal Fs of frequency Fs1 is output from the collision determination AC signal generator 35 of the terminal device 30 connected thereto via the coaxial cable. Sent to The collision detection device 10 receives the signal at the collision detection unit 15. The waveform is shown in FIG. And its amplitude V
o is compared with a predetermined value Vth by a comparator or the like. If there is only one collision determination AC signal Fs, the collision detection unit 1
5, the amplitude of the signal received is equal to or smaller than the predetermined value Vth, and it is not determined that a transmission collision has occurred. Therefore, the collision signal Fc is not transmitted from the collision detection device 10, and the collision determination AC signal Fs
Transmits the collision determination AC signal Fs and transmits a data signal after a predetermined initial period has elapsed.

On the other hand, if there is a data signal transmission request from the other computer device 40 within the LAN with a slight delay, the terminal device 30 connected thereto also transmits the collision determination AC signal Fs of frequency Fs2 to the collision detection device. It is sent to 10. There is a branching device 20 on the way, but since the branching device 20 is connected at a high frequency, its signal is transmitted to the collision detection device 10. In this state, two collision determination AC signals are superimposed on the coaxial cable. The collision detection device 10 includes a frequency Fs1 and a frequency Fs2.
Of the two collision determination AC signals Fs. The amplitude is doubled when the phases match (FIG. 2B). Conversely, when the phase is shifted by 180 degrees, it becomes almost zero. Collision determination signal F sent from terminal device 30
Since the phase or frequency of s is slightly different, the phase may surely match, and the maximum amplitude at that time exceeds the predetermined value Vth. Therefore, in this case, a transmission collision is determined.

When a collision is determined, a collision signal Fc of, for example, about 30 MHz is transmitted to all the terminal devices 30 in the LAN as shown in FIG. Then, the terminal device 30 that is about to start transmission, that is, the terminal device 30 that has newly output the collision determination AC signal Fs, receives the collision signal Fc.
, The output of the collision determination AC signal Fs is immediately stopped, and no data signal is transmitted. Thus, even if the data transmission request, that is, the collision determination AC signal Fs is transmitted with a slight delay, the presence or absence of a collision is reliably determined, and the transmission of the current data signal is protected.

As described above, when transmitting a data signal, a transmission collision is detected by two-stage detection of detection of another carrier and detection by the collision determination AC signal Fs. Therefore, it can be detected reliably. Also, when transmitting a data signal, it detects whether there is another carrier or data in the transmission path, and outputs the above-mentioned collision determination AC signal and performs collision determination when there is no other carrier or data. However, without detecting the presence of other carriers or data, it is also possible to determine whether the transmission path is idle or in use by merely outputting the collision determination AC signal and determining the collision of the signal.
That is, the collision determination AC signal is output even while the data is being transmitted. Therefore, since the collision determination described above can be performed while data is being transmitted, when a terminal device that is going to transmit data receives a collision detection signal, the transmission path is determined to be in use and the data is determined to be in use. Is stopped, and the terminal device that has already transmitted data continues to transmit data. Even in this case, a reliable collision determination can be made. It should be noted that the data signal output from the terminal device 30 is converted into a predetermined downlink channel frequency in the collision detection device 10 and is returned to the coaxial cable. Thereby, data communication between the terminal devices 30 becomes possible.

The splitter 20 can be bidirectional. Further, a bidirectional distributor (not shown) can be used instead of the branching device 20. In this case, the collision detection device 10 does not return the uplink data signal. That is, the data signal output from the terminal device 30 is
To be transmitted to the downstream side by these branching devices 20 and bidirectional distributors, the terminal device 3 uses the same carrier frequency.
Packet communication between 0 is possible.

Also, the frequencies Fs1 and Fs2 of the collision determination AC signal transmitted from the terminal device 30 are greatly different from each other,
As shown in FIG. 2C, the collision detection device 10
It may be detected by multiplying and demodulating. When two different collision determination signals Fs are square-demodulated, | Fs1−Fs2 |
The reverberation line of the difference frequency appears. If the maximum amplitude of the choke line exceeds a predetermined value Vth, it may be determined that a transmission collision has occurred.

In order to more reliably detect a collision,
A voltage-controlled crystal oscillator V
It is desirable to use CO and input a random function to it. When a voltage waveform based on a random function is input, a collision determination AC signal Fs that is randomly phase-modulated or randomly frequency-modulated is obtained. FIG. 2D shows the collision determination AC signal Fs which is randomly frequency-modulated and the signal waveform which is superimposed. Since it is random, the superimposed signal has a portion that definitely exceeds the predetermined value vth.
As a result, transmission collision can be detected more reliably, and detection accuracy can be increased. Alternatively, the frequency or the phase may be shifted only for a predetermined initial period of the collision determination AC signal, and the frequency may be set to be constant after the initial period has elapsed. If there is a collision determination AC signal whose frequency or phase is already constant in the transmission path, the relative phase relationship between the two collision determination AC signals fluctuates with time in the initial period. Are always present, and there are always times when a double amplitude is obtained.

(Second Embodiment) FIG. 3 shows a terminal device 3 of the present invention.
FIG. This terminal device 30 is applied to the collision detection method in the LAN of the first embodiment. FIG.
FIG. 1 shows a configuration diagram of a collision detection device 10 which is also used for a collision detection method in a LAN. Terminal device 30 of the present invention
The Ethernet interface 31, a modulator 32 for modulating a carrier with Ethernet-specific data, a demodulator 33 for extracting data from the modulated signal, a collision signal detector 34 for detecting a collision signal from the collision detector 10, A collision determination AC signal generator 35 for transmitting a high-frequency signal for detection, a pilot signal BPF (band-pass filter) 38 for extracting a pilot signal transmitted from the collision detection device 10, and a comparison between the pilot signal amplitude and the reference signal amplitude. And a differential amplifier 37 for controlling the voltage-controlled attenuator 36 for correcting the attenuation of the transmission line. The modulation includes amplitude modulation, frequency modulation, and phase modulation. In this embodiment, amplitude modulation is used. The transmission system is a broadband system in which frequencies are multiplexed.
M to 112 MHz band, but 150 MHz to
A 450 MHz band is allocated, and bidirectional communication is performed. Also, 30 MHz is selected as the collision signal Fc.

The data signal input from the computer device 40 is transmitted to a twisted pair line in a predetermined communication format (10BASE-T). The data signal transmitted to the twisted pair line is transmitted via the Ethernet interface 31.
The signal is transmitted to the modulation unit 32. In the modulator 32, for example, the upstream carrier Fu (60 MHz) is amplitude-modulated based on the data signal, and is transmitted to a network formed by a coaxial cable via a voltage-controlled attenuator 36. In order to avoid data signal transmission collision, first, the demodulator 33 checks the current use status of the transmission path. For example, the determination is made based on the presence or absence of another carrier or the presence or absence of data. If another carrier is detected, data transmission is not performed.

If no other carrier is detected, the transmission of the data signal is further notified to the collision detection device 10 on the network to avoid simultaneous transmission collision. This is performed by transmitting a collision determination AC signal Fs of a predetermined frequency from the collision determination AC signal generation unit 35.

The collision detection device 10 detects the presence or absence of a transmission collision from the amplitude value of the collision determination AC signal Fs transmitted from each terminal device 30. Therefore, the amplitude of each collision determination AC signal Fs of each terminal device 30 input to the collision detection device 10 before detection needs to be set to be constant. In general, the transmission path from the collision detection device 10 to each terminal device 30 is different, so that the attenuation is also different.
A voltage-controlled attenuator 36 is provided to adjust the amount of attenuation to a constant value.

A method of adjusting the voltage control type attenuator 36 will be described. Now, the collision determination AC signal Fs output from the crystal oscillator 35a inside the collision determination AC signal generation unit 35
Is Vs, the attenuation rate by the attenuator 35b is A, the reference voltage level Vr is A × Vs, and the pilot signal B is
The reception voltage level of pilot signal Fp output from PF 38 is set to Vp.

As shown in FIG. 3, the reference voltage level Vr is input to the inverting input terminal of the differential amplifier 37, and the received voltage level Vp output from the pilot signal BPF38 is input to the non-inverting input terminal of the differential amplifier 37. ing. The output controls the voltage-controlled attenuator 36 in proportion to Vp-Vr, and the amount of attenuation is determined. That is, the feedback amount is applied to the attenuation amount of the voltage-controlled attenuator 36 so that the reception voltage level Vp of the pilot signal Fp at the terminal a of the voltage-controlled attenuator 36 becomes equal to the predetermined reference voltage level Vr.

For example, if the voltage level of the pilot signal Fp at the output terminal of the collision detection device 10 is Ve, Ve
-Vp = Ve-Vr = (transmission path loss) + (loss due to the voltage-controlled attenuator 36) holds. Since the voltage levels Ve and Vr are constant, the amount of attenuation between the output terminal of the collision detection device 10 and the terminal a of the voltage-controlled attenuator 36 of each terminal device 30 can be made equal. That is, when the transmission path loss is large, the loss due to the voltage-controlled attenuator 36 is suppressed, and when the transmission path loss is small, the attenuation is applied by the voltage-controlled attenuator 36, and the total loss is always a constant value. (Ve−Vr).

Therefore, if the voltage level Vs of the collision determination AC signal Fs input from the terminal a of the voltage-controlled attenuator 36 of each terminal device 30 is the same in all terminal devices 30, the total loss as described above is obtained. Is constant, the voltage level of the collision determination AC signal Fs received by the collision detection device 10 is the same. Thus, the voltage-controlled attenuator 36 is adjusted. Note that the collision determination AC signal generating unit 3
Reference numeral 5 denotes a crystal oscillator 35a set to a predetermined frequency, an attenuator 35b, and a switch 35c. When data is transmitted, the switch 35c is turned on, and the collision determination AC signal Fs is transmitted from the crystal oscillator 35a. I do. When adjusting the voltage-controlled attenuator 36, the switch unit 3
5c is turned off and used.

As described above, since the collision determination AC signal Fs is controlled with high accuracy, the collision detection device 10 uses the collision detection AC signal Fs at a reception voltage level equal to or higher than the reception voltage level, for example, 1.5
If a peak voltage level twice or more is detected, it is determined that two or more collision determination AC signals Fs are superimposed on the transmission path, and it is determined that a transmission collision has occurred. In this case, the collision detection device 10 sends out a collision signal Fc on the network. The collision signal detection unit 34 of each terminal device 30
This collision signal Fc is received. When this signal is detected, each terminal device 30 immediately stops transmitting the collision determination AC signal Fs and does not transmit the data signal. Therefore, even if transmission requests are issued almost at the same time, transmission collision of data signals is avoided. Further, even if a predetermined initial time required for collision determination by the collision detection device 10 has elapsed, the collision signal Fc
Is not received, the terminal device that has transmitted the collision determination AC signal Fs continuously transmits the collision determination AC signal Fs, and transmits the data signal after the elapse of the initial time. In this way, collisions in data transmission are avoided and data communication is performed.

Next, the collision detecting device 10 will be described. As shown in FIG. 4, the collision detection device 10 includes an Ethernet interface 11, a modulation unit 12 that modulates the downlink carrier Fd according to the Ethernet specification, a demodulation unit 13 that extracts data from an uplink modulation wave signal (data signal), and each terminal device 30. Determination AC signal Fs issued for collision detection from
, The extracted collision determination AC signal F
s, a collision detection unit 15 that detects a collision, and a collision signal generation unit 1 that generates a predetermined collision signal Fc to notify the collision.
6. A pilot signal generator 15a for adjusting the attenuator 36 of the terminal device 30, a distributor 17 for distributing input / output of high-frequency signals, and a digital signal distributor for directly connecting a plurality of computer devices 40 And a hub 18.

The distributor 17 receives the collision determination AC signal Fs from each terminal device 30 prior to the data signal.
The frequency of the collision determination AC signal Fs is about 26 MHz.
It differs every H to 100 KHz. The input collision determination AC signal Fs is extracted by the BPF 14 and sent to the collision detection unit 15. The collision detector 15 receives the single or superimposed collision determination AC signal Fs, and determines whether or not a collision has occurred based on the amplitude of the received signal. If it is single, its amplitude is a predetermined value, and if it collides, its amplitude is about twice that of the single case.

FIG. 5 shows the details of the collision detection unit 15. The collision detection unit 15 includes an attenuator 15b, a switching device 15
c, 15f, an amplifier 15d, a differential amplifier 15g, and a detector 15e. This is because, when there are a plurality of collision determination AC signals Fs on which the output signal of the BPF 14 is superimposed, a collision detection signal is output from the final OR unit 15j,
In the case of a single collision determination AC signal Fs, no collision detection signal is output.

Therefore, first, a single collision determination AC signal Fs
Needs to be stored at a high frequency. Since the signal strength of the single collision determination AC signal Fs is set at, for example, the point A to about 70 db by the voltage-controlled attenuator 36 described above, the memory is stored by the pilot signal generator 19 and the attenuator 15b. It is obtained by setting point B to 70 db. Further, the collision determination AC signal Fs that has passed through the BPF 14 needs to be detected without an error due to a circuit element. Therefore, the two switching devices 15c and 15f
And an amplifier 15d and a detector 15e.
The output is compared and detected by a single differential amplifier 15g. By using the same element by switching, an error due to a circuit element can be avoided.

For example, when a plurality of collision determination AC signals Fs having different frequencies pass through the BPF 14, the amplitude is 2
In some cases, the signal amplitude at point A is 73 db. On the other hand, point B stores a single-frequency high-frequency signal of 70 db. These high-frequency signals are amplified by the amplifier 15d and rectified by the rectifier 15e, and the rectified signal is input to the differential amplifier 15g.
Therefore, the difference 3db is amplified and, for example, 'H' is output from the OR unit 15j via the output terminal 15h of the differential amplifier 15g. On the other hand, the single collision determination AC signal Fs
After passing through F14, a signal intensity of 70 db is measured at both points A and B, so that there is no difference in intensity. Therefore, the output of the output terminal 15h of the differential amplifier 15g also becomes 0, and the OR
No collision detection signal is output from j.

When a collision is determined, the collision detector 15 triggers the collision signal generator 16 to generate a collision signal Fc of, for example, 30 MHz, as shown in FIG. This collision is sent to all the terminal devices 30 via the distributor 17 and the Ethernet interface 11, and notifies all the other terminal devices 30 of the transmission collision. Thereby, transmission collision is avoided.

Also, as shown in FIG.
In some cases, data is directly input from the hub 18 connected to the device via a twisted pair line and transmitted. At this time, the RS terminal of the Ethernet interface 11 becomes active. The transmission collision between the direct data transmission from the collision detection device 10 and the data transmission from each terminal device is determined by using this active signal.

For example, when the collision determination signal FS is input from any of the terminal devices 30, the differential amplifier 1 shown in FIG.
Input terminal 15 to which 5 g of collision determination AC signal Fs is input
potential of g ₁ is increased, one input terminal of the AND circuit 15i becomes active. Therefore, the active signal of the RS terminal is input to the other input terminal of the AND unit 15i,
By taking the logical product, a transmission collision between the two is determined. This determination signal is ORed with a collision detection signal between the terminal devices by the OR unit 15j, and is output as a comprehensive collision detection signal. This collision detection signal triggers the collision signal generator 16 to stop data transmission from all the terminal devices 30 as described above. As a result, even when data is directly input to the collision detection device 10, collision determination is performed and transmission collision is avoided.

As described above, even in a tree-like LAN system branched in high frequency using a coaxial cable,
If the terminal device 30 and the collision detection device 10 as described above are used, the collision of the data signal is reliably detected and the transmission data does not collide. Accordingly, an excellent LAN collision detection device and terminal device capable of performing reliable data communication over an extremely wide range compared to the related art are provided. In this system, the distributor 17 may be bidirectional. In this case, the collision detection device 10 does not return the uplink data signal. That is, the data signal output from the terminal device 30 is also transmitted downstream by these distributors 17, so that packet communication between the terminal devices 30 can be performed using the same carrier frequency.

(Third Embodiment) FIG. 6 shows a configuration diagram of a tree-shaped LAN using a plurality of collision detection devices of the present invention. In the present embodiment, a new collision detection device 50 is sequentially added below the collision detection device 50. Thereby, the computer device 40 can be further added. This corresponds to a so-called hub that extends the network with twisted pair wires. In other words, it becomes a hub that can further expand a high-quality network with a coaxial cable. The devices having the same functions as those of the first embodiment are denoted by the same reference numerals.

FIG. 7 shows a configuration diagram of the collision detection device 50.
The collision detection device 50 is formed using the collision detection device 10 of the second embodiment. The collision detection device 50 is characterized by inputting and outputting a data signal, which is a modulation signal, on the upstream side. This is achieved by adding an A1 block circuit 51 to the hub 18 of the collision detection device 10. The A1 block circuit 51 is equivalent to the A1 block circuit 39 (FIG. 3) for converting the baseband signal used in the second embodiment into a modulation signal of Ethernet specifications. This forms a hub applied to a network using a coaxial cable.

That is, the upstream input / output buffer device 56
The data signal (modulation signal) input from the A1 block 51 is once converted into a 10BASE-T format signal by the A1 block 51, and then the hub 18, the Ethernet interface 11,
After passing through the modulating unit 12, the plurality of distributors 17 are again modulated as modulated signals.
Is output downstream. At this time, the carrier frequency is Fd
It is. Conversely, the data signal of the carrier frequency Fu input from any of the distributors 17 on the downstream side is transmitted from the input / output buffer device 56 on the upstream side via the reverse path.
That is, the hub uses a coaxial cable.

The terminal devices 50 formed in this way are connected in a tree shape, and a plurality of terminal devices 3
0 and the computer device 40 are connected. Since each of the collision detection devices 50 detects a collision between the directly connected terminal devices 30 in the same manner as in the second embodiment, it controls the collision in the shortest time. Accordingly, the collision detection system detects the collision most efficiently. Further, each collision detection device 50 can include a plurality of terminal devices 30 and a computer device. Therefore, the collision detection device can increase the number of connections of the computer device 40 as needed. In addition, since a coaxial cable is used, it is less susceptible to disturbances such as electromagnetic wave noise. Further, the number of connected computer devices 40 can be adjusted optimally by the branching device 20 that branches at a high frequency. Therefore, the collision detection apparatus has a high access control efficiency and a high-quality LAN with a high degree of design freedom.

(Fourth Embodiment) FIG. 8 shows a LAN using a CATV network. This embodiment is applied to this LAN. This CATV network is an existing CATV network deployed in each home or office using a coaxial cable.
The frequency used for CATV transmission is separated into two bands. One is an upstream band of 10 to 55 MHz in the station direction, and the other is a downstream band of 70 to 770 MHz to the terminal device side. The upstream band is mainly used for data information communication, and the downstream band is used for television signals such as video signals (hereinafter, referred to as TV signals). Note that 55 MHz to 70 MHz is a guard band for separating the upstream band and the downstream band. The collision detection device of this embodiment detects a collision of data signals using these frequency bands and forms a LAN. This LAN is connected from the CATV coaxial cable 60 to the TV.
Collision detection device 70 for capturing signals, TV signal and LA
It comprises a splitter 20 for splitting a high frequency signal used for N, a terminal device 30, a computer device 40, and a TV device 80. By providing a collision detection device having the same function as the collision detection device 70 at the downstream end of the optical / electrical conversion device 61,
It is also possible to determine a collision in the communication between the LAN of this system and the LAN of another system connected to the CATV coaxial cable 60.

FIG. 9 shows a schematic configuration diagram of the collision detection device 70. The collision detection device 70, in order to relay the TV signal,
The third embodiment is characterized in that an amplifier for amplifying a TV signal and sending it to a lower terminal is added to the collision detection device 50 of the third embodiment. The data signal transmission / reception method and the collision detection method are the same as those of the collision detection device 50. The collision detection device 70 is a TV
An input / output buffer device 71 for inputting / outputting a signal, a data signal / collision signal, a distributor 74, a BPF 72 for extracting a TV signal from a multiplexed high-frequency signal, an amplifier 73 for amplifying a TV signal, used in the second embodiment. 10BASE-
An A1 block circuit 75 for modulating a T-system data signal to a predetermined Ethernet specification and sending it out over a coaxial cable, a B1 block circuit 76 having a function of detecting a data signal collision, and a 10BASE-T system distributor And a hub 77. The A1 block circuit 75 and the A1 block circuit 39 (FIG. 3) of the first embodiment, and the B1 block circuit 76 and the B1 block circuit 19 (FIG. 4) of the second embodiment are equivalent circuits.
Alternatively, the optical / electrical conversion device 61 may have the function of the collision detection device 50 as described in the third embodiment.

The TV signal transmitted from the CATV station is transmitted to the photoelectric converter 61 by an optical fiber, and thereafter, is distributed by a CATV coaxial cable. Collision detection device 7
Numeral 0 is connected to this CATV coaxial cable by an input / output buffer device 71. From the TV signal input to the input / output buffer device 71, only the TV signal is taken out by the BPF 72, and is passed through an amplifier 73 and a distributor 74 to each TV device 80.
Sent to. As a result, CA in ordinary small areas
A TV network is formed.

On the other hand, the data signal input from the distributor 74 is sent to the higher order via the B1 block circuit 76, the hub 77, the A1 block circuit 75 and the input / output buffer 71. The data signal input from the input / output buffer 71 follows the reverse route and is sent to each terminal device via the distributor 74. The detection signal Fs for collision detection is collected by the distributor 74 from each terminal device 30 and processed by the B1 block circuit 76. If there is a collision, a collision signal Fc is transmitted to each terminal device through the reverse route.

The frequency band used at this time is, for example, any one of the frequency bands of 10 to 55 MHz for the carrier wave of the upstream data and the frequency band of 770 MHz or more for the carrier wave of the downstream signal. Any frequency band of the guard band is used for Fs. Therefore, if the collision detection device 70 is connected to a CATV network, an independent small-scale LAN can be used without affecting the CATV system.
Is formed. Since these LANs use the existing CATV network, there is no need to newly provide a LAN cable. Therefore, if this collision detection device 70 is applied, an inexpensive and highly convenient small-scale LAN can be realized.

(Modifications) The embodiment of the present invention has been described above, but various other modifications are conceivable. Second
Also in the fourth to fourth embodiments, as described in the first embodiment, the collision determination AC signal may be a signal having a slightly different frequency for each terminal device. A control-type crystal oscillator VCO may be used, and a voltage waveform based on a random function may be given to the control-type crystal oscillator VCO to obtain a collision-determining AC signal Fs that is randomly modulated. Not limited to a random function, a triangular wave having a different frequency may be used. In addition, any type of voltage waveform can be used as long as the voltage waveform can reliably extract the maximum amplitude by sweeping the phase. Further, the phase or frequency may be changed during the initial period for transmitting the collision determination AC signal, and thereafter, may be made constant. Since the VCO can arbitrarily set the oscillation frequency by the voltage, the VCO can provide a frequency corresponding to the frequency response of the collision detection unit 15. Therefore, collision detection can be performed in the shortest time.

Further, in the fourth embodiment, the unused band of CATV is used for the collision determination AC signal Fs for collision detection, but an arbitrary frequency band may be used as long as the band does not hinder the CATV system. Can also. For example, a vacant channel of a TV signal can be used. Further, in the fourth embodiment, the collision detection method and the collision detection device in the LAN according to the present invention and the terminal device thereof are applied to the existing CATV network.
Office Home Office) or a TV network deployed in a small area such as an apartment. Also in this case, a small-scale LAN can be formed in addition to normal TV reception.

In the first to fourth embodiments, the collision detection devices 10, 50, and 70 output a collision signal when a transmission collision is detected, and output a collision signal when no transmission collision is detected. Although it does not output the collision signal,
A signal indicating that transmission collision has not been detected may be transmitted. Further, when a transmission collision is not detected, a pilot signal of a predetermined frequency is output, and when a transmission collision is detected, the output of the pilot signal may be stopped.

In all of the above embodiments, the carrier Fd of the downstream data signal output from the collision detection device and the carrier Fu of the upstream data signal input to the collision detection device have different frequencies. May be used. That is, the frequency band may not be divided between the uplink and the downlink for the data signal.

Although various other modifications are conceivable, the coaxial cable is branched at a high frequency, and the terminal device has a tree shape.
In a network constructed in a star shape, any type of collision detection method, collision detection device, and terminal device may be used as long as a collision between data signals is detected using a collision determination AC signal.

[Brief description of the drawings]

FIG. 1 is an LA to which a collision detection method according to a first embodiment is applied;
FIG.

FIG. 2 is a change diagram of a collision determination AC signal due to a collision.

FIG. 3 is a block circuit diagram of a terminal device according to a second embodiment.

FIG. 4 is a block circuit diagram of a collision detection device according to a second embodiment.

FIG. 5 is a circuit diagram for detecting a collision according to a second embodiment of the present invention.

FIG. 6 illustrates an LA using the collision detection device according to the third embodiment.
FIG.

FIG. 7 is a configuration diagram of a collision detection device according to a third embodiment of the present invention.

FIG. 8 shows a LAN using the collision detection device according to the fourth embodiment.
FIG.

FIG. 9 is a configuration diagram of a collision detection device according to a fourth embodiment.

FIG. 10 is an explanatory diagram of a conventional collision detection method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Collision detection apparatus 11 Ethernet interface 12 Modulation part 13 Demodulation part 14, 72 Band pass filter 15 Collision detection part 16 Collision signal generation part 17, 74 Divider 18, 77 Hub 19 Pilot signal generator 20 Branch device 30 Terminal device 35 Collision determination AC signal generator 36 Voltage-controlled attenuator 37 Differential amplifier 40 Computer device 50, 70 Collision detector 56, 71 Input / output buffer device 60 CATV coaxial cable 61 Photoelectric converter 73 Amplifier

Claims (11)

[Claims] 1. A LAN for performing data communication between a plurality of terminal devices by modulating a high-frequency carrier wave with data of Ethernet specifications and transmitting the data signal to a network, using a branching device or a distributor. The plurality of terminal devices transmit the data signal to the network by preceding the data signal when the terminal device transmits the data signal to the network.
Sending a collision determination AC signal for collision determination to a network during a period until the transmission of the data signal ends, and detecting a transmission collision in the network based on the magnitude of the amplitude of the collision determination AC signal on the network. A collision detection method in a LAN, characterized in that: 2. The LAN collision detection method according to claim 1, wherein the transmission collision is detected by at least one collision detection device provided in the network. 3. The method for detecting a collision in a LAN according to claim 2, wherein said terminal device transmits a collision determination AC signal having a different frequency for each terminal device. 4. The method for detecting a collision in a LAN according to claim 1, wherein said terminal device transmits said collision determination AC signal which is phase-modulated or frequency-modulated by a random function. 5. The method according to claim 1, wherein the terminal device changes a phase or a frequency in an initial period of the collision determination AC signal. 6. Each terminal device adjusts the transmission level of the collision determination AC signal so that the reception level of each collision determination AC signal output from each terminal device received by the collision detection device becomes constant. 6. The method for detecting a collision in a LAN according to any one of claims 1 to 5, wherein the transmission is performed after transmission. 7. A terminal device used in the collision detection method in a LAN according to claim 1, wherein the terminal device transmits the collision determination AC signal until an initial period elapses. When the collision signal is not received from the collision detection device, the data signal is transmitted to the network, and when the collision signal is received, without transmitting the data signal, the collision determination AC signal is transmitted. A LAN terminal device for stopping transmission. 8. A collision detection apparatus used in the collision detection method in a LAN according to claim 1, wherein the collision detection AC signal is received on the network, and the collision detection AC signal is received. A collision detection device for a LAN, which determines a transmission collision when the amplitude exceeds a predetermined value and sends a collision signal to the network. 9. The collision detection apparatus according to claim 8, wherein the collision detection apparatus is connected to another collision detection apparatus in a tree structure by the coaxial cable and the splitter or the distributor. . 10. The collision detection device is applied to a LAN formed on a CATV network, and the collision determination AC signal is a CA signal.
10. The collision detection apparatus in a LAN according to claim 8, wherein the transmission is performed using an empty channel of the TV. 11. The method according to claim 1, wherein the method for detecting a collision in a LAN is applied to a TV wiring network provided in a predetermined area, and a LAN is formed by using a TV free channel. The LA according to any one of the above,
N, the collision detection method.