JP2691005B2 - Communication method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a communication system using a tree-type coaxial transmission line such as a bidirectional CATV transmission line.

[Prior Art] Conventionally, in a communication method using a tree-type coaxial transmission line such as a bidirectional CATV transmission line, when an alarm signal or a terminal state is transmitted from a device on the terminal side to a CPU on the center side, It looked like this: That is, the CP on the center side
U sends a polling signal to each terminal device in the order of its address. The terminal device responded to this polling signal, and it was designed to deliver the alarm signal and the upstream data such as the state of the terminal to the CPU on the center side.

In such a communication method, it takes time to poll all terminals when the number of terminals is large, so the terminals are divided into several groups, and a repeater called a hub is provided in the middle of the transmission path for each group. By the CP of the center
A double polling method is implemented in which polling is performed separately between U and the hub and between the hub and the terminal.

However, this double polling system has a problem in that the system cost becomes high because a hub is provided in the middle of the transmission path, and the maintainability and installation restrictions are limited.

Therefore, in recent years, while each terminal device waits for uplink data, it transmits at an arbitrary time, and in case of collision, it retransmits with a random time delay different for each terminal and CSMA / CD (carrier sense).・ Multi-access / collision direction) I such as Ethernet LAN
It has come to be used in conformity with the EEE802.3 standard.

[Problems to be Solved by the Invention] However, these contention methods and CSMA / C
The D method has a drawback in that when the number of terminals increases, the frequency of collisions increases and the communication efficiency decreases significantly.

The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a communication method capable of transmitting information from a large number of terminals to the center side in a short time.

[Means and Actions for Solving the Problem] According to the present invention, when a terminal device responds to inquiry data from a center CPU, a terminal desiring to transmit has a response window time corresponding to bits in which its own address is determined. When a collision occurs with another station, the transmission right is obtained by responding to the re-inquiry from the center CPU with the response window time corresponding to the address of the next bit defined by the own station. By sending the upstream data to the central CPU only by the terminal, it becomes possible to transmit the data to the central CPU in a short time even when there are many terminals.

[Embodiment] An embodiment in which the present invention is applied to a bidirectional CATV transmission line will be described below with reference to the drawings.

Fig. 1 shows the circuit configuration. 11 is a transmission line by a coaxial cable for transmitting TV signals such as TV broadcast wave radio waves and independent broadcast wave signals from VTR to the terminal side, 12 is a transmission line 11
A frequency converter for frequency conversion of the upstream signal from the terminal side via the ED, and sending it to each terminal as a downstream signal, 13 is a transmission line
A distributor / combiner that connects 11 and the frequency converter 12 to separate and combine a TV signal and a data signal, 14 is a central CPU, 15 is a display device connected to the central CPU 14, and 16 is an RF that performs modulation / demodulation at high frequencies. A modem, 17 is a branching device that connects the transmission line 11 and the RF modem 16, and 18 is a bidirectional amplifier. Also, 19
Is a branching device, 21 is a distributor / combiner, 22 is an RF modem, and 23 is a terminal device.

The center CPU 14 inquires whether or not there is upstream data of each terminal at regular time intervals. The data frame structure of the data sent to the terminal side in this case is shown in FIG. That is, the data frame is composed of each frame of preamble, start delimiter, control, partner address, own station address, data, error check and stop delimiter. The preamble frame is a pattern for pulling in the bit synchronization frame synchronization of the communication partner, here each terminal device, and is usually composed of a simple repeating pattern such as "1010 ...". The start delimiter frame and the end delimiter frame are frames to which special patterns indicating the start and end of data are assigned. The control frame is a frame for controlling the signal processing of the receiving station by inquiring, re-inquiring, responding, confirming, and distinguishing the data contents of data. In addition, the partner address frame and the own station address frame are addresses indicating the communication partner and the own station.
When communicating with 4, the center CPU14 on the terminal side
It is also possible to simplify the address of and to send. The data frame is a frame indicating alarm information collection of the terminal, status information from the terminal, and the like, and the error check frame is a frame in which an error status of the transmission data is calculated by a generator polynomial or the like and notified.

Next, the operation of the above embodiment will be described with reference to FIGS. 3 and 4.

FIG. 3 shows an outline when three terminal devices 33 to 33 are connected to the bidirectional CATV line. Here, the address of the terminal device 31 is “39 _H (00111001)” and the address of the terminal device 32 is "46 _H (01000110)", set the address of the terminal device 33 to "4
9 _H (01001001) ”, and its operation algorithm is shown in FIG. 4 below.

The inquiry data “S” is sent from the center CPU 14 to each of the terminal devices 31 to 33. Terminals 31-33 are the centers
When there is a request to send data to the CPU 14, the response data "R" is sent in response to the inquiry data "S". The terminal devices 31 to 33 simultaneously respond to the response data “R”.
Are transmitted, they collide on the transmission line 11 and are destroyed. The center CPU 14 sends re-inquiry data “W” in response to this. After the terminal apparatus 31 to 33 which has received the re-query data "W", viewed upper two bits of the address of the own station, in response window time RA ₁ time determined, corresponding to the 2 bit 1 / The response data “R” is transmitted again at the designated time of 4. In this case, the terminal devices 32 and 33 recognize the upper 2 bits "01" of their own addresses, and simultaneously transmit the response data "R" again at the timing "01" of the response window time RA ₁ . However, again, the response data "R" collides on the transmission line 11 and is destroyed. This collision was confirmed at the terminal device 31,
The terminal device 31 refrains from transmitting the response data “R” at the next “00” timing within the response window time RA ₁ until the next inquiry data “S” is transmitted. Also center CP
U14 detects this re-collision and transmits re-inquiry data "W" again.

After receiving the re-inquiry data “W”, the terminal devices 32 and 33 recognize the third and fourth bits “00” of their own address, and respond again at the timing “00” within the response window time RA ₂ . Data "R" is transmitted at the same time. Here again, the response data “R” collides on the transmission line 11 and is destroyed. The center CPU 14 detects this collision and again sends the re-inquiry data “W”.

After receiving the re-inquiry data “W”, the terminal device 33
It recognizes the fifth and sixth bits "10" in the local address, and transmits the "R" again the response data at the timing of "10" in the response window time RA _3. Here, the response data “R” is finally delivered to the center CPU 14 via the transmission line 11. The center CPU 14 recognizes this and transmits the confirmation data “A”. On the other hand, the terminal device 32 "1 in the response window time RA ₃
The transmission of the response data “R” from the terminal device 33 at the timing of “0” is recognized, and the transmission of the response data “R” at the timing of “01” within the response window time RA ₃ is next transmitted from the center CPU 14. Please refrain from sending "S".

After receiving the confirmation data “A” from the center CPU 14, the terminal device 33 transmits the data “D” including alarm information and the like to the center CPU 14 via the transmission path 11.
After receiving the data “D” from the terminal device 33, the center CPU 14 executes processing such as displaying alarm information according to the content of the data. And after that processing, the central CPU14
Sends inquiry data “S” to the terminal devices 31 and 32, sequentially absorbs upstream data in the same procedure as above, and executes the processing.

In the above embodiment, the addresses of the terminal devices 31 to 33 are set to 8
Although the example of the case of the bit configuration has been described, the present invention is not limited to this, and it is also possible to realize with a bit number larger, in which case the number of re-inquiries increases.

Further, in FIG. 1 described above, since the frequency converter 12 is provided on the center side, the RF modems 16 and 22 can transmit at the same upstream signal frequency. Therefore, the center CPU 14 can be relocated not only to the center side but also to the terminal side.

[Effects of the Invention] As described in detail above, according to the present invention, when the terminal device responds to the inquiry data from the center CPU, the terminal desiring the transmission responds to the response window corresponding to the bits for which its own address is determined. In response to the time, if there is a collision with another station, in response to a re-inquiry from the center CPU, the transmission right is granted by responding with the response window time corresponding to the address of the next bit specified by the own station. Since only the obtained terminal sends the upstream data to the center CPU, it is possible to provide a communication method that enables the data to be transmitted to the center CPU in a short time even when there are many terminals.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is a block diagram showing a circuit configuration on a center side and a terminal side, FIG. 2 is a diagram showing a data frame configuration, and FIG. 3 is a specific connection. FIG. 4 is a diagram illustrating the configuration, and FIG. 4 is a diagram showing the content and timing of the data transmitted and received in FIG. 11 …… Transmission line, 12 …… Frequency converter, 13,21 …… Distribution combiner, 14 …… Center CPU, 15 …… Display unit, 16,22 ……
RF modem, 17, 19 …… Brancher, 18 …… Bidirectional amplifier, 23,
31-33 …… Terminal device.

Claims (1)

(57) [Claims] 1. A center CPU for controlling communication operation on a tree-shaped coaxial transmission line, and terminal devices of a plurality of stations connected to the coaxial transmission line, wherein the terminal device is used for inquiry data from the center CPU. Is a response method, and if there is reply data, it is a communication method that sends the send data to the center CPU, and the time when the center CPU sends the inquiry data composed at regular time intervals and multiple terminals. In response to the response window time provided with a plurality of response times to the device, the terminal device desiring to transmit responds to the response window time corresponding to the designated address bits from the upper divided multiple of its own address, and the response signal is The center CP that detected the collision with the response signal of the terminal device of another station on the transmission path
In response to another inquiry from U, only the terminal device that has the transmission right by responding with the response window time corresponding to the specified address bit at the next position where the own address is divided into a plurality of times, sends the upstream data to the center CPU. A communication method characterized by transmitting.