JPS61186045A - Access system in network system - Google Patents

Abstract

PURPOSE:To ensure the right of transmission to one node among plural nodes by transmitting a transmission right request signal to a bus for a time caused by generation of a random number when the bus is idle and judging whether the bus is idle or not just after the stop of transmission. CONSTITUTION:A node N trying transmission supervises at first the state of a bus 10 and sends the transmission right request signal to the bus 10 for a time caused by generation of a random number. The state of bus is checked just after the transmission of the transmission right request signal is stopped and when the bus is idle, it is judged that the transmission right is acquired to the own node to start data transmission. When the bus is not idle just after the transmission of the transmission right request signal is stopped, the procedure restores to the first procedure and it is awaited that the bus becomes idle. When the transmission right request signal is sent simultaneously from plural nodes, the timing of stopping the transmission of the transmission right request signal differs from each node and the node stopping the transmission finally detects 'idle bus just after stop of transmission' and obtains the transmission right.

Description

[Detailed Description of the Invention] A. Field of Industrial Application This invention relates to overconfidence systems, so-called local networks, used in fields such as office automation (OA) and factory automation (FA). This invention relates to an access method in a network system with a base structure.

86 SUMMARY OF THE INVENTION This invention provides a so-called local fake network COM
This is an access method that improves the shortcomings of the A/CD method, eliminates wasted time when a collision occurs, and quickly grants transmission rights to a certain node.

C0 Conventional technology In a network system where the line form is a bus structure,
The access method for each node to obtain transmission rights is as follows:
Typical examples are the C8MA/CD (carrier detection multiple access with sudden detection) method and the token passing method. In the C8MA/CD method, a node that wants to transmit starts data transmission after confirming that the line is free. At that time, if no data collision phenomenon with other nodes has occurred, data transmission continues, and if no collision is detected, data transmission is stopped. After stopping transmission, retransmission is performed after a certain random period of time according to a retransmission algorithm. Data transmission is successful! The above process is repeated until the transmission can be performed without collision.

In the token passing method, only one piece of special data called a token representing the transmission right is sent over the network, and only the node that has acquired the token can transmit data. After acquiring the token and transmitting the data, the node passes the token to the next node. The sending node simply passes the passed token to the next node.

Problems that the D0 invention seeks to solve: The CS MA/CD73 system is easy to control and can be realized at low cost, and has the advantage of short access waiting time and high efficiency when the communication load is low. There is.

However, when the load is high, the above-mentioned collisions occur frequently, the access waiting time becomes long, and stable fe@ transmission is not guaranteed. Ninth, O doesn't require very high speed.
Although it is practical for A, it is not suitable for FA, which requires high-speed response from the entire system. In the token passing method, each node always secures the transmission right t after a certain period of time. This has the advantage that stable fitting is not guaranteed even under high loads, and O
It can be applied regardless of whether it is for A or FA. but,
In order to sequentially send tokens to each node, it is necessary to set each node to which node to pass the token next, and there is also a function to monitor failure occurrences such as token loss or duplicate tokens, and failure recovery functions. is essential)
, the control is more complicated than the C8MA/CD force type, and the cost is higher. Also, when adding or removing nodes, the token t-
The order of passing must be reconfigured n#:1', which complicates the control.

This invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to provide a C8111! Same level as A/CD7j type or similar
In order to solve the O E0 problem tS, it is necessary to provide an access method that can be realized with simple control, reduces the average access waiting time, and allows efficient insertion even under high loads. Means: In the access method according to the present invention, a node that wishes to transmit accesses the network according to the following procedure.

First, monitor the status of the bus, and if it becomes vacant, iL
A transmission right request signal is sent to the bus only for a certain period of time depending on the number of occurrences. Immediately after stopping the transmission of this transmission right request signal, the bus status is checked, and if the bus is in an empty state, it is determined that the own node has been granted the transmission right, and data transmission is started.

If the bus is not free immediately after the transmission of the transmission right request signal is stopped, the process returns to the first step and waits until the bus becomes free.

20 Effects Also in the access method of the present invention, a collision phenomenon occurs in which transmission right request signals are simultaneously transmitted from a plurality of nodes.

However, the time during which each node continues to transmit the transmission right request signal is determined by random number generation and is different for each node.

Therefore, the timing at which each node stops transmitting the transmission right request signal is different, and the node that stops transmitting last detects that the transmission has stopped [the bus is empty afterward] and obtains the transmission right. .

G. Actual Example As shown in FIG. 1, in the network system according to the present invention, a bus 10 serving as a data transmission path is, for example, a coaxial cable with terminating resistors 12 and 12 connected to both ends. A large number of transmitting and receiving nodes N1 on the path IO
fJi is connected to the access method of this invention! 2
The explanation will be given according to the timing chart shown in the figure. First, the operation when one node Na transmits while all other nodes are not transmitting will be described. The node Na that is about to transmit confirms that the bus IO is free, and sends a transmission right request signal (hereinafter referred to as a busy signal) for a certain time t determined by the t-1 random number table. to bus 10. Once this busy signal is sent to the bus 10, the bus 10 is no longer in an idle state, and other nodes do not perform any transmission operations.

The sending node Na checks the state of the bus 10 immediately after stopping the transmission of the busy signal at time t1.

When the bus 10 becomes vacant by stopping the transmission of the busy signal, the node Na obtains the transmission right and immediately transmits data to the bus 10. Here, the confirmation time from stopping transmission of the busy signal to starting data transmission t is less than a predetermined reference time Δ, which is a very short time. Also, before transmitting the busy signal, the empty state of the bus [0 is checked, and the empty state at this time refers to an empty state that has continued for more than the above-mentioned time Δ.

Next, the operation when the two nodes Nb and Nc send busy signals to the bus IO almost simultaneously will be described. The times during which the nodes Nb and Nc transmit busy signals are each determined by a random number table, and in the example of FIG. 2, the busy signal transmitting time t2 of the node Nb is longer than the time t5 of the 7-day NC.

As a result, the node Nc suddenly stops transmitting the busy signal, but at this time the bus 10 is in a busy state because the node Nb continues to transmit the busy signal. To solve this problem, the node Nc says, "Bus 10 immediately after the busy signal transmission has stopped."
The busy signal is transmitted again after waiting for the bus IO to become empty (empty for more than Δ).

In short, when node Nb stops transmitting the busy signal, node Nc has already stopped transmitting, so bus lO
becomes vacant. Therefore, the node Nb detects the "vacant state of the bus 10 immediately after the stop of busy signal transmission" t-, and
It recognizes that it has obtained the right to transmit, and transmits data to the bus 10 after a short period of Δ after stopping transmission of the busy signal.

Even if a collision phenomenon occurs in this way, only one node will be given the right to transmit. This is the C8M A/
This is a feature of the present invention that is significantly different from the CD system. C8MA
In the /CD sword method, multiple nodes that have caused a collision all perform operations such as interrupting transmission and then retransmitting according to the retransmission algorithm. Therefore, according to Mr. 7i of the present invention, CS MA/CD
It can shorten the average access waiting time compared to the Near 3 type, and enables highly efficient and stable transmission even under high loads.

FIG. 3 shows the m ff fl J of the network interface thrown to each node when the method of the present invention is applied.

This network interface couples the aforementioned transmission bus 10 with a computer that processes transmitted and received data. The operation of this interface is controlled by a transfer controller a consisting of a microprocessor, a control memo IJ343 containing an FEPROM for storing its control program, and a RAM which serves as a working area.
It is managed centrally by. Well, this interface and the computer are connected via an input/output interface 39 that includes a buffer memory for transmitting and receiving data.

The transmitted data stored in the buffer of the input/output interface 39 is sent to the DMA controller when it is ready for transmission.
The transmission process between the serial and parallel mutual converters is then converted into serial data, and then the encoder/decoder 32 is used to encode the data, and then the transceiver 31 is transferred to the transmission bus 1.
Sent to 0.

Conversely, the signal on the transmission bus IO is received by the transceiver 31, encoded by the encoder/decoder 32, and
Convert to parallel data with serial/parallel converter 33 A, DMA
Controller that +! II is stored in the buffer of the input/output interface 39.

In order to carry out the above-described access method of the present invention, an access control circuit is provided after the bus monitoring circuit. When data is to be transmitted, first a transmission command is given from the transmission controller 37 to the access control circuit. In response to this, the access control circuit side checks whether the bus IO is in use or free based on the output of the bus monitoring circuit, and when it becomes free, activates the encoding section of the encoder/decoder 32 and the transceiver 31) transmitting section. and transmits the aforementioned busy signal to the bus 10. ft At the same time, a random timer function based on random number generation is activated, and the busy signal transmission operation is stopped after a certain period of time has elapsed. Immediately thereafter, the output of the bus monitoring circuit is checked to determine whether bus 0 is in an empty state. If the bus LO is empty, it notifies the transmission controller 37 that the right to transmit has been obtained, activates the transmitter of the transceiver 31 and the encoder of the encoder/decoder 32, and activates the input/output interface 39 as described above. The transmission data of is transmitted to bus IO.

The above access control can be performed using the transmission controller 37, but if high-speed transmission is desired, it is better to install a dedicated access control circuit 36 as in the example.

H1 Effects of the Invention As explained in detail above, in the access method in the network system according to the present invention, even if a plurality of nodes access the bus at the same time, one node among them can quickly secure the transmission right. This improves efficiency, especially under high loads. However, since the addition or removal of a node does not affect other nodes in any way, the system has high flexibility in changing the system, and there is no need for a dedicated control station to control access rights. In addition, complicated additional functions such as token disappearance, double talk/overlooking and recovery, as in the token pack sword style, are unnecessary.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a bus structure network that is the subject of this invention, FIG. 2 is a timing chart showing an example of the operation of the access method of this invention, and FIG. 3 is a configuration example of a network interface to which this invention is applied. FIG. N1~Ni-・-node, Na, Nb, NC・
-/-de, 10...Bus for fitting.

Claims (1)

[Claims] (1) An access method in a network system having a bus structure, in which a node attempting to transmit accesses the network according to the following steps a to d. a...Monitor the status of the bus and if it becomes empty,
A transmission right request signal is sent to the bus for a certain period of time based on random number generation. b...Immediately after stopping the transmission of the above transmission right request signal,
Determine whether the bus is vacant. c...If a vacant state of the bus is detected in step b, data transmission is immediately started. d...If the bus is not vacant in step b, return to step a and wait until the bus becomes vacant.