JPS61253944A - Method for controlling network circuit - Google Patents

Abstract

PURPOSE:To reduce the load of a host computer by using both a contention system and a poling system and controlling the switching of both the systems. CONSTITUTION:When receiving a communication request of which requesting terminal is unkown in the contention mode, the host computer inhibits respective terminals to generate successive communication requests. When the contention mode is turned to the poling mode, the host computer inquires respective terminals to check the terminal generating said request, and then executes communication with the terminal concerned. After poling the whole terminals, the host computer releases the whole terminals from the inhibition of the communication request generation and returns to the contention mode again. Consequently, it is unnecessary for each terminal to execute retransfer processing at the time of collision, reducing the load of the host computer.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a network system consisting of a computer and an intelligent terminal device, and particularly to communication line control that efficiently realizes communication line control of a network system with multi-drop type connections. Regarding the method.

[Background of the invention]

Although the contention method and the polling method are well known as general communication line control methods, there is no example of a control method that uses both in combination. This is a particularly close-up problem in line control of multi-drop network systems using a new communication circuit called R8-422, and we propose a new problem-solving method (CQ
Publication: Computer Data Communication Technology).

[Purpose of the invention]

An object of the present invention is to provide a communication line control method for a multi-drop network system, and to
An object of the present invention is to provide a communication line control method that makes it possible to reduce the load on a host computer by using a polling method in combination.

[Summary of the invention]

When the contention method is used for communication line control, high-response communication can be achieved if the transmission path is free, but as the number of network terminals or the amount of communication increases, communication collisions occur and retransmission processing becomes difficult. As a result, communication efficiency is significantly reduced. On the other hand, in the case of the polling method, the communication line is always controlled under the initiative of the host, so communication collisions are unlikely. However, in order to check whether there is communication by sequentially inquiring from the host to the terminal.

Even if a communication request is made on the terminal side, the terminal must wait until polling is performed, which poses a problem in responsiveness when a request occurs. In order to speed up the response, it is possible to speed up the polling cycle of the host, but this is not preferable because it increases the computer load on the host and interferes with the original processing operations of the host computer.

The present invention does not perform polling all the time and uses contention mode to accept communication requests quickly, but once a communication request is generated and accepted, it switches to polling mode, searches for the requesting terminal, and executes communication. do. Even if multiple simultaneous communication requests overlap, the system shifts to polling mode without processing retransmissions in contention mode, polls all terminals in turn, communicates with terminals that have requests, and polls all terminals. When finished, return to contention mode again. Since polling is performed only when there is a request, the computer load on the host hardly increases, and the response when a communication request occurs can be made sufficiently fast.

[Embodiments of the invention]

R3-232-C has been widely used in communication circuits in local area networks (LANs) due to its simplicity. However, the distance limitation (maximum 15 m) became an obstacle in network construction, and the system configuration was inefficient as it required the addition of omnidirectional OOSS (modulators and demodulators). As a solution to this distance limitation, R
8-422 has begun to be applied. With R8-422, if the host and terminal are connected one-on-one, the distance is simply about 1
There is no big advantage other than being able to extend it to -.

In the case of R8-422, a feature is that a plurality of terminals can be connected on one transmission path in a multi-drop manner. The topology of this network is shown in FIG.

As is obvious from Figure 1, the host computer and multiple terminals are connected by N on a single transmission path, so if a contention-based line control method is used for mutual communication, communication collisions will not occur. It is obvious that this will occur. Therefore,
A multi-drop type 1-to-N communication system such as R3-422 generally uses a polling method. In the polling method, the communication capability is determined by the polling cycle, and if faster response communication is desired, the polling cycle must be increased accordingly.

In this way, if the polling processing program is executed at a correspondingly high speed, the load on the host computer increases, which is a problem.

The present invention provides a means to solve such problems, and it is an object of the present invention to provide an inexpensive communication method that does not require dedicated hardware, has high response at the application program level, and has a low computer load. .

FIG. 2 is a diagram for explaining the present invention. The present invention is a communication method that combines the features of the contention method and the polling method.

Now, suppose that communication requests are issued from multiple terminal devices at the same time. Each terminal arbitrarily sends a communication request signal to the transmission path. In the case of a multi-drop transmission path, even if a request reaches the host, the host cannot know from which terminal the request is coming. In the general contention method, each terminal knows that someone other than itself is transmitting data to the transmission path, temporarily withdraws, and retransmits the data after an arbitrary period of time.

In the present invention, unlike a general contention method, each terminal does not perform retransmission processing regardless of a communication conflict, and each terminal enters a mode in which it waits for an instruction from the host. In other words, when the host receives a communication request from which it is unknown which terminal made the request, the next step is to prohibit each terminal from issuing further communication requests, and then switch to polling mode and make inquiries to each terminal in turn. After checking the terminal that issued the request, it communicates with the corresponding terminal. After polling all terminals in sequence, it issues a cancellation of communication request issuance prohibition to all terminals again, and then enters contention mode. Return to By doing this, the terminal does not need to perform retransmission processing in the event of a collision, and the host only needs to poll when requested by the terminal, so the computer load on the host is drastically reduced.

〔Effect of the invention〕

According to the present invention, polling is performed from the host only when there is a communication request, so the computer load on the host hardly increases, and one communication request is always accepted in contention mode, so quick response when a request occurs is achieved. can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the operation of the present invention. 1...Host computer, 2...Intelligent terminal station, 10th

Claims (1)

[Scope of Claims] 1. In a multi-drop type network system consisting of a host computer and a plurality of intelligent terminals, a contention method and a polling method are used in combination as the communication line control method, and control is performed by switching between them. Characteristic network line control method.