JPH04216235A - Collision detection type transmission system - Google Patents

Abstract

PURPOSE:To provide the collision detection type transmission system in which the scale of reception buffers of respective terminals can be minimized. CONSTITUTION:The transmission priority order is respectively set to respective terminals A, B and C connected to a bus (20). Data transmitted from these respective terminals contain transmission priority order information and when collision is caused, the transmission order is decided based on the transmission priority order. For the transmitting terminal completing already the transmission, the re-transmission to the same receiving terminal is inhibited until getting a response from the receiving terminal.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a collision detection type transmission system, in particular, a method for transmitting data by adding transmission priority information to transmission data.
The present invention relates to a collision detection type transmission system that determines transmission order according to transmission priority information when a collision occurs.

0002

2. Description of the Related Art With the advancement of communication technology, home control systems and the like have been introduced in homes. This home control system connects various load devices in a home via a common bus, and remotely or automatically controls each of the load devices via this bus.

[0003] In such home control systems, for example, CSMA/CD (Carrier
Sense Multiple Access
/Collision Detection) and the like are used. This CSMA/CD method is
Transmission priorities are determined in advance for each terminal (eg, load equipment, etc.) connected to a common bus, and transmission priority information is added to the communication data to be sent out before transmission. According to such a transmission method, when multiple pieces of transmitted data collide on the transmission path, the order of transmission is determined according to the transmission priority information included in the transmitted data, and smooth transmission without collisions is possible. Secured.

[0004] For reference, FIG. 5 shows the CSMA/
One frame of communication data (hereinafter referred to as a packet) in a transmission method such as the CD method is shown.

FIG. 5 shows the overall structure of a packet. First, transmission priority information (10) is added to the beginning. Specifically, this transmission priority information (10) is composed of a priority code (12) and a transmission source address (14). Note that the priority code (12) and the source address (14) each consist of, for example, one byte. Further, the destination address (16) is set next to the transmission priority information (10), and this destination address (16) is set next to the transmission priority information (10).
After 6), data such as a message to be sent is entered.

[0006] Here, when communication data collides on the bus, the transmission order is determined by the bit configuration of transmission priority information (10).

[0007] As described above, according to such a collision detection type transmission system, a single transmission path can be shared by multiple terminals without causing collisions, and a network that can perform smooth transmission with a simple configuration can be formed. It is possible to do so.

[0008]

[Problem to be Solved by the Invention] However, in this conventional collision detection type transmission system, a terminal with a low transmission priority requires a large data storage area in order to store transmission data from other terminals. There was a problem.

[0009] In other words, in a terminal with a low transmission priority, even though there is data to be transmitted from itself to the other terminal, since the bus is shared by multiple terminals,
The result is that transmission cannot be performed and only reception continues.

As a result, terminals with low transmission priority need to be equipped with many receive buffers for storing received data, and complex control is required to manage and control such large-scale receive buffers. (For the control of the reception buffer, see, for example, Japanese Patent Laid-Open No. 64-61147).

[0011] Therefore, in a home control system, for example, where a simple and inexpensive configuration is desired,
There has been a demand for a transmission system that can solve the above problems.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide a collision detection type transmission method that can prevent an increase in the accumulation of received data at a terminal with a low transmission priority in a collision detection type transmission system. The goal is to provide a transmission method.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a system in which a plurality of terminals each having a set transmission priority are connected to each other via a common transmission path, and transmission data from each terminal is If there is a collision on the transmission path, in a collision detection type transmission method that determines the transmission order according to the transmission priority information included in the transmission data, each terminal will continue to The feature is that a condition is set for not transmitting to the same terminal again.

[0014]

[Operation] According to the above configuration, the transmitting terminal is prohibited from transmitting to the same receiving terminal again until it receives a response from the receiving terminal.As a result, the receiving terminal has a higher transmission priority than the transmitting terminal. Therefore, it is possible to minimize the size of the reception buffer in terminals with low transmission priority.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred example of a transmission system to which the collision detection type transmission method according to the present invention is applied. Note that this system is based on the CSMA/CD method described above, and is suitable for application to, for example, a home control system in the home.

In the figure, a plurality of terminals, namely terminal A, terminal B, and terminal C, are connected to the bus (22). Here, a transmission priority is set for each terminal, and as shown in the figure, terminal A has the highest transmission priority,
Next is terminal B, and terminal C has the lowest transmission priority. Note that in this transmission method, transmission is performed using the packet shown in FIG. 5 as one frame of communication.

[0018] In the collision detection type transmission system according to the present invention, the receiving terminal that has transmitted the data does not transmit again to the same receiving terminal until a predetermined response is received from the receiving terminal to which the transmitted data was sent. It is characterized by not being carried out.

That is, for example, after terminal A sends data to terminal C, terminal A cannot send data to terminal C unless it receives communication data indicating a response from terminal C. be.

According to such a configuration, as shown in FIG. 1, each terminal only needs to determine the size of its reception buffer according to the number of terminals having a higher transmission priority than itself. be understood. To give a concrete example, suppose now,
If one reception buffer is required for one packet, terminal B has one reception buffer 22 for terminal A.
Similarly, terminal C only needs to have reception buffers (24) and (26) for terminal A and terminal B. This results in a significant reduction in cost compared to the conventional example. Further, there is an advantage that smooth transmission can be achieved while preventing collisions of transmitted data without intervening complicated communication control. Note that this also has the effect of reducing the size of the transmission buffer.

Next, a specific example of the collision detection type transmission system according to the present invention will be explained using FIGS. 2, 3, and 4.

A first example is shown in FIG. Time t
1, terminal A sends data (a) to terminal C.
Terminal B is about to send transmission data (b) to terminal C, and terminal C
is about to send transmission data (c) to terminal B.

When such conditions are set, each transmission data is sent to the bus (20) shown in FIG. 1, but in this case, the transmission data (a) from terminal A with a high transmission priority is As a result, only transmission data (a) is sent to terminal C. Note that each terminal shown in FIG. 1 uses a receiving circuit to feedback-monitor the transmission data that it attempts to send, and if there is a collision between the transmission data from the other terminal and its own transmission data, Collisions are now detected at the level above the bus. This is based on the CSMA/CD method. Here, the processing of transmission data (a) is t
It is performed between 1 and t3.

At time t2, terminal B is about to send transmission data (b) to terminal C, and terminal C
is about to send transmission data (c) to terminal B, but in this case, the transmission data (c) will be sent from terminal B to terminal C due to the transmission priority relationship. As a result, the reception buffer of terminal C stores the transmission data (a) from terminal A described above and the transmission data (b) from terminal B that was sent this time.

At time t3, since neither terminal A nor terminal B has received a response from terminal C, they are prohibited from transmitting the next transmission data. Therefore, terminal C can now send the transmission data (c) to terminal B, which it has not been able to send until now. And time t4
In , terminal B sends to terminal C a response to the transmission data (c) sent at time t3. At this time, terminal C attempts to send a response to terminal A's data (a) stored in the reception buffer, but due to the transmission priority relationship, the response to transmission data (c) from terminal B takes priority. . Then, at time t5,
A response to the data (a) sent at time t1 is sent from terminal C, whose turn has come for transmission, to terminal A.

Furthermore, at time t6, terminal C sends a response to the above data (b) to terminal B. Although not shown in the figure, even if transmission data arrives again from terminal A or terminal B at time t6, the reception buffer at terminal C is empty, so the reception data can be received without any problem. It becomes possible to process.

[0027] As described above, the transmitting terminal that has transmitted has the condition that it will not transmit again to the same receiving terminal until it receives a response from the receiving terminal that is its destination. This makes it possible to minimize the size of the reception buffer provided in each terminal, which in turn makes it possible to reduce costs.

Next, FIG. 3 shows a second example. At time t1, terminal A is about to send transmission data (a) to terminal B, terminal B is about to send transmission data (b) to terminal A, and further,
Terminal C is about to send transmission data (c) to terminal A.

[0029] In the case of setting such conditions, first, terminal A
Transmission data (a) is sent from terminal B to terminal B, and then transmission data (b) is sent from terminal B to terminal A. As a result, a response to data (b) is sent from terminal A to terminal B, and furthermore, terminal B sends the data (b) to terminal A.
A response to a) is sent.

In any of these processes, terminal C is not involved, and is placed in a transmission standby state due to the transmission priority. However, at time t5, transmission and reception between terminal A and terminal B are completed, so the transmission data (c) is sent from terminal C to terminal A, and furthermore, at time t6, the transmission data (c) is sent from terminal A to terminal C. A response to (c) will be sent.

A third example is shown in FIG. This third example is a slight modification of the second example, in which terminal C attempts to send transmission data (c) to terminal B at time t1. In this third example, the second
As in the example, at time t5, transmission data (c) is sent from terminal C to terminal B, and at time t6, terminal B
A response of data (c) is sent from terminal C to terminal C.

As can be understood from the examples above, according to the collision detection type transmission system according to the present invention, efficient transmission can be achieved by minimizing the size of the reception and transmission buffers. Is possible.

[0033]

[Effects of the Invention] As explained above, according to the collision detection type transmission system according to the present invention, the transmitting terminal transmitting
Since we decided not to transmit again to the same receiving terminal until we receive a response from the receiving terminal, we minimized the size of the receiving and transmitting buffers provided at each terminal to ensure smooth and reliable transmission. It is possible to achieve this.

Particularly in a home control system where the network size is relatively small, it is possible to provide a simple and highly reliable transmission system.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a system to which a collision detection type transmission method according to the present invention is applied.

FIG. 2 is an explanatory diagram showing a first example of transmission to which the collision detection type transmission method according to the present invention is applied.

FIG. 3 is an explanatory diagram showing a second example to which the collision detection type transmission method according to the present invention is applied.

FIG. 4 is an explanatory diagram showing a third example to which the collision detection type transmission method according to the present invention is applied.

FIG. 5 is an explanatory diagram showing an example of a packet that is one frame of communication data in a collision detection type transmission system.

[Explanation of symbols]

(10) Transmission priority information (20) Buses (22), (24), (26) Reception buffers A, B
,C terminal

Claims (1)

[Claims] Claim 1: When a plurality of terminals each having a set transmission priority are connected to each other via a common transmission path, and the transmission data from each terminal collides on the transmission path, the transmission priority is included in the transmission data. In a collision detection type transmission system that determines the transmission order according to transmission priority information, a condition has been established in which each terminal does not transmit to the same terminal again until it receives a response from the terminal to which it has transmitted. Collision detection type transmission method featuring: