JPH0362064B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field to which the Invention Pertains] The present invention relates to a local network communication system, and particularly to the CSMA/CD system (Carrier Sense
Related to communication methods using Multiple Access/Collision Detection methods).

[Description of prior art]

In recent years, local networks, which interconnect computers and data terminal equipment located in the same building, factory, or site, have been attracting attention as a basic means of promoting office automation and factory automation. , various methods have been proposed and put into practical use. One of the most famous methods is the CSMA/CD bus-type communication method, which is attracting attention as a simple and low-cost method. A typical example of this method is a local network called Ethernet, which was jointly developed and announced by DEC, Intel, and Xerox.

FIG. 1 shows the basic configuration of this system, and shows an example in which nodes A and B, which are separated by a distance, are accessing a bus # using a coaxial cable. Although several dozen nodes generally access the same bus, the figure shows a case where there are only two nodes A and B for simplicity.

Each node has a transmitter TX that receives the transmitted data SD and sends a signal to the coaxial cable, and a transmitter TX that receives the transmitted data SD and sends a signal to the coaxial cable.
A receiver RX that sends out the RD to the node terminal, a collision detection circuit D that detects a transmission/reception collision and sends a collision detection output CD to the node terminal, and a transmitter.
It consists of a tap T, which is the means to physically connect the TX and receiver RX to the coaxial cable.

FIG. 2 is a diagram for explaining an example of the operation of the communication system based on the present CSMA/CD system.

Each node usually intercepts communication between other nodes on the bus (Carrier Sense) at the beginning of its transmission,
Transmission starts only when it is confirmed that there is no communication. The transmission burst A ₁ from the node A and the transmission burst B ₁ from the node B in FIG. 2 are examples of the case where the transmission bursts are transmitted from each node in this manner and communication is successfully completed. However, even if a node starts transmitting after confirming that there is no communication, other nodes may also start transmitting in the same way, and in this case, collisions between transmission bursts occur on the same bus.

In the CSMA/CD system, a collision detection circuit D shown in FIG. 1 is provided for the purpose of detecting this collision. The specific collision detection method and its circuit configuration are well known to those skilled in the art, and further detailed description thereof will be omitted here.

When the collision detection output CD is output, the node that started transmitting immediately stops transmitting, and each node retransmits after a certain period of time, which is set by a random number for each node, has elapsed. Transmission burst A ₂ in Fig. 2,
C ₁ is an example of this.

As can be seen from the above explanation, the CSMA/CD method is characterized by a very simple system configuration, but on the other hand, due to its principle, the bus usage efficiency cannot be very high, and the CSMA/CD method cannot prevent interception and collisions. Detection (Carrier Sense & Collision
The disadvantage is that the bus speed itself cannot be very high (on the order of 10 Mbps) due to the inter-node propagation delay time in order to efficiently perform detection. Therefore, it can be said to be an extremely advantageous method when accommodating low-speed data terminals in a node.
This method is not suitable for accommodating high-speed data terminals, image terminals, or a large number of voice information terminals.

[Purpose of the invention]

An object of the present invention is to provide a local network communication method that can process large amounts of high-speed data while maintaining the simplicity of the system configuration of the CSAM/CD method.

[Key points of the invention]

The present invention provides a bus communication system comprising m communication buses (m is any integer greater than or equal to 2) and m communication nodes spaced apart from each other that commonly access the m communication buses. i-th (i is 1≦i
The communication bus (any integer ≥m) is used only for message transmission to the i-th communication node, and a specific communication node uses the i-th communication bus when starting transmission to the i-th communication node. It intercepts communication from other communication nodes to this i-th communication node, and if this i-th communication bus is in a non-communication state, it starts transmission via this communication bus, and this transmission happens to be on this communication bus. If it is detected that there is a collision with the communication from another communication node to this i-th communication node that started communication at the same time via The present invention is characterized in that if it is confirmed that the communication bus is in a non-communication state, retransmission is started, thereby enabling high-speed and large-capacity data processing.

[Explanation based on examples]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a system configuration diagram of the embodiment system of the present invention, in which buses #1, #2 to #m consisting of m (m is any integer of 2 or more) coaxial cables, and
A case is shown in which the communication node consists of two communication nodes.

Each communication node 1, 2 to m has buses #1, #2 to
Transmitters TX1, TX2 to TXm corresponding to #m,
Receivers RX1, RX2 to RXm are provided. Furthermore, each communication node has a changeover switch SW1 for selecting which destination node, that is, which bus, to send the transmission data SD to.
In conjunction with this, a switching circuit SW2 is provided for selecting the outputs of the receivers RX1, RX2 to RXm corresponding to the selected bus and guiding the selected outputs to the collision detection circuit D. Furthermore, the i-th (i is 1≦
The reception data line RD of the communication node i (any integer (i≧m)) is connected so that the output of the i-th receiver RXi of that node i, that is, the reception output from bus #i is output. has been done. Note that FIG. 3 shows an example where i is 1.

Next, the operation of the above-mentioned device will be explained.

For example, a case will be described in which communication node 1 attempts to start data transmission toward communication node i.

First, bus #i is selected by switching the switching circuits SW1 and SW2 in conjunction, and communication from other nodes to the i-th node i on this bus #i is intercepted. If it is in a non-communication state, it starts transmitting via this bus #i.

At this time, if there is a collision with the communication of another node on the bus #i, the collision detection circuit D detects the collision and immediately stops transmission, as in the case of the conventional device, and the transmission is stopped for a certain time preset by a random number for each node. Start retransmission after the elapsed time.

Note that the method of the present invention can of course be applied to transmission media other than coaxial cables. Furthermore, although this embodiment assumes that data is sent to the coaxial cable using a so-called baseband transmission method, it is not limited to this; for example, carrier wave modulation transmission method (for example, FM modulation method) By adopting N carrier waves with different frequencies and preparing N waves, it is possible to logically construct N buses on a single coaxial cable and apply the present invention.

[Explanation of effects]

As explained above, the present invention provides a local network capable of processing high-traffic messages that accommodates high-speed data terminals, image terminals, or a large number of voice information terminals by providing a plurality of buses. Communication method can be realized. Furthermore, the system of the present invention has the effect that the configuration of each communication node can be significantly simplified as a communication system that handles large amounts of high-speed data.

[Brief explanation of drawings]

Figure 1 is a system configuration diagram of the conventional CSMA/CD system. FIG. 2 is an explanatory diagram of the operation of the method shown in FIG. FIG. 3 is a system configuration diagram of an embodiment of the present invention. TX1, TX2 ~ TXm...Transmitter, RX1, RX
2~RXm...Receiver, D...Collision detection circuit.

Claims (1)

[Claims] 1. In a bus communication system comprising a communication bus and a plurality of communication nodes separated from each other that commonly access the communication bus, there are m communication buses (m is any number of 2 or more). (an integer of ) buses, and the plurality of communication nodes are composed of m communication nodes, and each of the communication nodes includes a transmitting means for communicating with one of the m buses, and comprising a receiving means for intercepting communications on each bus, and a collision detecting means for detecting a collision of communications on each bus; bus is used for message transmission to the i-th communication node, and each communication node
Intercepting communication from another communication node to the i-th communication node on the ith bus with the receiving means,
If this i-th bus is in a non-communication state, the above-mentioned transmitting means starts transmission via this bus; means for immediately stopping transmission when the collision detection means detects a collision with a communication to the i-th communication node; 1. A local network communication method, comprising means for confirming that the network has been retransmitted and then starting retransmission.