JPS60219840A - Local network communication system - Google Patents

Abstract

PURPOSE:To decrease the probability of occurrence of collision of communication by preparing a channel according to the spread spectrum communication system where N-set of different code series is used and adopting the CSMA/CD system for the system to improve the bus efficiency. CONSTITUTION:A node A connected to a bus comprising coaxial cables by a tap T has a transmitter TX, receivers RX0, RX1, a collision detecting circuit D, a selection circuit L, a buffer memory circuit BM and switching circuits SW0, SW1. In starting data transmission, this node A intercepts other inter-node comminication, a channel in the non-communication state is selected and then the transmission is started.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a local network communication system, and relates to a special O8MA/CD system (Carrier Sense).
Multiple Accessloollision
L)ection method).

(Prior art and its problems) In recent years, office automation has become a local network that interconnects computers and data terminal equipment located in buildings, factories, and premises.

It is attracting attention as a basic means of promoting factory automation, and various methods have been proposed and put into practical use. Among them, the most famous method is O8MA.
/CD is a bus type communication method, and one representative example of this method is DEO.

E';F';f:yto (Ethernet
There is a local network called (registered trademark).

Figure 1 shows the basic configuration of this system.
Nodes A and B separated by distance on a bus using coaxial cables
Here is an example of access.

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 8D and sends a signal to the coaxial cable, a receiver 1 that takes in the information flowing on the coaxial cable to the node and sends it to the node terminal as received data RD, and a collision between transmission and reception. a collision detection circuit that detects and sends a collision detection output CD to the node terminal;
and a tap T which is a means for physically connecting the transmitter TX and receiver RX to the coaxial cable.

FIG. 2 is a diagram for explaining an example of the operation of a communication system based on the present 08 MA/CD system.

Each node usually intercepts communication between other nodes on the bus at the beginning of transmission (Carrier 5ense) L
/, start transmission only if it is confirmed that there is no communication. Transmission burst A from 7-door A in FIG.
, transmission berths Bl from node B are transmitted from each node in this manner, and communication is successfully completed. However, even if you confirm that there is no communication and start transmitting, other nodes may also start transmitting in the same way. In this case, collisions between transmission bursts on the same bus may occur. .

In the 08MA/CD method, this collision is detected (Co11i
Figure 1-
A collision detection circuit shown in this figure is provided. Since the specific collision detection method and its circuit configuration are well known to those skilled in the art, further detailed explanation 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, in FIG.

0 is an example of this.

As can be seen from the above explanation, the O8MA/CD method is characterized by a very simple system configuration, but on the other hand, due to the principle of the method, the efficiency of using the / and collision detection (Carri
er 5ense & Co11ision Dete
-ction), the bus speed itself cannot be set very high (on the order of 1 OMbps) due to the inter-node propagation delay time. Therefore, although this method is extremely advantageous when accommodating low-speed data terminals in a node, it is not suitable for accommodating high-speed data terminals, image terminals, or a large number of audio information terminals.

(Object of the invention) The present invention is capable of processing large amounts of high-speed data while maintaining the simplicity of the system configuration of the O8MA/CD method.
In addition, it is an object of the present invention to provide a local/network communication method that can improve bus usage efficiency. In a bus communication system with a plurality of communication nodes spaced apart from each other that have common access, each communication node is a node in multiple channels formed by spread spectrum communication using multiple pseudo-random sequences at the start of transmission. By performing spread spectrum demodulation and intercepting communication between channels using the pseudo-random sequence, one of the channels in the non-communication state ζ is selected, and the spectrum is changed using the pseudo-random sequence corresponding to the channel in the non-communication state. By performing spread modulation and starting data transmission, and comparing the transmitted data with the data passing through the channel on the simultaneous base bus, this transmission can be performed between other nodes that happened to start communication at almost the same time using the same channel. If a collision is detected, the transmission will be stopped immediately, and after a predetermined period of time, one of the channels in the non-communication state, including that channel, will be selected and retransmission will be started. It can provide formulas for local network communication methods that incorporate features.

(Example) - Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a system configuration diagram showing one embodiment of the present invention, and FIG. 4 is a diagram for explaining its operation.

In Fig. 3, each node is connected by a bus I/tap T consisting of a coaxial cable (the third
(Only node A is shown in the figure).

Node A has a transmitter TX and a receiver R,ll.

RXI, impulse detection circuit j3D, selection circuit, buffer memory circuit BM, and switching circuit swg.

swi.

The transmitter TX receives the transmission data 8D, performs spread spectrum modulation using two code sequences po and pi, and sends it to the bus E.
This is a transmitter that sends out this signal, and the code sequence p is on the bus.
Oζ thus forms the channel C)]0, and the code sequence p1 forms the channel CHI. The receivers XO and RX1 are receivers that perform spread spectrum demodulation using code sequences po and pl, respectively, and input the information flowing on the bus to the node terminals as received data RD. Send. The selection circuit is the transmission data S.
This circuit determines whether to send D through channel OHO or channel OHI, and the switching circuit 8WQ
to switch the code sequence to the transmitter TX. The collision detection circuit is a circuit that detects transmission collisions in each channel based on each code sequence f and sends a collision detection output CD to the node terminal l. The switching circuit SW1 connects the receivers RXO and R to detect the presence or absence of communication collision in each channel.
This is a switch for selectively guiding the output of XI to the collision detection circuit. The buffer memory circuit BM is used when there is damage data to that node from two channels at the same time.
This is a circuit for rubbing this so that one data line RDζ can be sent out.

Next, to explain the operation of this device, when node A wants to start data transmission, ζ channels OHU, C
It intercepts the communication (i!) between other nodes on HI, selects a channel that is in a non-communication state, and starts transmission.If both channels OHO and OH1 are in a non-communication state, a random number is Randomly select any of the 10,000 channels by f.

FIG. 4 is a diagram showing an example of the operation of this device.

In the figure, after nodes A and B have successfully sent out transmission bursts A, B1 through channel OHO, and node O has successfully sent out transmission burst co through channel 0)11, nodes A and C are sent at the same time - This shows a case where a collision occurs due to an attempt to start transmission via OHO on this channel.

In the conventional method shown in FIG. 1, in such a case, nodes A,
O immediately stops transmission and attempts retransmission via the bus after a certain period of time has elapsed, whereas in the method of the present invention, the channel selection circuit L+ shown in FIG. , one of the channels in the non-communication state is randomly selected and retransmission is started. In the example of FIG. 4, as a result, the transmission burst A of node A reselects channel OHI, and the transmission burst CI of node 0 reselects channel OHO and retransmits, indicating that the communication has been successfully completed. As can be seen from the explanations shown above, with this method, the probability that communications will collide on a certain channel is significantly reduced. Furthermore, even if a communication collision occurs, another channel is reselected, increasing the probability of successful retransmission.

Furthermore, the waiting time (backoff processing time) until retransmission is attempted after a collision can be reduced. For these reasons, N channels can carry much more traffic than N conventional systems. This will be explained below using a numerical example.

It is said that the upper limit of bus usage efficiency in the conventional 08MA/CD system is about η0 (maximum value)%. ), and let η be the upper limit of the individual channel efficiency in the case of this method.

In the conventional system, the probability that one bus is blocked when a node attempts to start communication is η0. When N channels are used in this method, the probability that all N channels are occupied is η9. Therefore, if the service standards for both are set equally, η0=η9. Now, assuming that t is η0=5096, when N=2, η=71%, and when N=3, it becomes 4279%. In other words, according to this method, when N channels using carrier waves with different frequencies are prepared, bus efficiency can be dramatically improved compared to the conventional system when N channels are prepared. In other words, the amount of data that can be processed can be dramatically increased.

The above comparison was based on the bus blockage rate, but it can also be proven that the probability of communication collisions occurring on a particular bus can be dramatically improved. However, here we will discuss the details (effects of the invention). As can be seen from the above explanation, according to this method, N channels using N spread spectrum communication (& method) using N different code sequences are prepared. By applying the /CD method, the conventional O8MA/CD system,%
Even compared to the case where N systems are prepared with C and N systems, bus efficiency can be dramatically improved and the probability of communication collisions can be reduced, making it possible to process large-scale and high-speed data.

[Brief explanation of drawings]

Fig. 1 is a system configuration diagram based on the conventional system f:iMA/CD system, Fig. 2 is an explanatory diagram of the operation of the system shown in Fig. 1, and Fig. 3 is a system configuration diagram of the first embodiment of the present invention. 4 shows an explanatory diagram of the operation of the method shown in FIG. 3. In the figure, A, B...... communication node, ) LX, RXO, R
XI...Receiver, TX...Transmitter,
D...Run collision detection circuit, BM...Buffer memory circuit, 8W0.8Wl...Switching circuit, L...Selection circuit, RD... ...Reception data signal line, 8D...Transmission data signal line, kL
8: transmission request signal line, O8: transmission enable signal line, pQ, pi: code series, respectively. Representative Patent Attorney Susumata Uchiita Figure 1 (' 5t) COF? OSDC, ORD Node A Node 8 Diagram Z Time →

Claims (1)

[Claims] (1) In a bus communication system that includes a communication bus and a plurality of communication nodes separated from each other that commonly access this communication bus, each communication node uses a plurality of pseudo-random sequences at the start of its transmission. spread spectrum communication
Intercepting inter-node communication in the plurality of channels formed by this by performing spread spectrum demodulation using the pseudo-random sequence - selecting one of the channels in the non-communication state from this and responding to the channel in the non-communication state Spread spectrum modulation is performed using a pseudo-random sequence to start transmitting data, and at the same time, by comparing the data passing through the channel on the bus and the transmitted data, it is possible to determine that this transmission happened to occur at approximately the same time using the same channel. If it detects a collision with the communication between other nodes that has started, it immediately stops the transmission, and after a predetermined period of time, selects one of the channels that are in the idle state again, including that channel. A local network communication method characterized by starting retransmission.