JPH0457144B2 - - Google Patents

Description

[Detailed Description of the Invention] <<Field of the Invention>> The present invention relates to a data communication system belonging to a local network that interconnects computer equipment distributed over a relatively narrow area, and in particular, the present invention relates to a data communication system belonging to a local network that interconnects computer equipment distributed in a relatively narrow area. Regarding the system that has.

<<Background of the Invention>> Recently, small-scale networks that interconnect computer equipment located within the same building, factory, or site, ie, local networks, have been actively developed.

Many currently known local networks employ a bus structure and employ CSMA/CD (carrier sense multiple access/collision detection) access control.

In addition, as an attempt to improve the basic CSMA/CD method, a system has been proposed in which packets are prioritized in order to speed up back-off processing when packet collisions occur. In this method, a preamble signal of a length corresponding to the priority is added to the beginning of each packet, and the longer the preamble, the higher the priority is given to the packet. If a collision occurs, the communication station with the shorter preamble will stop transmitting, but
The longer one continues to be sent and the data part is sent correctly.

However, the above-described priority control method has the disadvantage that since a preamble is added to the packet for priority control, the packet becomes redundant and communication efficiency is reduced.

≪Object of the invention≫ The object of the invention is to provide a data communication system that sets communication priorities for famous communication stations and that does not require deterioration of line time usage efficiency due to priority control. There is a particular thing.

<<Configuration and Effects of the Invention>> In order to achieve the above object, the data communication system of the present invention is configured as follows. In other words, it is a system in which one head-end device and a plurality of communication stations with determined priorities are connected to a frequency division multiplexed carrier bus, and data communication is performed between these communication stations. receiving/demodulating means for receiving and demodulating a signal outputted to the bus on a carrier wave with a frequency of 0;
A modulation/transmission means for outputting transmission data to the above-mentioned bus on a carrier wave of a specific frequency among frequencies 1 to n that differ for each priority, and when transmitting data by this modulation/transmission means, the transmission data and the above-mentioned reception / means for detecting a collision by comparing the data received by the demodulating means, and the head end device receives frequencies 1 to n from each of the communication stations.
n systems of receiving/demodulating means for receiving and demodulating the signal outputted to the bus on the carrier wave, and when only one system of these receiving/demodulating means is receiving the signal, outputs the received data. and a priority selection means for selecting and outputting the received data of the carrier wave frequency with the highest priority among them when multiple systems of the means are receiving signals at the same time; and modulation/transmission means for outputting to the bus on a carrier wave of zero.

According to this system, when a collision occurs in which multiple communication stations transmit at the same time, the priority control that operates so that the communication station with the highest priority can continue communication, does not involve any temporal redundancy. It can be achieved without any problems.

<<Description of Embodiments>> FIG. 1 shows the overall configuration of this system.
A large number of communication stations T1 to Tn are connected to the bus 1, and a head end device HE is provided at one end thereof. Bus 1 is multiplexed by frequency division, as explained below.

The communication station Ti (i = 1 to n) consists of a bandpass filter and an amplifier that receive a signal output from the head end device HE to the bus 1 on a carrier wave of frequency 0 (for example, 2-phase PSK modulation), as will be described later. It has a receiving circuit 2 and a demodulating circuit 3 that demodulates data RD from the received signal. The demodulated data RD is input to the transmission control circuit 4. Transmission control circuit 4
recognizes that bus 1 is free when the demodulated data RD is a series of “1”s (this is called all “1” data), and when the data RD is not all “1s”, the bus 1 is in use.

The communication station Ti desiring to transmit data checks the availability of the bus 1 as described above, and provides the transmission data SDi from the transmission control circuit 4 to the modulation circuit 5. The modulation circuit 5 performs two-phase PSK modulation on the carrier wave of frequency i determined by the priority assigned to the communication station Ti using data SDi, and transmits the modulated signal from an amplifier and a band filter tuned to frequency i. It is output to bus 1 by circuit 6.

In this embodiment, n communication stations T1 to Tn have n
It is assumed that the level priorities are assigned one level at a time. This priority order is distinguished by the frequency of the carrier wave of the signal output to the bus 1 by the modulation circuit 5 and transmission circuit 6 of each communication station Ti. Therefore, the carrier frequencies of the carrier signals of each communication station Ti in this embodiment are all different. Therefore, we set the carrier frequency of communication station Ti to i
It is expressed as Among the n types of frequencies 1 to n, 1 is the highest, 2 and 3 are lower in order, and n is the lowest. It is assumed that the priority order is ascending in order of carrier wave frequency. That is, the communication station T1 has the highest priority, and the communication station Tn has the lowest priority.

The head end device HE includes n systems of receiving circuits 71 to 7n that receive signals output from each communication station T1 to Tn onto a bus 1 on carrier waves of frequencies 1 to n, respectively, and data from each received signal.
It has demodulation circuits 81 to 8n that demodulate RD1 to RDn. The receiving circuit 7i consists of a bandpass filter tuned to the frequency i and an amplifier, and this amplifier also outputs a carrier detection signal CDi which becomes "1" when a carrier wave of the frequency i is present on the bus 1.
The carrier detection signal CDi from the reception circuit 7i and the reception data RDi output from the demodulation circuit 8i are input to the priority selection circuit 9 as a set of signals.

FIG. 2 shows a specific example of the priority selection circuit 9. This priority selection circuit 9 has an n-stage gate array.
AND1~ANDn, OR1~ORn, output gate G0, and gate G that inhibits output gate G0 when carrier detection signals CD1~CDn are all "0"
1.

Output signal of output gate G0 of priority selection circuit 9
SD becomes a modulation input of the modulation circuit 10. The modulation circuit 10 converts the carrier wave of frequency 0 into two phases with data SD.
PSK modulation. The modulated signal is transmitted to a carrier circuit 1 consisting of an amplifier and a bandpass filter tuned to frequency 0.
1 to bus 1. As mentioned above, each communication station Ti has a receiving circuit 2 and a demodulating circuit 3.
The signal output from the head end device HE to bus 1 is received and demodulated.

When none of the communication stations T1-Tn is transmitting, each carrier detection signal CD1-CDn in the head end device HE becomes "0".
In this case, the output SD of the priority selection circuit 9 is "1", and the modulation circuit 10 and carrier circuit 11 transmit a data string obtained by differentially encoding a series of "1"s onto a carrier wave with a frequency of 0 and send it to the bus. Output to 1. Each communication station Ti receives all "1" data from the head end device HE and recognizes that the bus 1 is in an empty state.

When a signal is output from one of the communication stations T1 to Tn to bus 1 on a carrier wave of frequency i, the receiving circuit 7i in the head end device HE
The signal is received/demodulated by demodulation circuit 8i, and demodulated data RDi and carrier detection signal CDi are input to priority selection circuit 9. In this case, as is clear from FIG. 2, the received data RDi from the demodulation circuit 8i appears in the output SD of the priority selection circuit 9, which becomes the modulation input of the modulation circuit 10. In other words, a signal transmitted from the communication station Ti to the bus 1 on a carrier wave of frequency i is received/demodulated by the head end device HE, and further, the received data RDi is converted into a carrier wave of frequency 0 by the functions of the modulation circuit 10 and the transmission circuit 11. It is then output to bus 1. This signal with carrier frequency 0 is transmitted to all communication stations T1 to T1 including transmitting station Ti.
Received on Tn.

In the communication station Ti that transmitted the data SDi, the transmitted data SDi is received/received by the receiving circuit 2 and the demodulating circuit 3.
Compare the demodulated received data RD, and if both data match with a certain time delay, bus 1
It is recognized that a collision has not occurred, and it is recognized that a collision has occurred when both data do not match.

Suppose that multiple communication stations, for example Ti and Tj, transmit signals to bus 1 at the same time. Then, the received data RDi is sent to the priority selection circuit 9 of the head end device HE.
and carrier detection signal CDi, and received data RDj
and carrier detection signal CDj are input. In this case, as is clear from the circuit of FIG. 2, the priority selection circuit 9 selects and outputs received data of a carrier frequency with a high priority. That is, the received data RDi transmitted from the communication station Ti on the carrier wave of i higher than j appears in the output SD of the priority selection circuit 9 and becomes the input of the modulation circuit 10.

In this way, even if multiple communication stations simultaneously send data to the head end device HE, the head end device HE selects only the data from the station with the highest priority among the received data and ignores the other data. Only the selected data is placed on a carrier wave with a frequency of 0 and output to bus 1. Therefore, the selected transmitting station uses the collision detection function described above to recognize that no collision has occurred. Furthermore, the transmitting stations that have not been selected recognize that a collision has occurred using the collision detection function described above, and interrupt transmission. In other words, even if a collision occurs, the transmitting station with the highest priority continues transmitting, and the transmitted data is correctly received by the other party.

In the above embodiments, the priority level is changed for each communication station, but the present invention is not limited to this. In other words, the number of priority levels may be smaller than the number of communication stations. In that case, a normal collision detection/backoff algorithm may be used for processing between a plurality of communication stations assigned the same level of priority.

Furthermore, the priority order of each communication station is set by the modulation circuit 5.
This is done by switching the frequency of the carrier wave given to the carrier wave and the tuning frequency number of the transmitting circuit 6. this is,
For example, it may be performed manually using a switch or the like, or it may be performed automatically using the transmission control circuit 4 or the host computer.

As a bus for frequency division multiplexing, transmission media such as coaxial cables, twisted pair wires, and wireless space can be used, and since it is a modulation type bus,
You can also use a power line.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a data communication system according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a specific example of the priority selection circuit 9 in FIG. T1 to Tn...Communication station, HE...Head end device, 1...Bus.

Claims (1)

[Claims] 1. A system in which one head-end device and a plurality of communication stations with determined priorities are connected to a frequency division multiplexed carrier bus, and data communication is performed between these communication stations, wherein the communication station is , receiving/demodulating means for receiving and demodulating the signal outputted from the head end device to the bus on a carrier wave of frequency 0; and a means for detecting a collision by comparing the transmitted data with data received by the receiving/demodulating means when transmitting data by the modulating/transmitting means. The head end device includes n systems of receiving/demodulating means for receiving and demodulating signals output from each of the communication stations onto the bus on carrier waves of frequencies 1 to n, and each of these receiving/demodulating means. When only one system is receiving a signal, outputs the received data, and when multiple systems of the means are simultaneously receiving signals, selects the received data of the carrier frequency with the highest priority among them. and a modulation/modulation unit that outputs the output data of the priority selection unit on a carrier wave with a frequency of 0 to the bus.
A data communication system comprising: a transmission means.