JPH0457146B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a communication system using a U-shaped bus, and more particularly, the present invention relates to a communication system using a U-shaped bus, and in particular, to determine whether or not there is a collision based on the time difference between a transmitted signal and a received signal at each transmission terminal, and to give priority to the collision. The present invention relates to a communication system that performs processing.

(Background of the Invention) Conventionally, the so-called carrier sensed multiple access/collision bidet (CSMA/CD) method has been known as an access control method from each transmission terminal in a bus-type local area network (LAN). There is. This method detects an empty line before transmitting, and if transmissions from multiple terminals collide, it waits for a predetermined period of time before transmitting again. An empty line is detected by detecting a carrier signal on the line. This can be done by detecting a pulse signal or by detecting a pulse signal. Also,
With priority, which is an improved version of the CSMA/CD method
In the CSMA/CD system, each terminal is prioritized, and in the event of a collision, the terminal with a higher priority transmits. Furthermore, a CSMA/CD system with ACK has been proposed to prevent collisions of reception confirmation packets, ie, ACK packets, sent back from the receiving circuits of each terminal.

However, in all of the above methods, when the communication line is used infrequently and under low load, the probability of collisions and re-collisions is low and the transmission efficiency is good, but when the load is high, re-collisions increase and the throughput time becomes very high. The problem was that it was long. In order to eliminate these inconveniences, a re-collision avoidance CSMA/CD method that uses directional accessors for linking and coupling has been proposed, but this requires the use of directional accessors, which complicates the hardware. Moreover, since it is necessary to transmit reserved pulses in the conflict resolution mode, there is a problem that control becomes complicated.

(Object of the Invention) In view of the problems with the conventional type described above, the object of the present invention is to accurately avoid collisions and re-collisions using simple hardware and control procedures in a communication system using a U-shaped bus. The purpose of the present invention is to reduce waiting time when a collision occurs, improve communication efficiency, and ensure equality among transmission terminals.

Note that in this specification, a U-shaped bus refers to a "data transmission bus in which the direction of data transmission is reversed from the downward direction to the upward direction at the turning point, and the transmitted data in the downward direction and the upward direction are separated." means. Therefore, both of the devices shown in FIGS. 1a and 1b of this specification correspond to the U-shaped bus referred to herein.

(Configuration and Effects of the Invention) The present invention detects the presence or absence of a collision and processes it with priority by measuring the time difference between the transmission start time and the reception start time at each terminal in a communication system using a U-shaped bus. This concept is based on the idea that collisions and re-collisions can be accurately avoided with a simple configuration, reducing waiting time in the event of a collision and reducing line usage. It becomes possible to improve efficiency and ensure equality among each terminal.

(Embodiments of the Invention) Hereinafter, embodiments of the present invention will be explained based on the ground.
FIGS. 1a and 1b show a schematic configuration of a communication system according to an embodiment of the present invention. In FIG. 1a, a U-shaped bus 1 has multiple transmission terminals 2-1, 2-2.
-2,...,2-n are connected. The transmitting circuit of each transmission terminal 2-1, 2-2, . . . 2-n is connected upstream of the turning point of the U-shaped bus 1, and the receiving circuit is connected downstream. Further, the upstream end and the downstream end of the U-shaped bus 1 are terminated by termination circuits 3-1 and 3-2, respectively. In such a system, transmission data output from the transmission circuit of one of the transmission terminals is transmitted from the upstream of the U-shaped bus 1 to the downstream via the turning point, and is input to the reception circuit of the other transmission terminal. Communication is thereby performed between each transmission terminal.

FIG. 1b shows another embodiment of the U-shaped bus, in which the U-shaped bus is constructed using a single bus 4. In FIG. A head end 5 is connected to one end of the bus 4, and the other end is terminated by a termination circuit 3. The bus 4 also includes a plurality of transmission terminals 6-
1, 6-2, . . . 6-n are connected. In this system, transmission data from one of the transmission terminals is modulated by, for example, a high-frequency carrier wave and sent out onto the bus 4, and is frequency-converted into a lower frequency signal at the head end 5 and transmitted on the bus 4 in the opposite direction. and received by one of the transmission terminals. Each transmission terminal has a filter for separating the transmitted signal and the received signal, and together with the head end 5 provided on the bus 4, the single bus operates as a U-shaped bus. There is.

FIG. 2 shows a schematic configuration of a transmission terminal used in a communication system according to an embodiment of the present invention.
The transmission terminal in the figure is composed of a processor 8, a transmission register 9, a reception register 10, a time difference measurement circuit 11, a transmission circuit 12, a reception circuit 13, and the like. The output of the transmitting circuit 12 is connected, for example, to an upstream node of the U-shaped bus 1 in FIG. 1a, and the input of the receiving circuit 13 is connected to a downstream node of the U-shaped bus 1.

In the transmission terminal shown in FIG. 2, transmission data from processor 8 is sent via transmission register 10 and transmission circuit 12 to the upstream side of the U-shaped bus.
Further, a signal received from the downstream side of the U-shaped bus is input to the reception register 10 via the reception circuit 13 and taken into the processor 8. Further, the time difference measurement circuit 11 measures the time difference from the start of transmission to the start of reception and reports it to the processor 8, and the processor 8 performs collision detection etc. based on this time difference data.

Next, the collision detection method in the transmission terminal of FIG. 2 will be explained with reference to FIGS. 3a and 3b. Processor 8 monitors the data string from reception register 10 in response to a transmission request, and when it detects that the line is vacant, it starts data transmission via transmission register 9 and activates time difference measurement circuit 11. The time difference measuring circuit measures the time from the start of transmission to the start of reception and notifies the processor 8 of the time. The processor 8 compares the transmitted data and the received data when the time difference is notified, and if the transmitted and received data completely match, it stores the time difference and uses it for determination. This time difference corresponds to the propagation time T of the signal from the transmitting circuit to the receiving circuit via the U-shaped bus within the same transmission terminal. That is, as shown in FIG. 3a, transmission is started after the line idle signal becomes high level, but the start of transmission causes the time counter in the time difference measuring circuit 11 to start counting, and the start of reception causes the counting of the time difference measurement circuit 11 to start counting. Counting of the time counter is stopped. In this way, the time difference from the start of transmission to the start of reception is measured. If this time difference is greater than the previously stored time T, it is determined that there is no collision, and conversely, as shown in Figure 3b, if this time is shorter than the aforementioned time T, there is a collision. transmission is immediately interrupted.

FIG. 4 shows details of the transmission procedure at each transmission terminal. As shown in the figure, first, the transmitting flag is checked to determine whether there is a transmission request. If the transmitting flag is not on, it is determined whether the receiving flag is on, and if the receiving flag is not on, it is checked whether the line is idle. This line availability check is determined based on, for example, whether a state in which there is no carrier wave continues for a predetermined period of time or more, or whether data 1 continues for a predetermined number N or more. If the line is empty, the receiving flag is turned off and it is determined whether there is a transmission request.
If there is a request to send, turn on the sending flag,
Then, after turning off the transmission success flag, the process returns to the starting point. In determining whether the line is free or not, if the line is not free, the frame start flag is checked, and if the frame start flag is on, the receiving flag is turned on. Further, in the initial processing, if the transmitting flag is not on and the receiving flag is on, the received data is stored character by character and the frame end flag is checked. If the frame end flag is on, check whether the received data is the own received data using address data etc. in the received data, and if it is the own data, store it in a predetermined storage area and If it is not data, the received data is discarded. Then, after turning off the receiving flag, the process returns to the starting point. In the initial processing from the start point, if the sending flag is on, the sending start flag is turned on and the sending data increment counter is preset. Furthermore, after presetting a response waiting timer, the process moves to data transmission processing. In the data transmission process, one unit of data is transmitted, a response wait timer is incremented, and a data counter is incremented, and then the presence or absence of received data is determined. If there is no received data, the next unit of data is transmitted using the same procedure. If there is received data, it is determined whether the response wait timer is before time-up.
If the response wait timer is before time-up,
As mentioned above, since the time difference from the start of transmission to the start of reception is smaller than the predetermined value T, it is determined that a collision has occurred, and both the transmitting flag and the transmitting start flag are turned off and the process returns to the starting point. If the response wait timer is not before time-up, it is determined that there is no collision, and the transmitted and received data are verified.
If the transmitted and received data match, the data transmission process is continued and the data counter is incremented. Then, it is determined whether transmission has been completed up to the last data, and if it has been completed, the transmitted and received data are compared to determine whether or not they match up to the last data. If the data matches until the last data, turn on the transmission success flag, set the waiting time, and then
Both the transmitting flag and the transmitting start flag are turned off and the process returns to the starting point. This waiting time is set in order to ensure equality among the transmission terminals by setting a certain transmission request suspension requirement after one transmission terminal has successfully transmitted. In addition, in such transmission processing, as a result of checking the transmitted and received data,
If they do not match, it is assumed that there has been a collision, and the priority claim preamble is transmitted for a predetermined period of time, and then the transmission process is executed from the beginning. This priority claim preamble is transmitted during the maximum propagation delay time of the U-shaped bus from the start of reception.

Next, the operation of the communication system of the present invention will be explained in comparison with the conventional type using time charts shown in FIGS. 5a and 5b. FIG. 5a shows a transmission procedure in a conventional communication system. As shown in the figure, terminal N3 first performs transmission, and the transmission data is transmitted to terminal N1 via a turning point. No collision occurred at this time. Next, if terminal N4 starts transmitting and terminal N1 starts transmitting almost at the same time, terminal N1 detects the collision when the transmitted data of terminal N4 reaches terminal N1 via the turning point, and cancels its own transmission. After data is received, it waits for an arbitrary time t1. Furthermore, the terminal N4 detects a collision at the time when the data transmitted by the terminal N1 is received, and waits for an arbitrary time t2 after the end of receiving the data transmitted by itself. Terminal N1 then starts transmitting after time t1 and completes playback without collisions, and terminal N2, for example, receives the data. Terminal N
4 checks whether there is a line available to start transmission after the waiting time t2, since the terminal N1 is transmitting, so it waits until the terminal N1 finishes transmitting and then retransmits after the waiting time t3. in this way,
In the conventional system, there was a disadvantage that the dead time t4, t3, etc. in the event of a collision etc. became considerably large and the transmission efficiency deteriorated.

FIG. 5b shows a transmission procedure in a communication system according to an embodiment of the present invention. As shown in the figure, first, terminal N3 starts transmission, and transmission is performed up to terminal N1 without causing any collision. In this case, processing is performed in the same way as standard CSMA/CD, all nodes N1 to N5 receive normal data, and only N1, which is the receiving terminal, takes in the data. Next, when terminal N4 and terminal N1 start transmission at the same time, terminal N4, which is closer to the turning point, retransmits the data t5 hours after starting reception. At this time, a preamble is sent between detection of collision and retransmission. Terminal N1 transmits data without causing a collision after time t6 has elapsed since the collision was detected and the time for receiving the data transmitted by terminal N4 has elapsed. That is, in the communication system according to the present invention, when there is no collision condition, standard CSMA/
It operates in the same way as CD, and even if a collision condition occurs, only the maximum propagation delay time is wasted during one communication. Furthermore, even if, for example, all terminals issue transmission requests at the same time, communication is performed sequentially starting from the one closest to the return point, so the maximum value of throughput becomes clear and transmission efficiency improves.
Furthermore, since a U-shaped bus is used, there is no need to limit the minimum value of the bucket.

[Brief explanation of the drawing]

1A and 1B are block circuit diagrams showing the general configuration of a communication system according to an embodiment of the present invention, and FIG. 2 shows the configuration of each transmission terminal used in the communication system according to an embodiment of the present invention. 3A and 3B are time charts for explaining the transmission process in the transmission terminal of FIG. 2, and FIG. 4 is a block circuit diagram for explaining the transmission procedure in the communication system according to one embodiment of the present invention. The flowchart and FIGS. 5a and 5b are explanatory diagrams for explaining the transmission procedure of a communication system according to an embodiment of the present invention in comparison with a conventional type. 1: U-shaped bus, 2-1, 2-2,..., 2-n,
6-1, 6-2,..., 6-n: transmission terminal, 3-
1, 3-2, 3: Termination circuit, 4: Bus, 5: Head end, 8: Processor, 9: Transmission register,
10: Reception register, 11: Time difference measurement circuit, 1
2: Transmission circuit, 13: Receiving circuit.

Claims (1)

[Claims] 1. In a communication system in which multiple transmission terminals are connected to a U-shaped bus, and the transmitting circuit of the same transmission terminal is connected upstream from the turning point of the U-shaped bus, and the receiving circuit is connected downstream, each transmission terminal has its own A means for detecting a collision between transmitted data and received data and a means for measuring the time from the start of transmission to the start of reception are provided, and if there is a transmission request, the line is detected to be free and transmission is started, and the collision is detected. If the collision is not detected, continue the transmission, and if the collision is detected, if the detection timing is before the start of normal reception on the own side, immediately stop the transmission and wait for the next free line, and the detection timing is before the start of normal reception on the own side. If the time has elapsed, the transmission data is transmitted after transmitting the priority claim preamble for a predetermined period of time, and after the transmission is completed, the next A communication system using a U-shaped bus characterized by transmitting data.