JPH05327727A - Multiplex transmission system - Google Patents

Abstract

PURPOSE:To provide a multiplex transmission system which reduces the spread of distribution of the time required for transmission of signals and also has the adaptability to the application field where the high real-time property is needed by approaching the sequenced transmission success to the generation sequence of signal. CONSTITUTION:A transmission line is divided into a reservation section where a signal transmitting sequence is decided and a transfer section where only a single message signal is transmitted and used cyclically between both sections. Then, a station where the signal to be transmitted during the pass of a pair of reservation and transfer sections is generated is unable to transmit a reservation signal until the transfer section ends at the relevant time point and transmits the reservation signal in the next reservation section. In the reservation section, the transmission of all reservation signals produced at the time point is completed with the use of a collation eliminating system of the conventional retransmission limiting CSMA/CD system. Each station counts the transmission success frequency of all reservation signals, the transmission success sequence of the reservation signals of its own station, and the emerging frequency of the transfer sections. Thus, the transfer section having the transmission right is autonomously decided at each station.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiplex transmission system, and more particularly to a multiplex transmission system with improved competition processing when retransmitting a transmission that collides on one transmission line.

[0002]

[Prior Art] CSMA / CD (Carrier Sense Multiple Acces
s with Collision Detection) method has been put to practical use. This is a LAN (Local Area Net
work) access method, and access control is performed by the following procedure.

When transmitting a signal (message), each station connected to the transmission line checks whether there is a signal on the transmission line, in other words, whether or not another station is actually transmitting a signal, and then the transmission line is transmitted. If no signal is detected at, the signal is transmitted. If a signal is detected on the transmission line, it means that the signal transmission by another station is actually being performed, and therefore the system waits until the signal transmission is completed.

The transmission procedure of the above-mentioned conventional multiplex transmission system is shown in the timing chart of FIG.

Specifically, as shown in FIG. 4 (a), when a message to be transmitted to the first station occurs at time T41, immediately if there is no other signal transmitting station, A message signal is sent. However, as shown in FIG. 4 (b), the message to be transmitted to the second station is T when the first station is transmitting the message signal as described above.
When it occurs at the time of 42, the second station transmits after waiting until the time of T43 when the transmission of the first station ends.

Further, when a signal is transmitted from a certain station by chance, if there are other stations simultaneously transmitting, the signals transmitted from a plurality of stations will collide on the transmission path.
In this case, the collision is detected from the signal waveform on the transmission path. When a collision is detected, the transmitting station retransmits after a waiting time determined by a predetermined algorithm has elapsed.

The transmission procedure in such a case is shown in the timing chart of FIG.

Specifically, as shown in FIG. 5 (a), at the time of T51, when a message to be transmitted to the first station is generated and an attempt is made to perform transmission, the same time as shown in FIG. As shown in b), when a message to be sent is generated in the second station and an attempt is made to send the message, both stations temporarily enter the standby state. In this case, the waiting time of the first station is the second
Assuming that the time is relatively shorter than that of the station, Fig. 5 (a)
As shown in, the retransmission request is first generated from the first station and the message signal is transmitted at time T52. At the time of T53 during the transmission period of the message signal of the first station, the second station
When the waiting time of the station ends, the second station issues a retransmission request.
The operation of the second station thereafter is similar to the procedure after the time point T42 shown in FIG. 4 (b) described above. After waiting until the time point T54 when the transmission of the first station is completed, the second station Transmission by the station takes place.

The above-mentioned waiting time is the standard CSMA / CD standard.
(IEEE 802.3) is determined by the following formula according to the number of collisions.

Standby time = slot time × r, where r: 0 is a uniform random number in the range of r ≦ 2 < ^{m −1}

Note that m = min (i, 10), i is the number of collisions, and the standard value of the slot time is 51.2 μsec.
In the case of 16 consecutive collisions, this signal transmission is aborted.

In such a conventional CSMA / CD system, as the traffic amount, that is, the communication amount increases, the probability of continuous collision increases, and the smaller the number of collisions, the smaller the number of collisions in the above-mentioned waiting time determination algorithm. The waiting time after occurrence of the collision is shortened, and the probability of successful signal transmission by retransmission is increased. Therefore, the spread of the time distribution required for signal transmission becomes large, and the order of signal generation and the order of successful transmission greatly differ.

In view of the problems in the conventional CSMA / CD system as described above, a multiplex transmission system called retransmission limited CSMA / CD system has been published by IEICE Technical Report IT-90-17 (1990-07). Has been proposed in.

In this retransmission limited CSMA / CD system, when a collision occurs, the stations not involved in the collision stop signal transmission until the successful transmission by the stations involved in the collision is completed, so that the signal generated earlier will be delayed. The probability of successful transmission before the generated signal can be increased, and the spread of the time distribution required for signal transmission is reduced.

A timing chart of FIG. 6 shows a transmission procedure by such a retransmission limited CSMA / CD system.

Specifically, in the retransmission limited CSMA / CD system,
As shown in FIGS. 6 (a) and 6 (b), when it is attempted to simultaneously transmit message signals from the first station and the second station at the time of T61, the above-mentioned FIG. ) Is performed in the same manner as the procedure shown in (4), the first station transmits from the time point T63 to the time point T65, and the second station issues a retransmission request at the time point T64. However, the third station, which was not involved in the collision at time T61, sends a message T65, even if it has a message to be transmitted, as shown in Fig. 6 (c).
Even if it occurs at the time of T62 until the time of, the transmission is stopped until the time of T65 when the transmission of the first station is completed. Then, the third station tries to transmit at time T65 when the transmission of the first station is stopped, but since the second station also holds the message to be transmitted, it is shown in Fig. 6 (b) and (c). As described above, a collision between the second station and the third station occurs at time T65.

After that, the same processing as described above is repeated, and the second and third stations transmit.

[0018]

[Problems to be Solved by the Invention] The above-mentioned retransmission restriction CSMA /
In the CD method, only one station can preferentially transmit after a collision occurs, and the number of past collisions and the signal generation order are not considered immediately after the point when one successful transmission is completed, and at that point in time. The stations having the signals to be transmitted have the same probability of successful transmission. Therefore, there is a possibility that the transmission of a specific station will be postponed later than the station that tried to transmit later, and as a result, it may be made to wait for a long period of time, and the time required for signal transmission is reduced. There is room for improvement regarding the breadth of the distribution.

As a proposal for this improvement, the above-mentioned retransmission restriction CSMA /
In the CD system, when a collision occurs, only the stations involved in the collision perform retransmission processing, and other stations may withhold transmission until all the stations involved in the first collision succeed in transmission.

Such a procedure is shown in the timing chart of FIG.

Specifically, as shown in FIGS. 7 (a) and 7 (b), as in the case of FIGS. 6 (a) and 6 (b) described above,
It is assumed that a collision occurs between the first station and the second station at time T71, and the transmission of the first station is completed at time T73. in this case,
As shown in Fig. 7 (c), T72 before the time of T73
Even if there is a message to be transmitted from the third station at the time of, the transmission of the second station involved in the collision at the time of T71 is prioritized. Then, the transmission of the second station is transmitted after T74.
When completed at the point of time, the transmission from the station (only the third station in the case of FIG. 7) having the message to be transmitted at this point is performed. That is, as shown in FIG. 7 (c), the first T
The transmission of the third station is stopped until the time of T74 when the transmissions of both the first and second stations involved in the collision are completed at the time of 71.

However, when the amount of traffic increases, the third station is actually in the period of the collision resolution processing, that is, in the above-mentioned case until the transmission of both the first and second stations involved in the collision is completed. Not only that, there is a high possibility that signals will be generated from many other stations. Therefore, a collision is likely to occur immediately after all the stations involved in the collision succeed in transmission, and there is a high possibility that many stations will participate in the collision. Although such a transmission process can improve the spread of the time distribution required for signal transmission, compared to the conventional CSMA / CD system, the extent thereof is not sufficient.

The present invention has been made in view of the above circumstances, and in the multiplex transmission system, by making the order of successful transmission closer to the order of signal generation than in the conventional method, the distribution of time required for signal transmission is distributed. It is an object of the present invention to provide a multiplex transmission system which has a small spread and is suitable for an application field requiring high real-time property.

[0024]

According to the method of the present invention, a transmission path is cycled into a reserved section for determining the transmission order and a transfer section for transmitting only one message signal, and a set of reserved sections is used. A station that has generated a signal to be transmitted during the transfer section cannot transmit the reservation signal until the transfer section at that time ends, and transmits the reservation signal in the next reservation section. In the reserved section, for example, the conventional CS
The MA / CD collision resolution method is used to complete the transmission of all reservation signals occurring at that time. Each station autonomously determines the transfer section in which each station has a transmission right by counting the number of successful transmissions of all reservation signals, the order of transmission success of the reservation signals of its own station, and the number of appearances of the transfer section. However,
Each station can reserve only one message signal.

[0025]

According to the multiplex transmission method of the present invention, the difference between the signal generation order and the transmission success order can be kept between stations in which a signal is generated during the passage of a set of reserved section and transfer section, and between different cycles. The order of successful transmission is the same as the order of occurrence between the stations where the signal is generated. As a result, it is possible to reduce the spread of the distribution of the time required for signal transmission, and it becomes possible to perform more real-time transmission.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments.

FIG. 1 is a timing chart showing a signal transmission state of each station of the multiplex transmission system according to the present invention.

In the multiplex transmission system of the present invention, the transmission path is divided into two sections, that is, a reserved section and a transfer section that appear alternately and used. However, when the system is started, it starts from the reserved section.

First, the processing of each station in the reserved section will be described with reference to the flowchart of FIG.

In the reserved section, only the station that is in the unreserved state at the start and has the message to be transmitted can transmit the reservation signal for transmitting the message. That is, each station checks the reservation status of its own station (step S1) and checks whether there is a message to be sent to its own station only when it is in the non-reserved status (step S2). Only if there is a reservation signal transmission processing is performed (step S3).

The length of the reserved signal is 512 bits, which is the minimum value allowed by the CSMA / CD system. The reservation signal transmission process is performed using the conventional CSMA / CD method.

The station transmitting the reservation signal is cycle 0 in FIG.
The transmission of the reservation signal is started at the same time as the start of the reservation section 0. At this time, as shown in FIGS. 1 (a) and 1 (b),
Collisions occur when a plurality of stations, the first station and the second station, transmit reservation signals. When each station that transmits the reservation signal detects this collision, each station waits for a waiting time determined according to a predetermined algorithm, and then attempts retransmission. In order to resolve this collision at high speed, the above-mentioned retransmission limit CSMA / CD
The adoption of the method is effective. However, if one station, for example, the second station as shown in Fig. 1 (b), succeeds in transmitting the reservation signal by retransmission after the reservation signal collision occurs, immediately after that, the reservation signal is still transmitted. The station that has not succeeded in (1st station) starts retransmission of the reservation signal and succeeds in transmitting the reservation signal. If a plurality of stations transmit the reservation signal again at this point, a collision occurs again, and the collision is resolved by the same procedure as described above.

By repeating the above procedure, all the reservation signals generated during the reservation section 0 of cycle 0 are successfully transmitted. In the example shown in FIG. 1, the second station acquires the right to use transfer section 0 of cycle 0, and the first station acquires the right to use transfer section 1 of cycle 1. After this, the transmission line is in a non-signal state. Each station monitors the non-signal state of this transmission line, and when the time exceeds the round-trip propagation delay time, the reserved section 0 of cycle 0 ends.

However, if two reserved signals are successfully transmitted in succession during the reserved section, it can be determined that all reserved signals have been successfully transmitted. Therefore, even if the reserved section is ended without monitoring the no-signal state. Good. Further, in the reserved section, each station increments the number of reservations stored internally by detecting the successful transmission of the reservation signal of another station, and if the reservation signal of its own station is successfully transmitted, the reservation at that time is made. The number is stored as the reservation order of the own station, and the state of the own station is set as reserved (step S
4) Wait for the end of the reserved section (step S5). In addition,
The initial value of the reservation number is "0".

Next, the processing of each station in the transfer section will be described with reference to the flowchart of FIG.

When moving to the transfer section 0 of cycle 0, each station checks the reservation status of its own station (step S11). If it is already reserved, check the reservation order of your own station (step S12),
If the value is "0", the message transmission process of the own station is performed (step S14), and then the state of the own station is set to the unreserved state (step S14). In the example of FIG. 1, since the second station has acquired the right to use the transfer section 0 of cycle 0, as shown in FIG. 1, the second station sends a message in the transfer section 0 of cycle 0. To do.

If the value of the reservation order of the own station is other than "0", it is judged that the other station has the right to use the transfer section at that time (step S12). Is decremented by "1" (steps S15, S16). And wait until the successful transmission of the signal of another station is observed
(Step S17).

If the reservation state of the own station is not reserved at the time of moving to the transfer section (step S11), the number of reservations is checked (step S18). If the value is "0", the transfer section ends.
If the value of the reservation number is other than "0", the reservation number of the own station is "1"
It decrements (step S16) and waits until the successful transmission of the signal of another station is observed (step S17). When one of the signals of the own station or another station is successfully transmitted, the transfer section is ended at that point and the procedure returns to the reserved section.

Thereafter, in the reserved section 1 of cycle 1, as shown in FIGS. 1 (c) and 1 (d), when the third and fourth stations generate the reservation signal, the above-mentioned first and first stations are generated. The same processing is performed as in the case of two stations, the third station acquires the right to use the transfer section 2 of cycle 2, the fourth station then acquires the right to use the transfer section 3 of cycle 3, and the reserved section 1 ends. To do.

In the transfer section 1 of cycle 1, as described above, since the first station has already acquired the usage right in the reserved section 0 of cycle 0, the first station sends a message.

In the next reserved section 2 of cycle 2,
As shown in FIG. 1 (b), if only the second station generates the reservation signal, the second station is immediately given the right to use the transfer section 4 of cycle 4 and becomes the transfer section 2. In the transfer section 2, since the third station has already acquired the usage right in the reserved section 1 of the cycle 1 as described above, the third station transmits the message.

In this way, each station sequentially reserves the right to use the transfer section, and the message is transmitted.

[0043]

As described in detail above, according to the present invention,
Solved the problem that the difference between the signal generation order and the successful transmission order could be kept within a limited range, and that the transmission time required by some stations could be extremely long during high traffic with the conventional method. However, the adaptability to the application field that requires high real-time property is also increased.

[Brief description of drawings]

FIG. 1 is a timing chart showing a signal transmission state of each station of the multiplex transmission system according to the present invention.

FIG. 2 is a flowchart showing processing of each station in a reserved section.

FIG. 3 is a flowchart showing processing of each station in a transfer section.

FIG. 4 is a timing chart showing a transmission procedure of a conventional multiplex transmission system.

FIG. 5 is a timing chart showing a transmission procedure of a conventional multiplex transmission system.

FIG. 6 is a timing chart showing a transmission procedure of a conventional multiplex transmission system.

FIG. 7 is a timing chart showing a transmission procedure of a conventional multiplex transmission system.

Claims (1)

[Claims] 1. A transmission path is divided into a first section and a second section that follows and is repeatedly used, and in the first section, each of a plurality of stations connected to the transmission section sends a message. At the time of transmission, if the transmission path is free, it is immediately sent as a new message successfully.If the transmission path is being used by another station, it waits until the successful transmission is completed, and it is sent simultaneously with other stations. If a collision occurs, the data signal to be transmitted is held at the start point of the first section by the multiplex transmission method in which after waiting for a waiting time determined according to a predetermined algorithm, the retransmission message is successfully transmitted. Reservation signal messages are transmitted until all stations succeed in transmission, and each station acquires the transmission right in the order in which the reservation signal is successfully transmitted. In the second section, the station that acquires the transmission right receives the transmission right. A multiplex transmission method characterized in that data signals are transmitted to each station in sequence.