JPH0568902B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to broadcast communications in local area networks. In particular, it relates to a retransmission system for broadcast communication in a loop (ring) network.

[Summary] The present invention is a broadcast communication system that transmits and receives command frames and data frames sequentially in a loop-shaped local area network. If no round frame is detected within the time, the broadcast frame is retransmitted at the time interval in which the frame goes around the loop, and after receiving the first broadcast frame, the receiving side receives the next broadcast frame. By ignoring retransmitted frames received within the waiting time as redundant transmissions, retransmission can be performed without double reception in broadcast communications.

[Conventional technology]

As a communication method in a local area network, a method in which one station transmits the same data frame to all other stations at the same time is called broadcast communication, but since it is generally difficult to use a response confirmation method in similar communication, There was a problem with the retransmission timing on the transmitting station side and the confirmation of the retransmitted frame on the receiving station side, so retransmission was not performed.

[Problem that the invention seeks to solve]

However, in such conventional broadcast communication, response confirmation and retransmission are not performed, so if there is an intermittent failure in the transmission path or receiving station side, or if the load on the receiving station side due to individual communication is large, However, broadcast frames were sometimes not received, resulting in low communication reliability.

SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned drawbacks, and an object of the present invention is to provide a broadcast communication system that performs retransmission without double reception in broadcast communication in a loop network.

[Means for solving problems]

The present invention includes a plurality of stations connected through a loop network and sequentially transmitting and receiving broadcast frames including command frames and data frames;
It is equipped with a host processor that is connected to each of the plurality of stations and controls the broadcast communication, and before transmitting the broadcast data frame, it sends a broadcast command frame indicating that the broadcast data frame will be transferred. In the broadcast communication method for forwarding, each host processor has a first timer means that is activated when a broadcast frame is transmitted and monitors one cycle of the broadcast frame, and a first timer means that is activated when the broadcast frame is transmitted and monitors the next broadcast frame. a second timer means for waiting for the transmission of a frame, activated by the timeout of the first timer means,
Retransmission means for retransmitting the broadcast frame within the timer time of the second timer means, and third timer means that is activated upon reception of the broadcast frame, inhibits new individual transmission, and waits for the next broadcast frame. and ignoring means that is activated when a broadcast frame is received, and ignores the second and subsequent broadcast frames received by retransmission as redundant transmissions while the third timer means is in operation. do.

[Effect]

In the present invention, on the transmitting side, when transmitting a broadcast frame, the first timer means for cycle monitoring and the second timer means for waiting for the transmission of the next broadcast frame are activated, and when the first timer means times out, the transmission is retransmitted. and retransmission is performed within the timer time of the second timer means. On the receiving side, when receiving a broadcast frame, the third timer means and ignore means are activated, and while the third timer means is operating in the ignore means, the second and subsequent broadcast frames received by retransmission are treated as redundant transmissions. Ignoring it allows retransmission without double reception in broadcast communication.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a broadcast communication device according to an embodiment of the present invention. In Fig. 1, stations A, B,
Stations C and D are connected via a loop local area network, and stations A, B, C, and D are connected to host processors W, are sent and received in sequence.

The operation of the broadcast communication device having such a configuration will be explained.

FIG. 3 shows packet frames transmitted and received between stations in the loop network of the broadcast communication apparatus of the present invention. A packet frame has a time filler TF that fills the space between frames, a delimiter F that indicates the start of the frame, a destination address DA, a source address SA,
Frame type (token, response, information) LC, command frame or data frame distinction CI,
Original transfer information I, frame check sequence
It is composed of fields FCS, delimiter F indicating the end of a frame, and time film TF filling the space between frames.

When the destination address DA field is "FF", the frame is particularly called a broadcast frame, and each receiving station on the loop network is required to perform reception and relay operations.

FIG. 1 is a block diagram of a broadcast communication apparatus according to the present invention, and shows a loop-like network when mutual communication is performed using the packet frame shown in FIG. Host processor W, X,
Y and Z perform data transmission and reception operations with each other via stations A, B, C, and D connected to loop-shaped transmission lines, respectively. A feature of the loop-shaped transmission path is that when a broadcast frame from the host processor W is transmitted from station A, it is transferred in a fixed direction to stations B, C, and D, and each station performs a receiving operation and a relay operation. ,
The broadcast frame is sent to each host processor
Transferred to Y and Z. The broadcast frame relayed by station D makes a round and returns to station A again. Here, station A erases this broadcast communication frame by stopping the relay operation at the same time as detecting this broadcast frame.

At station A, a one-cycle check is possible by starting a one-cycle monitoring timer at the start of transmission, and stopping the monitoring timer when one cycle frame is detected. When a timeout occurs, it is assumed that an intermittent failure has occurred on the transmission path, and playback is started. Use as a trigger.

FIG. 2 is a block diagram of a monitoring timer for controlling a transmitting station broadcast frame in the broadcast communication apparatus of the present invention. The flip-flop 25 is controlled by the transmission activation signal 34 inputted to the J input of the flip-flop 25, and the one-cycle monitoring timer 26 is started.
When the broadcast frame completes one round, the flip-flop 21 is set by the broadcast frame detection pulse signal 31 output from the reception control section. Further, the flip-flop 22 is set by a pulse signal 32 output when the source address matches the local station address. An FCSOK signal 33 indicating that the flip-flops 21 and 22 and the frame check sequence FCS are correct is input to the AND gate 23. Its output is input to the K input of flip-flop 25 and the set input of flip-flop 24, and when flip-flop 25 is reset, watchdog timer 26 is stopped. flipflop 2
The cycle completion signal 36, which is the output of step 4, serves as an interrupt signal to the microprogram as a transmission completion signal, similar to the response reception in the individual signal. Further, when the flip-flop 24 is not set, the timeout signal 35 of the supervisory timer 26 becomes an interrupt signal to the microprogram, which is treated as a no response or a busy response in individual communication, and serves as a retransmission trigger for the transmission operation. The timer 27 is activated by the transmission activation signal 34 in the same manner as described above, and after a predetermined time, it always outputs the transmission trigger signal 37, generates a timer interrupt, and provides a data frame transmission trigger to the microprogram.

FIG. 4 is a diagram showing the operation of the broadcast communication device of the present invention when retransmitting broadcast communication. Generally, in order to increase the success rate of communication between host processors, before transmitting broadcast data, a broadcast command frame is transmitted to the receiving station to indicate that data will be transmitted subsequently. This provides preparation time for securing a reception buffer and generating a notification interrupt to the host processor.

When playing a broadcast frame, the timeout of the round monitoring timer is used as a trigger, so it is possible that there are stations that have already received it for the first time and stations that have not received it yet. . The purpose of retransmission is to retransmit to the latter, but since it is a broadcast communication, it is also retransmitted to the former. Therefore, it is important to ignore the former station as a redundant transmission, and this point will be explained below.

In FIG. 1, station A is a transmitting station, stations B,
Let C and D be receiving stations. In FIG. 4, station A starts transmitting a broadcast command frame and at the same time activates a round monitoring timer T ₁ (timer time Ta) and a timer T that waits for data transmission in order to wait for the completion of individual transmission and to give preparation time on the receiving station side. ₂ (timer time Tb)
and start. Station A, which has detected the timeout of the cycle monitoring timer _T1 , retransmits the data a predetermined number of times within the timer time Tb.

On the other hand, in the receiving station, the station that received the first broadcast command frame suppresses the activation of new individual transmission and starts the broadcast reception data frame wait monitoring timer _T4 .
(Timer time Td) is started. Once the monitoring timer _T4 is started, the mode is set to ignore broadcast command frames (rejects them even if they are received), and only broadcast data frames that are distinguished from broadcast command frames are received. If the broadcast data frame is not received within the timer time Td, the monitoring timer _T4 is reset, the broadcast reception operation ends, and a new broadcast command frame can be accepted.

Monitoring timer _T3 (timer time Tc) existing in station A
is a transmission interval management timer for transferring the next broadcast data frame after waiting for the receiving buffer on the receiving station side to become empty, and can be realized by changing the value of timer _T2 . Each timer time must satisfy the relationship Td>Tb>Tc>Ta·n, where n indicates the number of retransmissions.

FIG. 5 is a flowchart of the transmitting station of the broadcast communication device of the present invention. Figure 5 describes the case of command transmission. After detecting the timeout of timer time Tb, timer T ₁ and timer
This can also be applied to data frames by replacing the box indicating T ₂ start with timer T ₁ and T ₃ start, and replacing the box indicating timer T ₂ timeout with timer T ₃ .

FIG. 6 is a flowchart of the receiving station of the broadcast communication device of the present invention. Reception processing is started by a busy interrupt indicating that valid data exists in the reception buffer, and processing is performed by the interrupt routine up to the start of monitoring of the monitoring timer _T4 , and the cycle of monitoring timer T4 is started.
Enables removal of redundant frames during _T1 operation. As a method for determining whether a frame is a redundant transmission frame, in the case of a command frame, a method of comparing it with the first command frame is used.
Further, in the case of a data frame, the frame sequence numbers present in the transfer information I field indicating the distinction between a command frame and a data frame are compared, and if they match, it is regarded as a redundant frame.

〔Effect of the invention〕

As explained above, the present invention has the excellent effect of enabling retransmission even in broadcast communication in a loop network. Therefore, there is an advantage that communication reliability can be improved against intermittent failures.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a broadcast communication device according to an embodiment of the present invention. FIG. 2 is a block diagram of the broadcast frame control monitoring timer of the broadcast communication apparatus of the present invention. FIG. 3 shows a packet frame of the broadcast communication device of the present invention. FIG. 4 is a diagram showing the operation of the broadcast communication device of the present invention when retransmitting broadcast communication. FIG. 5 is a flowchart of the transmitting station of the broadcast communication device of the present invention. FIG. 6 is a flowchart of the receiving station of the broadcast communication device of the present invention. 21, 22, 24, 25...Flip-flop, 23...And gate, 26...One cycle monitoring timer, 27...Waiting timer, 31...Broadcast frame detection pulse signal, 32...Pulse signal, 33
...FCSOK signal, 34 ...Transmission start signal, 35
...Timeout signal, 36...One round completion signal,
37... Transmission trigger signal, A, B, C, D...
Station, T ₁ , T ₂ , T ₃ , T ₄ ...Timer, W, X, Y,
Z...Host processor.

Claims (1)

[Claims] 1. A plurality of stations connected via a loop network and sequentially transmitting and receiving broadcast frames including command frames and data frames; and a station connected to each of the plurality of stations to control broadcast communication. In a broadcast communication method that transmits a broadcast command frame indicating that a broadcast data frame will be transferred before transmitting a broadcast data frame, each host processor has a , a first timer means that is activated when a broadcast frame is transmitted and monitors one cycle of the broadcast frame; a second timer means that is activated when a broadcast frame is transmitted and waits for the transmission of the next broadcast frame; retransmission means that is activated when the first timer means times out and retransmits the broadcast frame within the timer time of the second timer means; A third timer means that waits for a broadcast frame; and a third timer means that is activated when the broadcast frame is received, and while the third timer means is in operation, the second and subsequent broadcast frames received by retransmission are ignored as redundant transmissions. A broadcast communication system characterized by comprising a means for ignoring.