JPH084268B2 - Retransmission method in broadcast communication - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a local area network, and more particularly to a retransmission method for broadcast communication in a loop network.

[Conventional technology]

As a communication method in a local area network, the method of transmitting the same data frame from one station to all other stations simultaneously is called broadcast communication. Generally, in a broadcast communication, since it is difficult to use a response confirmation method, there is a problem in the retransmission timing at the transmitting station and the recognition of the retransmission frame at the receiving station side, and the retransmission has not been performed.

[Problems to be solved by the invention]

Since the above-mentioned conventional broadcast communication does not perform response confirmation and resend, if there is an intermittent failure on the transmission line or the receiving station side or if the load on the receiving station side due to individual communication is large, the broadcast communication frame is There is a drawback that the communication is not reliable because it may not be received.

[Means for solving problems]

According to the present invention, in the case where a command and a data frame are transmitted and received in sequence in a broadcast communication of a loop network, a first timer means for round trip monitoring and a data frame The second time means for waiting the transmission is activated, and the time-out of the first timer means
When the retransmission is performed within the set time of the second timer, the means for setting the retransmission frame flag in the frame is caused to function,
On the other hand, in the receiving operation, when the command frame is received, the third timer means for waiting the data frame is activated, and the second and subsequent command frames received by the retransmission during the operation of the third timer are redundant. The means for ignoring the transmission as a function is also operated, and similarly, the means for activating the third timer means when the data frame is received and ignoring the second and subsequent data frames received by the retransmission as the redundant transmission is also functioned. By doing so, it is possible to obtain a retransmission method in broadcast communication characterized by preventing double reception of a command frame and a data frame.

〔Example〕

FIG. 2 shows packet frames transmitted and received between the stations of the loop network used in the embodiment of the present invention.

The packet frame consists of a time fill TF that fills in between frames, a delimiter F that indicates the start of the frame, a destination address DA,
Source address SA, loop command LC indicating frame type (token, response, information), control information CI indicating command / data distinction, information I indicating original transfer information, frame check sequence FCS, indicating end of frame It consists of delimiter F and each field of time film TF that fills in between frames.

By the way, when the DA field is "FF" indicating all "1", it is called a broadcast frame, and each receiving station on the loop network is obliged to receive and relay.

As one of the features of the present invention, as shown in the enlarged view of the LC field in FIG. 2, a retransmission frame flag indicating a retransmission frame, that is, a retransmission designation bit is added in this field. The retransmission designated bit does not have to be in LC, but may be in CI or I field. That is, the retransmission designation bit is used as "0" in the first transmission and "1" in the second and subsequent transmissions, and is provided in the receiving station to easily determine the redundant frame of the broadcast frame. As a result, once the redundant transmission frame removal mode is set by the first reception, it is possible to determine the redundant transmission frame only by checking the retransmission designation bit.

FIG. 3 shows a loop network for mutual communication using the packet frames shown in FIG. The host processors W, X, Y, and Z perform data transmission / reception operations with each other via stations A, B, C, and D connected to the loop-shaped transmission path. As a characteristic of the loop transmission line, when a broadcast transmission frame from the host processor W is transmitted from the A station, it is transferred in the fixed directions of the B, C, and D stations. Then, each station executes a reception operation and a relay operation, and the broadcast data is transferred to each host processor X, Y, Z.
The broadcast transmission frame relayed at station D goes back to station A again. At this point, station A deletes the broadcast transmission frame by stopping the relay operation at the same time as detecting the complete broadcast transmission frame.

In station A, a round trip check can be performed by starting the round trip timer at the start of transmission and stopping the round trip timer when a round frame is detected. on the other hand,
If a time-out occurs without detecting a single frame, it is considered that an intermittent failure has occurred on the transmission path and is used as a trigger for retransmission.

FIG. 4 shows an operation diagram when the broadcast communication is retransmitted.
Generally, in order to increase the success rate of communication between host processors, a broadcast write command (hereinafter referred to as W command) indicating that data will be continuously transferred before transmitting broadcast data. Is transferred to secure the receiving buffer for the receiving station and give the host processor a preparation time for generating a notification interrupt.

When the broadcast frame is retransmitted, the timeout of the round-robin monitoring timer is used as a trigger, so it is possible that there are stations that have already received the first station and stations that have not received the station. . The purpose of resending is to resend to a station that has not received, but due to the broadcast communication, it is also resent to the receiving station. Therefore, it is important for a station that has already received the packet to ignore the retransmission frame as a redundant transmission, and this point will be described.

Here, station A is the transmitting station and stations B, C, and D are the receiving stations.

In Figure 4, A station, and at the same time start sending broadcast W command, wait for data transmission to provide round monitoring timer T _a and preparation time of individual transmission termination waiting and receiving station of the time setting t _a Start the waiting timer T _b for the set time t _b . When the station A detects the time-out of the loop monitoring timer T _a , it also retransmits the broadcast frame a predetermined number of times within the set time t _b of the waiting timer T _b .

On the other hand, the station that receives the first W command at each receiving station suppresses the activation of new individual transmission and sets the set time t _d.
Starts the broadcast reception data waiting monitoring timer T _d . Once
When this reception monitoring timer is started, the broadcast W command is ignored (that is, it is not accepted even if it is received), and only broadcast data distinguished from the broadcast W command is received. Not receive the broadcast data within the set time t _d, and resets the timeout of the reception monitoring timer T _d, the broadcast data receiving operation is terminated, to allow acceptance of a new broadcast command.

The monitoring timer of the set time t _c existing in the station A is a timer that manages the transmission interval for transferring the next broadcast data after waiting for the receiving buffer on the receiving side to become empty. That is,
The timer T _{c is} also a timer means for waiting the transmission of the data frame, like the waiting timer T _b . Incidentally, the timer because the queuing timer T _b do not overlap in time, can be combined by changing the set time of the queuing timer alternately.

The set time of each timer needs to satisfy the relationship of t _d > t _b > t _c > t _a · n, where n represents the number of retransmissions.

FIG. 5 shows an operation flowchart in the transmitting station. Although this figure describes the case of W command transmission, the step 1 indicating the start of the monitoring timer T _a and the waiting timer T _b is shown as the timer T _a and the timer T _c after the waiting timer T _b times out. It can also be applied to the case of data transmission if it can be read that it starts.

Retransmission is realized by setting the LC field shown in FIG. 2, assembling the frame in the transmission buffer, and starting transmission by step 4 which indicates the retransmission designation bit setting.

FIG. 6 shows an operation flowchart in the receiving station.
The reception process is started by the Jibby interrupt that indicates that valid data exists in the reception buffer, and the reception monitoring timer
Until the start of T _d monitoring, it is processed by the interrupt routine, and the removal operation can be performed for the redundant frame during the reception monitoring timer T _d operation. Since the retransmission refusal flag is set in the first reception, the second and subsequent frame receptions can be judged as redundant transmission only by checking the retransmission specification bit, and the comparison operation of the entire frame is not required.

FIG. 1 shows a control circuit of a broadcast frame control timer in each station. The flip-flop (hereinafter abbreviated as F / F) 25 is a transmission start signal TXRQ input to its J input terminal.
It is set by 34 and the open loop monitoring timer T _a 26 is started. When the broadcast frame has completed one cycle, the F / F21 is set by the broadcast frame detection pulse signal 31 output from the reception control unit. Also, the F / F 22 is set by the pulse signal 32 output when the source address matches the own station address. F / F21
Output, F / F22 output and frame check sequence FC
FCSOK signal 33 indicating that S was correct is AND gate 23
Is input to. The output of the AND gate 23 is input to the K input terminal of the F / F 25 and the set input terminal of the F / F 24. When the F / F 25 is reset, the loop monitoring timer T _a 26 is stopped. F / F24
The output 36 of 1 indicates completion of one round, and becomes an interrupt signal to the microprogram as a completion signal of transmission similarly to response reception in individual communication. When the F / F24 is not set, the timeout (TO) signal 35 of the round-trip monitoring timer T _a 26 becomes an interrupt signal to the microprogram, and it is regarded as no response or busy response in individual communication. It triggers the resending of the sending operation. The timer 27 is the timer as described above.
It is also used as T _b and timer T _c , and is activated by the transmission activation signal 34 in the same manner as the timer T _a and always generates a timer interrupt after a fixed time and gives a transmission trigger of a data frame to the microprogram.

On the other hand, in the receiving operation, the reception monitoring timer T _d 41
When a global W command or a data frame other than the last frame is received, it is activated by a signal 40 (at the time of step 2 in FIG. 6) from the micro instruction control to wait for the next data When the is received, the counting operation is stopped. When the micro-instruction control unit detects the time-out signal 42, the reception operation is abnormally terminated and a series of operations are performed.

〔The invention's effect〕

As described above, according to the present invention, by using the retransmission method even in the broadcast communication of the loop network,
It has the effect of improving the reliability of communication against intermittent failures.

[Brief description of drawings]

FIG. 1 is a block diagram showing an essential part of one embodiment of the present invention,
FIG. 2 is a diagram showing a frame format used in the loop network, FIG. 3 is a block diagram showing the loop network, and FIG. 4 is an operation explanatory diagram showing each timer monitoring period and retransmission operation in FIG. FIG. 5 shows a flow chart including the retransmission operation of the broadcast transmission, and FIG. 6 shows a flow chart including the redundant transmission frame removal operation of the broadcast reception. In the figure, 21,22,24,25 …… Flip-flop, 23 …… And gate, 26,27 …… Timer.

Continuation of the front page (56) Reference JP-A-59-158160 (JP, A) JP-A-57-123754 (JP, A) JP-A-56-169448 (JP, A) JP-B 5-68902 (JP , B2)

Claims (1)

[Claims] 1. In a broadcast communication of a loop network, when command and data frames are transmitted and received in sequence, first timer means for round trip monitoring at the time of starting transmission of command frames and data frames, and transmission of data frames. Means for setting a retransmission frame flag in the frame when the second timer means for waiting is activated and the retransmission is performed within the set time of the second timer means due to the timeout of the first timer means. On the other hand, in the receiving operation, when the command frame is received, the second and subsequent command frames received by the retransmission during the operation of the third time means for waiting the data frame are ignored as a redundant transmission means. Function,
Similarly, when the data frame is received, the third timer means is activated, and the means for ignoring the second and subsequent data frames received by the retransmission as redundant transmission is made to function, thereby making the command frame and the data frame. Retransmission method in broadcast communication, which is characterized by preventing double reception of.