JPS59172859A - Retransmission system - Google Patents

Abstract

PURPOSE:To transmit with priority a frame during processing of backoff by limiting the start of transmission of frame of a new station during the backoff processing time in a bus type local area network. CONSTITUTION:When stations STN1 and STN2 transmit a data of a transmission frame to a coaxial cable 4 at the same time, collision is detected at each transceiver 2 and it is informed to the STN1 and STN2 via a collision detection signal line 53. The state of collision is detected by each transceiver 2 and it is informed on the signal line 53 to STN3-STNn not performing frame transmission. The STN3-STNn become in the state of transmission stop after this point of time, and after the STN1 and the STN2 stop the frame transmission after a prescribed time, they transmit the retransmission frame by means of the backup processing with priority. When a carrier by the retransmission frame is detected twice by a carrier detecting circuit 13, the STN3-STNn discriminate that the frame transmission from the STN1 and STN2 is finished, and release the transmission stop state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a transmission frame retransmission system suitable for use in a bus-type local area network.

[Technical background of the invention and its problems]

In recent years, many local area networks have been announced that interconnect computer equipment distributed within a building. Among them, ETHER proposed by the American company Xerox
NET is a well-known network with a path structure.

This ET) 1ERNET system is C8MA/CD (carrier sense multiple access/collision).
Detect) is used. That is, when there are many carriers on the bus, any station can send data onto the bus. Therefore, when two or more stations transmit data at the same time, a collision occurs.When a station detects a collision, it immediately stops transmitting data, and waits for a certain period of time before retransmitting data. The time until retransmission can be independently selected by each station using random numbers. This is usually called backoff processing. According to this method, if a new station starts transmitting during this backoff processing time, another collision may occur. This frequent occurrence of collisions on the bus degrades the throughput and performance of the system, and it is necessary to control them to prevent them from occurring as much as possible.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a retransmission method that prioritizes transmission of frames undergoing backoff processing by restricting the start of transmission from new stations during backoff processing time. shall be.

[Summary of the invention]

The present invention provides a bus-type local area network based on the C8MA/CD system, during bank-off processing time.
This restricts the start of frame transmission from new stations, and sends frames undergoing backoff processing with priority.

For example, assume that stations 1 to n are connected to a bus, and that stations 1 and 2 simultaneously send frames and a collision occurs. At this time, the other stations 3 to n connected to the bus (which are not transmitting frames at the time of vi accident detection) also detect this, and from this point on, frame transmission from their own station is stopped until instructions are given. do.

Stations 1 and 2 that have caused a collision stop frame transmission after a sufficient time has elapsed for other stations 3 to n to record the @ arrow state, and preferentially send out retransmitted frames through backoff processing. After the other stations 3 to n detect the sending of the retransmission frame (twice) by the station 1.2, they release the transmission stop state of their own stations.

As a result, during the backoff processing time, the start of frame transmission by a third party station is restricted, and the frame being processed for backoff processing can be transmitted with priority.

Therefore, response time is improved and system performance is further positively affected.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the drawings.
FIG. 2 is a diagram showing a connection configuration of a bus-type local area network.

In the figure, each station 7 (STN1~n
) are connected to each other via the transceiver 2 and the coaxial cable 4. A terminator 3 is provided to match the terminal impedance of the coaxial cable 4. A transceiver cable 5 connects the transceiver 2 and the station l.

FIG. 2 is a block diagram showing a schematic internal configuration of the transceiver shown in FIG. 1.

In the figure, 21 is a collision detection circuit including a circuit for signal transmission/reception 4m. 22 is a signal level conversion circuit of the interface. 51 is a transmission signal line, 52 is a receiver signal line, and 53 is a collision detection signal line.

FIG. 3 is a block diagram showing a partial schematic internal configuration of the station 1 shown in FIG.

In the figure, 11 is a data transmitting circuit, 12 is a data receiving circuit, 13 is a carrier detection circuit, and 14 is a control circuit composed of a microprocessor.

FIG. 4 is a diagram chronologically showing an example of a retransmission sequence according to the conventional method, and FIG. 5 is a diagram chronologically showing a retransmission sequence according to the present invention.

Hereinafter, the operation of the present invention will be explained in detail while comparing it with the conventional system. First, a conventional retransmission method after a collision occurs will be described. Now, stations 5TNI and 5 in Figure 1
It is assumed that TN2 and TN2 issued transmission requests at almost the same time.
8TN.

and s'rNt respectively detect the absence of a signal carrier on the coaxial cable 4 by the no signal on the receiving signal line 52, and start transmitting frames.
t start transmitting at the same time, and therefore a collision occurs on the coaxial cable 4. 5TNI and 5TN2 are
This collision state is detected by the collision detection signal line 5 from the transceiver 2.
3, and after maintaining the collision state for a certain period of time, transmission is stopped. S T N s and S T N x each retransmit their respective frames after waiting times determined by independent random numbers. As mentioned above, these retransmission sequences are called backoff processing. However, as shown in the time chart in Figure 4, 5TNs and S T N
When t causes a collision and is retransmitted, a new third S
If T N n starts transmitting, a collision may occur again. As mentioned above, if collisions occur frequently on the line, the system will be adversely affected.

In view of these points, the present invention limits the frame transmission of the third station during backoff processing, so that the first colliding frame is transmitted preferentially. The method of the present invention will be described in detail using FIGS. 1, 2, 3, and 5.

Now, consider a case where the 5TNI and STN issue transmission requests at the same time. When the control circuit 14 of each station confirms that there is no signal from the carrier detection circuit 12, it supplies the data of the transmission frame to the data transmission circuit 11. The data transmission circuit 11 converts this data into a serial data transmission code, and transmits it via the transmission signal line 5 and the transceiver 2.
It is sent to the coaxial cable 4. Thus, signals are sent out simultaneously from transceiver 2 connected to 5TN1 and transceiver 2 connected to 5TNz, and a collision occurs. STN.

and s'rNt are notified of the collision detected by each transceiver 2 by the collision detection signal line 53Vr. At this time, S', T, which is not transmitting a frame
The transceiver 2 of Ns...5TNn also detects this collision condition and notifies each STN,...5TNn via the collision detection signal line 53. Upon receiving this, these stations stop transmitting from this point onwards. On the other hand, 5TN1 and STN each stop transmitting frames after a predetermined time after detecting the collision.

The predetermined period of time refers to a period of time sufficient for non-transmitting stations to recognize the collision state. Here, STN.

Since stations other than s'rNt and s'rNt are in a transmission-stopped state, retransmission frames by the /XI cut-off processing of STN and 5TNt are sent out preferentially. Stations other than 5TNI and STN, when the carrier detection circuit detects the carrier due to the retransmitted frame twice, switch off the 5TN1 and STN by the size cut-off process.
It is determined that retransmission of the frame from 1 is completed, and the transmission stop state is canceled. Moreover, when this transmission stop state is canceled, the frame may not be retransmitted due to a failure or the like. In such a state, the transmission stop state is canceled by the elapsed timer.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent a new frame from colliding during the bank-off processing time, which means that the frame of the station that collided first is processed preferentially. Therefore, it contributes to improving response time and system throughput.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the connection configuration of a bus type local area network, FIG. 2 is a block diagram showing a schematic internal configuration of the transceiver shown in FIG. 1, and FIG. A block diagram showing a partial internal configuration,
FIG. 4 is a diagram chronologically showing an example of a retransmission sequence according to the conventional method, and FIG. 5 is a diagram chronologically showing a retransmission sequence according to the present invention. l...Station (STN, ~5TNn), 2.
... Transceiver, 3... Terminator, 4... Coaxial cable (bus), 5... Transceiver cable,
11... Data transmitting circuit, 12... Data receiving circuit, 13... Carrier detection circuit, 14... Control circuit,
21... Collision detection circuit, 22... Level conversion circuit.

Claims (3)

[Claims] (1) Two or more stations are commonly connected on the bus,
In a local area network in which any station sends data to the bus when there is no carrier on the bus, each station monitors the collision status of sending frames on the bus, and backs up after a collision is detected. Retransmission method 0 characterized in that when retransmitting a frame due to off processing, a station that is not transmitting a frame sends out the conflicting frame preferentially by restricting the start of frame transmission from its own station. (2) After detecting the collision, each station that sent the collision frame stops transmitting the frame after a predetermined period of time (a time long enough for stations that were not transmitting frames at this time to recognize the collision state). The retransmission method according to claim 1, wherein backoff processing is started after confirming the station's transmission stop state. (3) When a frame collision is detected, each station that did not send a frame releases its own transmission stop state after detecting that the frame retransmission due to the back-off process of the station that sent the frame has been completed. A retransmission method according to claim (1), characterized in that the retransmission method performs the following.