JPH0787467B2 - Storage-type star communication network - Google Patents

Description

TECHNICAL FIELD The present invention relates to a storage-type star communication network, and in particular, eliminates data collision on the line and enables efficient use of the line. It relates to a storage-type star communication network.

(Prior Art) A conventional star communication network will be described with reference to FIG.

As shown in the figure, the conventional star communication network has a central station 1
In addition, a plurality of station terminal devices A to N are connected via transmission lines 2a to 2n and reception lines 3a to 3n.

Now, when a data packet is transmitted from the terminal device A of the station A, the data packet passes through the transmission line 2a of the station A and the central station 1
Sent to. When the central station 1 receives the data packet from the terminal device A of the station A, it sends it to all the terminal devices, and the reception lines of the stations A to N.
Send via 3a-3n. Each of the terminal devices A to N determines whether or not the transmitted data packet is addressed to itself, and if it is addressed to itself, receives the data packet.

Each terminal device constantly monitors the signals coming in from the reception lines 3a to 3n, and if any data packet is transmitted to the reception line, it cannot transmit from its own station. The existing terminal device starts transmission after waiting for the end of reception of the data packet. At this time, if there are transmission requests from two or more stations, data packet transmission is started at the same time, resulting in data packet collision. This collision is detected by the central station 1. When the centralized station 1 detects a collision, it notifies all the terminal devices A to N of this.

When the centralized station 1 is informed that a collision has occurred on the network or line, the terminal device transmitting the data causing the collision stops the transmission. Then, a process for retransmitting such as a backoff algorithm is performed.

This situation will be described with reference to the time chart of FIG. First,
If there is a transmission request from the station A terminal device, the data packet (station A packet) sent from the station A terminal device is A
It is sent to the central station 1 via the station transmission line 2a, and then each reception line
Sent to 3a-3n. When a request for transmission is made from the terminal devices of the stations B and C while the packet of the station A is transmitted, these terminal devices wait for the end of the transmission of the packet of the station A and start sending them all at once. Then, data collision occurs on the network, and the central office 1 sends a collision signal to each of the reception lines 3a to 3n. Therefore, the B and C station terminal devices stop transmission. When the processing for re-sending such as the back-off algorithm is completed, the D station terminal device which has requested the transmission after the collision acquires the transmission right and sends the data packet (D station packet).

(Problems to be Solved by the Invention) The above-described conventional technique has the following problems.

(1) When sending a data packet, each terminal device must judge whether or not another station is sending the data packet, and in the event of a collision, it must stop sending the data packet and perform re-sending processing using a backoff algorithm or the like. Therefore, the hardware and software configuration of each terminal device becomes complicated.

(2) Since a collision occurs and each terminal device cannot send out a data packet to the network while the collision signal is output from the centralized station 1, the probability of collision if the number of terminal devices accessing the network increases within a certain time. Grows larger. Therefore, the collision signal is output from the central station 1 for a long time, and only a transmission capacity much lower than the actual physical transmission capacity is guaranteed.

(3) Since the minimum packet length must be longer than the maximum system round trip time in order for all terminal devices to perform collision detection, the maximum system length is limited by the minimum packet length. Therefore, the system construction lacks flexibility.

The present invention has been made to solve the above problems.

(Means and Actions for Solving Problems) In order to solve the above problems, the present invention centrally relays a plurality of terminal devices and data packets transmitted from those terminal devices, In a star communication network having a centralized station to be distributed to each terminal device and a bidirectional communication channel between each terminal device and the centralized station, at least one data packet each received at each terminal interface of the centralized station is received. A memory, a control circuit for monitoring the status of the receiving memory and sequentially sending a read signal to the receiving memory containing data, and means for transmitting the data read from the receiving memory to all the receiving lines are provided. , Temporarily store the data packet output from each terminal device in the reception memory,
By sequentially reading data from the reception memory and sending it to each terminal device, collision at the time of transmission can be avoided, and the transmission amount can be effectively used up to near the maximum transmission capacity of the communication network. Another feature is that the maximum system length is no longer limited.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.

As shown in the drawing, the A, B, ..., N station terminal devices are connected to the central station 5 via transmission lines 6a, 6b, ..., 6n and reception lines 7a, 7b ,. ing. The central station 5 has reception memories 5a, 5b, ..., 5n corresponding to the A, B, ..., N station terminal devices provided in each terminal interface and the storage states thereof, and holds data. It has a control circuit 5p for sequentially outputting a read signal to the reception memory, and a transmitter 5r for distributing / transmitting the data read from the reception memory to the respective reception lines 7a, 7b, ..., 7n. Each of the reception memories 5a, 5b, ... 5n has a capacity equal to or larger than the maximum length of one data packet. The transmission line and the reception line may be physically independent cables, or a single cable may be used for both transmission and reception channels.

Next, the operation of this embodiment will be described in detail. When a transmission request is issued to a terminal device of A, B, ..., N station, the terminal device that has made the transmission request sends a data packet to the reception memory corresponding to the station through the transmission line of the station. The data packet is thereby stored in the receiving memory.

The receiving memory has the function of sending out an empty signal when the data is empty and an empty signal when the data is stored. The memory sends an off empty signal to the control circuit 5p through the corresponding signal line in the empty signal lines La, Lb, ..., Ln.

On the other hand, the reception memory to which the data packet has not been sent from the terminal device sends an on-empty signal to the control circuit 5p through the corresponding signal line among the signal lines La, Lb, ... Ln.

The control circuit 5p constantly monitors the status of each reception memory by polling the empty signals La, Lb, ..., Ln, and reads in a predetermined order in the reception memory in which the empty signal is off ( read) Send a signal. This read signal is sent to the reception memory through the control signal lines Ra, Rb, ..., Rn.

The receiving memory to which the read signal is sent reads the data on the data bus B at the same speed as the network, and when all the data is read, it sends an empty signal to the control circuit 5p. Then, the read signal is sent to the next reception memory having the empty signal which is off to the control circuit 5p.

The function of this control circuit 5p is shown in the flowchart of FIG. The control circuit 5p goes to the empty signal of the receiving memory of a certain station (step S1) and judges whether this signal is on or off (step S2). When the empty signal is on, since the data packet is not held in the receiving memory, the process returns to step S1 to see the empty signal of the receiving memory of the next station. When it is determined in step S2 that the empty signal is off, a read signal is sent to the reception memory to read data at the same speed as the network (step S3). During this data read period, the control circuit 5p always makes the determination in step S2,
It is always checked whether the reading of data from the receiving memory is completed. Then, when step S2 becomes YES, it is judged that the reading of the data from the receiving memory is completed, and the operation of going to the empty signal of the receiving memory of the next station is performed.

The above operation will be described more specifically. In FIG.
Assuming now that three data packets of the A, B and M station reception memories are stored and not stored in the other reception memories, the control circuit 5p receives the empty signals from the empty signal line to receive the received memories. Station A reception memory that stores the data packet
A read signal is sent to 5a via the control signal line Ra. Then, the data packet is read from the reception memory 5a of station A onto the data bus B from the beginning and sent to the transmitter 5r at the same speed as the network speed. Transmitter 5r
The data packet is distributed / transmitted to the reception line of each station. Each terminal device determines whether or not the transmitted data packet is addressed to its own station, and if it is addressed to its own station, receives it.

When all the data in the A station reception memory 5a has been output through the data bus B as described above, the control circuit 5p sends a read signal to the B station reception memory 5b, which is the next reception memory containing the data. Send out. On the other hand, the A-station reception memory 5a sends an ON empty signal to the control circuit 5p.

After confirming that the transmission of the data packet of the station A is completed, the station A accepts a new transmission request from the upper layer. On the other hand, since the B and M station reception memories are still holding the data packets and are not in the state of sending the data packets, the B and M station terminal devices receive a new transmission request from the upper layer. Data packets cannot be sent to the receiving memory. In addition, terminal devices other than B and M station terminal devices,
Of course, the transmission request from the upper layer is accepted.

From the station B reception memory 5b, data is read onto the data bus B from the beginning of the data packet in the same manner as described above.
When this reading is completed, the control circuit 5p sends a read signal to the M station reception memory. The station B reception memory 5b outputs an empty signal which is on.

Next, data is read from the M station reception memory 5m in the same manner as above.

When the data read from the M station reception memory 5m is completed, the control circuit 5p checks by polling whether or not the OFF empty signal is input from the reception memory. Then, if there is a receiving memory whose empty signal is off, a read signal is sent to this receiving memory to read the data.

Since the conditions for the terminal devices of the A to M stations to accept the transmission request from the upper layer are as described above, when there is a transmission request from the upper layer in the empty reception memory, a data packet is sent from the corresponding terminal device at any time. It is natural to be sent.

Since this embodiment operates as described above, for example, the third
As shown in the time chart of the figure, station A, station B,
Even if the transmission requests from station C and station D occur within a short time as shown in the figure, if the reception memories 5a, 5b, 5c and 5d corresponding to these stations are empty, each terminal device Data packets can be sent out via transmission lines 6a, 6b, 6c and 6d. In addition, the data packet output from each of these terminal devices is temporarily stored in the reception memory,
As described above, the control circuit 5p sends the signal to the receiving lines 7a to 7n of each station through the transmitter 5r without causing any collision.

(Effects of the Invention) According to the present invention, since collision of data packets does not occur on the network, the following various effects are achieved.

(1) Since the invalid data generated by the collision does not flow on the line, the line can be efficiently used up to near the physical capacity.

(2) The central station does not need to detect a collision or send a collision signal. Further, each terminal device does not need a process of stopping the transmission of the data packet at the time of collision, or a process of retransmitting a backoff algorithm. This simplifies both hardware and software.

(3) Since it is no longer necessary to set the maximum system length required for collision detection, the maximum system length depends on the capabilities of the driver and the receiver at both ends of the transmission / reception line. Further, if a through repeater or the like is used, the system length can be extended to a distance far beyond the capabilities of the driver and receiver. Therefore, a large system can be created. It is obvious that a gateway can be used to communicate with a terminal device of another system.

(4) According to the present invention, data can be read out directly from the receiving memory containing data at the same speed as the transmission speed of the network and transmitted to all the receiving lines. For this reason,
It is no longer necessary to transfer the data stored in the reception memory to a buffer and send it to all reception lines, and control and overflow of how to transfer received data from a plurality of stations to the buffer. There is no need to perform complicated control of transferring the data to the buffer. Therefore, the configuration of the central station can be simplified and the communication speed of the entire network can be made constant.

[Brief description of drawings]

FIG. 1 is a system block diagram of an embodiment of the present invention, and FIG.
FIG. 4 is a flow chart showing the function of the control circuit of FIG. 1, FIG. 3 is a time chart for explaining the operation of this embodiment, FIG. 4 is a conventional system block diagram, and FIG.
The time chart for demonstrating the operation | movement of a figure is shown. A, B, ..., N ... Station terminal device, 5 ... Central station, 5a-5n ... Reception memory, 5p ... Control circuit, 5r ... Transmitter, 6a
〜6n …… Transmission line, 7a ～ 7n …… Reception line

Claims (1)

[Claims] 1. A plurality of terminal devices, a central station that centrally relays data packets transmitted from these terminal devices and distributes to each terminal device, and bidirectionality between each terminal device and the central station. In a storage-type star communication network having a communication channel, each terminal device receives a data packet requested for transmission at the central station at any time except when data is held in a corresponding reception memory. The centralized station has means for transmitting to a memory, and the centralized station has an empty capacity provided for each terminal interface of the centralized station, the empty capacity indicating at least one data packet and indicating whether or not data is held. A receiving memory that outputs a signal to the control circuit, and the status of the receiving memory is monitored by polling, and a read signal is sequentially sent to the receiving memory containing data. A control circuit, means for reading data from the receiving memory to which the read signal is sent at the same speed as the transmission speed of the network, and means for transmitting the data read from the receiving memory to all the receiving lines. A storage-type star communication network characterized by the above.