JPS61187445A - Packet transmission control system - Google Patents

Abstract

PURPOSE:To transmit a retransmission packet in a short time with simple processing by using a reception busy field to inform the disabled reception of a sender communication controller when no packet is received because no idle reception buffer memory exists, allowing the sender communication controller receiving the notice to reset the reception busy field of the packet and transmit it as a transmission packet. CONSTITUTION:Even when a branching/insertion control section 7 identifies that a reception packet (a) is effective and addresses to the own device, if an unreceivable signal (c) is added, the section 7 sends the packet not received while setting the reception busy field BY as busy. The sender communication controller discriminates that the packet is a packet not received by a destination communication controller, resets the reception busy field BY and sends the packet to a transmission line from an output terminal 11 via selector 4 as it is.

Description

[Detailed Description of the Invention] [Summary] In a transmission system in which communication control devices are connected in a loop to packetize communication data between terminal devices and send it out to a transmission path, a receiving side communication control handles transmitted packets. If the packet cannot be received, the packet is circulated using a loop-shaped transmission path, thereby simplifying packet retransmission control.

[Industrial application field]

The present invention relates to a packet retransmission control method for retransmitting packets not received within a loop transmission network with simple control.

A loop transmission network in which communication control devices connected to a plurality of terminal devices are connected in a loop through a transmission path such as a coaxial cable has a configuration as shown in FIG. 4, for example. In the figure, IA, IB, IC, and ID are communication control devices, 2 is a transmission path, and 3 is a terminal device. Terminal device 3
The communication data between them is sent to the transmission path 2 as a packet with a header including a destination address, a source address, etc. Each communication control device IA to ID identifies whether or not the packet is addressed to its own device based on the destination address, and if it is addressed to its own device, it takes in the packet, and if it is addressed to another device, it
A transmission method is adopted in which the data is relayed as is.

[Conventional technology]

In the loop transmission network shown in FIG. 4, communication control devices IA to I
D is equipped with a transmission buffer memory and a reception buffer memory, and controls the transfer of packets addressed to the device itself to the terminal device 3 after once storing them in the reception buffer memory, and also controls communication data from the terminal device 3. After storing the packets in the transmission buffer memory, the packets are controlled to be sent to the transmission path 2 at a timing according to the transmission method.

Therefore, a packet sent from the source communication control device to the transmission path 2 may not be received because there is no free space in the reception buffer memory of the communication control device specified by the destination address. In this case, the data stored in the communication control device of the source is sent as a retransmission packet to the transmission path.

[Problem that the invention seeks to solve]

The source communication control device needs to save a copy of the transmitted packet in case retransmission processing is necessary, and a buffer memory must be provided for this purpose. Furthermore, since retransmission processing is controlled at a logical level, it has the disadvantage that the time required for retransmission is long.

The present invention improves the above-mentioned conventional drawbacks and enables retransmission processing in a short time by simple control.

[Means for solving problems]

The packet retransmission control method of the present invention will be explained with reference to the principle block diagram shown in FIG. When the drop-and-insert control unit 7 determines that the packet PT cannot be received, it sets the packet PT reception and G-field BY and notifies the source communication control device 1a. When this notification is detected by the add/drop control unit 7 of the communication control device 1a that is the source, the busy field BY of the packet PT is reset, and the packet is sent out to the transmission path as it is as a retransmission packet.

[Effect]

If a packet cannot be received due to lack of free space in the receive buffer memory, etc., the packet is sent back to the source with an indication that it cannot be received. Since the display is turned off and the packet is relayed and sent as a retransmitted packet, there is no need to store a copy of the sent packet at the source, and the loop-shaped transmission path itself can be used as a buffer memory function.

〔Example〕

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

FIG. 2 is a block diagram of an embodiment of the present invention, in which 4 is a selector, 5 is a reception buffer memory, 6 is a synchronization circuit, 7 is a branch/add control section, 8 is a transmission buffer memory, 9 is a delay circuit, and 1o is a The input terminal of bucket a transmitted via the transmission line is an output terminal 11 for sending packet b to the transmission line. An example of the configuration of packet a applied to the input terminal 10 is shown in FIG. 3. The packet consists of a header and data. It consists of a field C, a destination address field DA, and a source address field SA.

In the header of the transmitted packet, the packet valid/invalid field P indicates valid, the receive busy field BY indicates not busy, and the control field C contains control information such as the packet type and packet length. , the destination address field DA indicates the address of the terminal device to which the packet is to be transmitted or the communication control device including this terminal device, and the source address field SA indicates the address of the communication control device of the source or the address of the terminal device of the source. This indicates the address of the communication control device included.

The packet a applied to the input terminal 10 is synchronized by the synchronization circuit 6, and the packet a is sent to the drop/add control unit 7 as valid/valid.
Identification is made as to whether it is invalid or addressed to the own device. That is, it is determined whether the received packet a is valid or invalid based on the contents of the packet valid/invalid field P, and whether it is addressed to the device itself is determined based on the contents of the destination address field DA. Also, it is determined whether the packet is sent from the own device or not based on the contents of the source address field SA.

When the received packets are accumulated and there is no free space, the reception buffer memory 5 notifies the branch/insertion control unit 7 with a reception impossible signal C that no more reception packets can be written.

Therefore, when it is determined that the reception bucket (a) is valid and addressed to the device itself, and the reception buffer memory 5 is capable of receiving, the reception instruction signal d is added to the reception buffer memory 5, and thereby, The reception bucket a) is written into the reception buffer memory 5. Then, the control signal f from the drop-and-insert control unit 7 is applied to the selector 4 and the transmission buffer memory 8, and the selector 4 transmits the data in place of the bucket) a via the delay circuit 9, for example, when there is a transmission request. Select packet g from buffer memory 8. Therefore, the bucket )g is sent from the output terminal 11 to the transmission path as a transmission packet b.

On the other hand, as before, even when the drop-and-insert control unit 7 identifies that the received packet a is valid and addressed to its own device, if the unreceivable signal C is added, the drop-and-insert control unit 7 receives the reception instruction signal. It outputs a reception busy signal e without outputting signal d. Then, the selector 4 is switched and controlled by the control signal f. The selector 4 sets the reception busy field BY of the packet a via the delay circuit 9 as reception busy, selectively outputs the packet a, and sends it from the output terminal 11 to the transmission path as a transmission packet b. That is, the packets that could not be received are sent out with their reception busy field BY set to busy.

In the transmission source communication control device, the branch/insertion control unit 7 identifies the validity/invalidity of the reception bucket a), whether it is addressed to the device itself, or whether it is sent from the device itself. . As described above, a packet that cannot be received due to reception busy can be identified as a packet sent from the device itself by the contents of its source address field SA, and at that time, the contents of the reception busy field BY are identified. If the reception busy field BY is set to busy, the destination communication control device determines that the packet could not be received, resets the reception and busy field BY, and sends the packet as is through the selector 4. The packet is then sent from the output terminal 11 to the transmission line as a retransmission packet.

Therefore, packets that cannot be received by the destination communication control device can be retransmitted with simple processing. Of course, this retransmission process can be repeated until the destination communication control device receives it.

In addition, if the destination communication control device is in trouble, the reception busy field BY is returned to the source communication control device in a state where it is not busy, so it can be distinguished from the case where it is normal and reception is not possible. In this case, the communication control device of the source will erase this packet.

Such control simplifies packet retransmission processing and prevents packets from permanently circulating on the transmission path due to failure in reception.

〔Effect of the invention〕

As explained above, the present invention provides a communication control device designated by a destination address field DA, etc., in a loop transmission network that performs packet transmission.
If you cannot receive packets because there is no space available,
The receive busy field BY is used to notify the sender's communication control device that the packet cannot be received, and the sender's communication control device that receives this notification resets the receive busy field of the packet and sends it as a retransmission packet. Therefore, the loop transmission path functions as a buffer as it is, and the source communication control device does not need to store a copy of the sent packet, and can retransmit the packet in a short time with simple processing. It has the advantage of being able to send out

[Brief explanation of drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is an explanatory diagram of the structure of a packet, and FIG. 4 is an explanatory diagram of a loop transmission network. IA to LD, la, and Ib are communication control devices, 2 is a transmission path, 3 is a terminal device, 4 is a selector, 5 is a reception buffer memory, 6 is a synchronization circuit, 7 is a drop/add control unit, 8 is a transmission buffer memory, 9 is a delay circuit, 10 is an input terminal, 11 is an output terminal, P is a packet valid/invalid field, BY is a reception busy field, C is a control field, DA is a destination address field, and SA is a source address field.

Claims (1)

[Claims] A communication control device (1) that controls communication between terminal devices is connected in a loop through a transmission path (2), and communication data between the terminal devices is packetized and the communication control device (1) ), when the communication control device (1) fails to receive a transmitted packet, it notifies the source communication control device using the packet, and A packet retransmission control method characterized in that, when the communication control device detects the notification, the communication control device relays the packet as a retransmission packet as it is.