JPH0697983A - Network system - Google Patents

Abstract

PURPOSE:To perform flow control so as not to generate the frame overflow of a buffer in a data link layer in a network system. CONSTITUTION:In the node of the network system, a frame received at a physical layer interface 23f is stored in a reception buffer 23e. A buffer using amount monitoring circuit 23h checks the number of the frames inside the reception buffer 23e for each frame reception and generates buffer full signals when the checked number of the frames is more than the preset number of the frames. When the buffer full signals are received, a protocol controller 23b sets a transmission cancellation frame at a transmission buffer 23d and instructs transmission to the physical layer interface 23f. Also, when the number of the frames of the reception buffer 23e is less than the prescribed number of the frames, buffer empty signals are generated and a transmission starting frame is transmitted corresponding to the buffer empty signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a network system having a plurality of nodes and a transmission path interconnecting the nodes and transmitting / receiving a frame between the nodes.

[0002]

BACKGROUND OF THE INVENTION Frame switched networks, especially
In the field of local area networks (LANs), flow control is required to perform control between a transmission terminal and a reception terminal so that a frame does not overflow in a reception buffer when receiving a frame. When the receiving terminal receives more frames than the reception processing capacity, the frames corresponding to the number of frames exceeding the number of frames that can be received are discarded and the receiving terminal requests the transmitting terminal to retransmit the frames. There is. Conventionally, such flow control has been performed in a portion corresponding to the transport layer of the OSI (open system interconnection) reference model. In this transport layer, buffers are managed for each logical channel of communication, and flow control is performed so that frame overflow does not occur in each buffer.

[0003]

However, the flow control for each logical channel in the transport layer has a problem that it is impossible to prevent the frame overflow of the buffer in the data link layer where the channel cannot be identified.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a network system capable of performing flow control so that frame overflow of a buffer does not occur in a data link layer.

[0005]

In the network system of the present invention, a plurality of nodes for transmitting and receiving frames,
In a network system having a transmission path that interconnects each node, each node stores in the storage unit a transmission / reception unit that transmits / receives a frame to / from another node, a storage unit that stores the frame received by the transmission / reception unit. A check unit for checking the number of stored frames, and a generating unit for generating a transmission stop frame for requesting another node to stop frame transmission according to the number of frames stored in the storage unit. The generated transmission stop frame is transmitted to another node by the transmission / reception means, and the other node receiving the transmission stop frame stops transmitting the frame to the node that transmitted the transmission stop frame.

[0006]

With the above-described structure, the flow control is performed so that the frame overflow of the buffer in the data link layer does not occur, so that unnecessary frame retransmissions in the transport layer are reduced. Therefore, the frame transfer time is shortened. In addition, since the number of retransmitted frames is reduced, the capacity of the network can be efficiently used.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments of the present invention, a node of a conventional network system will be described with reference to FIG. In FIG. 8, a conventional node is a CPU (centra
lprocessing unit) 10, memory 11, control bus 1
2, the network interface 13, and the transmission path 14.

The network interface 13 includes a bus interface 13a and a protocol controller 1.
3b, memory 13c, transmission buffer 13d, reception buffer 13e, physical layer interface 13f, and internal bus 13g. The internal bus 13g includes a bus interface 13a and a protocol controller 1
3b, the memory 13c, the transmission buffer 13d, the reception buffer 13e, and the physical layer interface 13f are used for interconnection.

The physical layer interface 13f receives the frame transmitted from another node to its own node by judging the electric signal on the transmission path 14. The reception buffer 13e stores the frame received by the physical layer interface 13f.

The protocol controller 13b reads the frame stored in the reception buffer 13e, performs the protocol processing on the read frame, and the CPU 1
The result data indicating the processing result is transferred to 0.

Further, the protocol controller 13b is
In response to a frame transmission request output from the CPU 10,
The transmission information stored in the memory 11 is transmitted to the control bus 12,
It is transferred to the transmission buffer 13d via the bus interface 13a and the internal bus 13g, protocol information is added to this transmission information, and the physical layer interface 13f is added.
To instruct the frame transmission. As a result, the transmission information to which the protocol information is added is output from the physical layer interface 13f to the transmission path 14 as a transmission frame.
Next, examples of the present invention will be described.

FIG. 1 is a block diagram showing a configuration of a node of a network system which is an embodiment of the present invention. As shown in FIG. 1, this node includes a CPU 20 and a memory 2.
1, control bus 22, network interface 2
3 and the transmission line 24.

The network interface 23 includes a bus interface 23a and a protocol controller 2
3b, memory 23c, transmission buffer 23d, reception buffer 23e, physical layer interface 23f, internal bus 2
3g, and a buffer usage monitoring circuit 23h. That is, in this embodiment, the buffer usage monitoring circuit 23h is newly provided as compared with the node of the conventional network system shown in FIG. The internal bus 23g includes the bus interface 23a,
It is used for interconnecting the protocol controller 23b, the memory 23c, the transmission buffer 23d, the reception buffer 23e, the physical layer interface 23f, and the buffer usage monitoring circuit 23h. The physical layer interface 23f receives the frame transmitted from another node to its own node by determining the electric signal on the transmission path 24.

FIG. 2 is a diagram showing the structure of a frame (received frame) received by the physical layer interface 23f. As shown in FIG. 2, the received frame includes a header (H) 30, a destination address (DA) 31, a source address (SA) 32, information (INFO) 33, and an error detection code (FCS) 34. .

When the destination address 31 in the received frame is the own node address, that is, when the received frame is a frame transmitted to the own node, the received frame is stored in the receive buffer 23e by the physical layer interface 23f. It is stored in an empty area that is not stored.

On the other hand, the destination address 31 in the received frame
Is an address other than the own node address, that is, if it is not a frame transmitted to the own node, the received frame is discarded by the physical layer interface 23f.

The receiving buffer 23e is logically constructed by an identification area 40 and a data area 41, as shown in FIG. The identification area 40 and the data area 41 each have a plurality of areas.

When the physical layer interface 23f receives a frame addressed to its own node, the physical layer interface 23f stores the received frame in a predetermined area of the data area 41 of the reception buffer 23e and writes "1" in the corresponding area of the identification area 40. . Also, the physical layer interface 23f writes “0” in the corresponding area of the identification area 40 when the frame is read from the data area 41 of the reception buffer 23e.

The buffer usage monitoring circuit 23h counts the number of "1" written in each area of the identification area 40 for each frame reception. The frame storage status of the reception buffer 23e can be grasped from this count value.

Here, the frame transmission processing in the protocol controller 23b will be described with reference to FIG. 4. FIG. 4 is a flowchart showing the frame transmission processing in the protocol controller 23b of the node which is the embodiment of the present invention shown in FIG.

In FIG. 4, in step A1, the CPU
It is determined from 20 whether there is a frame transmission request. When there is a frame transmission request from the CPU 20 in step A1, it is determined in step A2 whether or not the physical layer interface 23f receives a transmission stop frame from another node.

FIG. 5 is a block diagram showing the structure of a transmission stop frame for requesting the transmission stop of a frame from another node. As shown in FIG. 5, the transmission stop frame includes a header (H) 40 and a destination address (DA) 4
1, source address (SA) 42, "transmission stopped" information 4
3 and an error detection code (FCS) 44.
The destination address 41 is set to the broadcast address, and the source address 42 is set to the own node address of the node transmitting the transmission cancel frame.

When a transmission stop frame from another node is received in step A2, it is determined in step A3 whether the physical layer interface 23f receives a transmission start frame from another node.

That is, when a transmission stop frame is received from another node during transmission of a frame to another node, transmission of the frame to another node is stopped. After that, when a transmission start frame is received from another node, frame transmission is restarted to the other node. Therefore, the transmission of the frame to the other node is stopped until the transmission start frame is received.

The structure of the transmission start frame is almost the same as the transmission stop frame shown in FIG. 5, and the transmission start frame includes "transmission start" information instead of "transmission stop" information 43.

When a transmission start frame is received from another node in step A3, the frame in the transmission buffer 23d is transmitted (step A4). That is,
The transmission information stored in the memory 21 is the control bus 2
2, bus interface 23a, and internal bus 23
It is transferred to the transmission buffer 23d via g, and protocol information is added to this transmission information. Further, the physical layer interface 23f is instructed to transmit the frame. As a result, the transmission information to which the protocol information is added is output from the physical layer interface 23f to the transmission path 24 as a transmission frame.

The CPU 20 may make a frame transmission request to a plurality of nodes to the protocol controller 23b. In this case, the frame transmission processing as described above is sequentially performed for each frame transmission request.

FIG. 6 shows, for example, that three nodes (destination A,
FIG. 7 is a diagram for explaining a procedure of frame transmission processing of a protocol controller 23b when a frame transmission request for B and C) is given from the CPU 20.

In FIG. 6, the time T1 is the destination A, B,
It shows the time when a frame transmission request for C is received from the CPU 20. Therefore, the protocol controller 23
In b, first, the frame transmission to the destination A is started.

Time T2 indicates the time when the transmission stop frame is received from the destination A during the frame transmission to the destination A and the frame transmission to the destination B is started. Therefore, the frame transmission to the destination A is temporarily stopped according to the received transmission stop frame.

Time T3 indicates the time when the transmission start frame is received from the destination A and the frame transmission to the destination A is restarted. Therefore, the frame transmission to the destination A is restarted according to the received transmission start frame, and the frame transmission to the destination B is temporarily stopped.

Time T4 indicates the time when the frame transmission to the destination A is finished and the transmission to the destination B is restarted. Time T5 indicates the time when the frame transmission to the destination B is ended and the frame transmission to the destination C is started. Time T6 indicates when the frame transmission to the destination C is finished.

As described above, the frame transmission processing is performed in order from the destination A. When the transmission stop frame is received during the frame transmission to the destination A, the frame transmission process shifts from the process for the destination A to the process for the destination B. After that, when the transmission start frame is received, the frame transmission processing is performed from the processing for the destination B to the destination A.
The process will be returned to. By such an operation, the frame transmission processing is performed from the destination A to the destination C.

In addition to the data frame frame transmission process as described above, a process of transmitting a control frame (transmission stop frame, transmission start frame) is further performed. Whether to transmit the control frame is determined every time one data frame is transmitted, and if necessary, the control frame is transmitted with priority over the data frame.

Next, the frame receiving process in the protocol controller 23b will be described with reference to FIG. 7. FIG. 7 is a flowchart showing the frame receiving process in the protocol controller 23b of the node which is the embodiment of the present invention shown in FIG.

In the protocol controller 23b, when the number of received frames is larger than the number of processable frames indicating the processing capability, the number of frames stored in the reception buffer 23e is large. When the number of frames stored in the reception buffer 23e exceeds the preset number of frames, the buffer usage amount monitoring circuit 23h generates a "buffer full" signal and outputs the "buffer full" signal to the protocol controller 23b. Output to.

Therefore, in step B1, it is determined whether this "buffer full" signal has been received. In step B1, if the "buffer full" signal is not received, it is determined that the reception buffer 23e has enough area to store the frame, and the next received frame in the physical layer interface 23f is stored in the reception buffer 23e. (Step B2).

On the other hand, when the "buffer full" signal is received in step B1, the transmission stop frame is set in the transmission buffer 23d, and the physical layer interface 23f is instructed to transmit the frame. As a result, the transmission stop frame set in the transmission buffer 23d is transmitted from the physical layer interface 23f to the transmission line 24.
Is broadcast (step B3).

When another node receives this transmission stop frame, frame transmission from the other node is stopped for the node indicated by the source address included in the received transmission stop frame. The frame transmission can be stopped as follows.

That is, when the protocol controller in another node determines that the received frame is the transmission stop frame, the source address included in the received frame is stored in the memory in the interface as the frame transmission stop node address. Here, when there is a transmission request from the CPU to the protocol controller, the destination address output from the CPU is compared with the frame transmission stop node address stored in the memory,
If the frame transmission stop node address that matches the destination address is stored in the memory, the frame transmission is stopped.

Since the node which has transmitted the transmission stop frame does not receive the frame from another node,
The frames stored in the reception buffer 23e are sequentially protocol-processed by the protocol controller 23b.

When the number of frames that can be stored in the reception buffer 23e becomes equal to or less than the preset number of frames, the buffer usage amount monitoring circuit 23h generates a "buffer empty" signal and outputs this "buffer empty" signal. Output to the protocol controller 23b.

Therefore, in step B4, it is determined whether this "buffer empty" signal has been received.
When the "buffer empty" signal is not received in step B4, it is determined that the reception buffer 23e does not have a sufficient area for storing the frame. Therefore, the frame stored in the reception buffer 23e is read, and the protocol processing is performed on the read frame (step B5). Result data indicating the result of the protocol processing is transferred to the CPU 20.

On the other hand, when the "buffer empty" signal is received in step B4, the transmission start frame is set in the transmission buffer 23d, and the physical layer interface 23f is instructed to transmit the frame. As a result, the transmission start frame is the physical layer interface 23f.
Is broadcast from the transmission line 24.

When another node receives this transmission start frame, the source address is read from the received transmission start frame, and the frame transmission stop node address that matches the read source frame is deleted from the memory. . As described above, frame overflow in the reception buffer 23e can be prevented.

In this embodiment, the transmission stop frame and the transmission start frame are used in order to prevent frame overflow in the reception buffer of each node. However, it is possible to control the frame overflow of the reception buffer by providing a timer in each node.

That is, when a predetermined node receives a transmission stop frame, a timer provided in the node is started, and frame transmission is stopped until the timer value of the timer reaches a preset timer value. This makes it possible to prevent frame overflow in the reception buffer of the node. Therefore, in this case, it is not necessary to transmit the transmission start frame to the predetermined node as compared with the above-described embodiment. Further, it is possible to prevent a situation in which the transmission start frame does not reach all the nodes and the frame cannot be transmitted forever.

Furthermore, when frame transmission is stopped using a transmission stop frame, information with a small amount of data such as control information is transmitted with a frame, and information with a large amount of data such as image information causes a buffer overflow. By making a decision not to send by the protocol controller, it becomes possible to always send only control information in a frame. The embodiment of the present invention has been described above,
The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the gist of the present invention.

[0049]

As described above, since the flow control is performed so that the buffer frame in the data link layer does not overflow, unnecessary frame retransmissions in the transport layer are reduced. Therefore, the frame transfer time is shortened. In addition, since the number of retransmitted frames is reduced, the capacity of the network can be used efficiently.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a node in a network system that is an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a received frame.

3 is a diagram showing a logical configuration of a reception buffer in the node shown in FIG.

4 is a flowchart showing a frame transmission process of a protocol controller in the node shown in FIG.

FIG. 5 is a diagram showing a structure of a transmission stop frame.

FIG. 6 is a diagram for explaining the procedure of frame transmission processing of the protocol controller when there are transmission requests from the CPU to three nodes.

7 is a flowchart showing a frame reception process of a protocol controller in the node shown in FIG.

FIG. 8 is a block diagram showing a configuration of a node in a conventional network system.

[Explanation of symbols]

20 ... CPU, 21 ... Memory, 22 ... Control bus, 23 ...
Network interface, 23a ... Bus interface, 23b ... Protocol controller, 23c ...
Memory, 23d ... Transmission buffer, 23e ... Reception buffer, 23f ... Physical layer interface, 23g ... Internal bus, 23h ... Buffer usage monitoring circuit, 24 ... Transmission path.

Claims (4)

[Claims] 1. In a network system having a plurality of nodes for transmitting and receiving frames and a transmission path for interconnecting the nodes, each node includes a transmitting and receiving means for transmitting and receiving frames to other nodes, and a transmitting and receiving means. Storage means for storing the received frames, check means for checking the number of frames stored in the storage means, and a request to stop frame transmission to another node according to the number of frames stored in the storage means The transmission stop frame thus generated is transmitted to another node by the transmission / reception means, and the other node receiving the transmission stop frame transmits the frame of the frame for the node transmitting the transmission stop frame. A network system characterized by stopping transmission. 2. The network system according to claim 1, wherein the frame transmission to the node that has transmitted the transmission stop frame from another node is stopped for a predetermined period. 3. The generation means further generates a transmission start frame requesting restart of frame transmission to another node according to the number of frames stored in the storage means, and transmits a transmission stop frame from the other node. 2. The network system according to claim 1, wherein the frame transmission to the node that has made the transmission is stopped until the transmission start frame is received from the node that has transmitted the transmission stop frame. 4. The network system according to claim 1, wherein the other node suspends transmission of only a predetermined amount of frames or more to the node which transmitted the transmission suspension frame.