JPH11239163A - Inter-lan flow control method and switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow control method and a switch for reducing the processing load on a frame relay suited to data transmission between LANs through a wide area network for which transmission delay is large and a transmission band is small compared to private branch communication by monitoring a data amount in a reception buffer and executing flow control in the case that a retained data amount exceeds a fixed value. SOLUTION: For the relation of the size of a buffer and respective parameter values, at the point of time at which the amount of data stored in the reception buffer exceeds a flow control start threshold value (FS) 41, the switch of a reception side LAN informs the switch of a transmission side LAN of the execution of the flow control. Whether or not the LAN is in flow control is displayed by a flow control flag. In the case that the amount of the data stored in the reception buffer becomes not more than a flow control release threshold value (FT) 42, the switch of the reception side LAN informs the switch of the transmission side LAN of the release of the flow control. At the time, the flow control flag is cleared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed LAN (local area network) having a transmission speed of 1 Gbps or more, such as a fiber channel or a gigabit Ethernet, and an STM1 dedicated line or an ATM network having a maximum transmission speed of 150 Mbps. The present invention relates to a flow control method and a switch between LANs when connecting to a wide area network and performing high-speed data transfer through the wide area network.

[0002]

2. Description of the Related Art In recent years, a high-speed network, such as a fiber channel or a gigabit Ethernet, which provides a gigabit class transmission speed to each end node has been introduced as a LAN in a business premises. These LANs
Includes a switching mechanism having a plurality of line ports and end nodes such as servers and computers connected to the switching mechanism. As this switching mechanism, switches of various topologies such as a star type, a loop type, a bus type, etc. are defined.
Flow control between a switch and a terminal is commonly defined. On the other hand, the flow control between the switches is specified for each topology.

For example, in the case of a fiber channel, a credit is defined as the number of frames that can be continuously transmitted without waiting for a response from the other party, and the number of transmission frames is increased by the number of response frames received from the other party. Control is adopted. In addition, in Gigabit Ethernet, when the occupation state of the buffer on the receiving side becomes a certain level or more and it becomes difficult to receive more data, the receiving side requests the transmitting side to suppress transmission for a certain period of time. Send a signal. The flow control for such a LAN presupposes that the transmission distance is as short as a few km to a maximum of 10 km, and that the transmission capacity is 1 Gbps and the communication environment in which frames and signals are transmitted via a broadband transmission path. Stipulated.

On the other hand, as for the line speed of the wide area network, at present, the maximum speed of a dedicated line is 150 Mbps,
Up to 135 Mbps on the network, the line speed of the above-mentioned premises (1 Gbps)
Smaller than. In addition, when an exchange is installed in a network such as a wide area ATM network, a data cell accumulation delay occurs in the exchange. When connecting between multiple LANs via a wide area network, the transmission distance may be up to 2,000 km, but due to the transmission delay associated with such long distance transmission and the storage delay in the switchboard, the transmission distance via the wide area network may be reduced. In data transmission, the transmission delay is significantly larger than in in-house communication. For example, in the case of optical fiber transmission, one-way transmission for 10 km on campus
50 μsec, but 20 msec via a wide area network
May be.

[0005] It is of course possible to improve the line speed of the wide area network with the advance of technology in the future. However, considering that the line usage fee of the wide area network becomes expensive in the case of the high speed line, the wide area line is slower than the campus. It is fully anticipated that the network line will continue to be used. Therefore, it is necessary to consider the flow control method via the wide area network as having a large data transmission delay and a small transmission band as compared with the communication in the premises.

On the other hand, communication protocols such as X.25 and HDLC have been conventionally used as typical flow control in communication via a wide area network. However, they have a large processing load of communication control and are mainly applied to low-speed communication such as at most several hundred kbps to several Mbps, and are not for high-speed communication at 100 Mbps or more.

In addition, as a flow control method between a computer and an input / output device, a simple flow control method for notifying the transmission from the receiving side to the transmitting side or notifying the release of the suppression from the receiving side to the transmitting side in accordance with the state of data retention in the receiving buffer However, if a simple method of suppressing and canceling such transmission is applied to a transfer through a wide area network having a large transmission delay, such suppression and suppression of cancellation of transmission are considered. It takes a long time to notify the user, and a decrease in throughput due to interruption of transmission between LANs cannot be avoided.

On the other hand, in recent years, the storage capacity and input / output speed of a storage device and the communication speed of a computer have been improved, and as described above, high-speed communication of several hundred Mbps to about 1 Gbps has become possible within a premises. For broadcasting systems and the like, transfer of video information of about 100 Mbps via a wide area network is being studied. Therefore, even in the LAN-to-LAN communication via the wide area network, 100 Mbps is not affected by the transmission delay in the wide area network.
The need for the above high-speed communication is increasing.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been made in consideration of the above-mentioned situation. Thus, the processing load of the frame relay is small, and the transmission delay is large and the transmission band is small as compared with the local area communication. It is an object of the present invention to provide a flow control method and a switch suitable for the data transmission of the above.

[0010]

According to the present invention, there is provided a method for controlling a flow between LANs, the method comprising the steps of:
Then, the congestion state is monitored by the occupied buffer amount of the data received from the wide area network, and when the occupied buffer amount of the received data is less than a certain value, the flow control is not performed, and the occupied buffer amount of the received data exceeds a certain value. In this case, the start of flow control is notified to the sending LAN, and if data is transferred from the receiving LAN to the receiving end node when the buffer becomes empty in the flow control execution state, the empty buffer amount is sent to the transmitting LAN. Notify, on the sending LAN, the receiving LAN
If there is no notification of flow control or notification of release of flow control from, data transfer is performed without controlling traffic, and if notification of start of flow control is received, the amount of data notified from the receiving LAN Is transmitted.

In such an inter-LAN flow control method according to the present invention, after the receiving LAN notifies the transmitting LAN of the start of flow control execution, the receiving LAN actually waits for a response from the transmitting LAN to the flow control execution start notification. And the maximum transfer data amount that can be transmitted from when the transmitting LAN receives the flow control execution start notification to when transmission is suppressed, and the data amount that is actually received by the receiving LAN. The difference is obtained, and if the actually received data amount is smaller than the maximum transfer data amount that can be transmitted by the transmission side LAN, the data amount of the difference is notified to the transmission side LAN, and the transmission side LAN transmits the notified data amount. Is desirably transferred.

According to the present invention, the receiving LAN
At the connection with the wide area network, the amount of data staying in the reception buffer is monitored, and if the amount of staying data is below a certain value, flow control is not performed, but if the amount of staying data exceeds a certain value, Perform flow control. Since the transmission bandwidth of the LAN is larger than the transmission bandwidth of the wide area network, if the receiving capacity of the receiving end node is high, data does not stagnate at the connection with the wide area network, so that flow control is not performed and the processor is not used. Used only for other transfer processing. Flow control is performed when the receiving capability of the receiving end node is reduced, or when traffic concentrates on a specific end node and data stays in the receiving buffer. Since the number of flow control frames to be used is smaller than in the conventional methods such as X.25 and HDLC, the processing load on the processor can be reduced.

As described above, since the processor processing load for flow control can be reduced as compared with the conventional method, the transfer throughput can be improved, and high-speed transfer between LANs via a wide area network becomes possible. Even during the execution of the flow control, the amount of data transmitted from the reception buffer of the reception LAN to the reception end node and released from the reception buffer of the LAN is notified to the transmission LAN as needed, and the data amount is transmitted to the transmission LAN. Is allowed, even if the data is transmitted through a wide area network having a large transmission delay, L
Communication between the ANs is performed without interruption, and the processor and the reception buffer can be used effectively to the maximum and the transfer throughput can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a network to which a flow control method between LANs and a switch according to the present invention are applied. The LAN 11 includes switches 12 and 13 and an end node 14 connected thereto. Depending on the size of the LAN, a plurality of switches may be used in the same LAN, and some switches 12 are connected to the wide area network 10. Between switches 12 and 13, between switches 13 and between switches 12, 13
And the end node 14 are connected by a LAN interface. For the flow control in these LAN interfaces, protocols specified in each LAN are applied.

The flow control of the present invention is used for data transfer between switches 12 via a wide area network 10. Currently provided wide area network line is up to 150Mbps, but LAN
Among them, the high-speed one has a speed of about 1 Gbps, which is overwhelmingly higher than the line speed of the wide area network 10. Normally, when data is transferred from a high-speed network to a low-speed network, flow control is required at the boundary of the network. In FIG. 1, a wide area network 10 is connected to an end node 14.
When data is transmitted at a transmission rate exceeding the line speed, the switch 12 performs flow control.

If the receiving capability of the receiving end node 14 is higher than the line speed of the wide area network 10 and the communication speed of the transmitting end node 14, data does not accumulate in the switch 12 of the receiving LAN. However, end node 14
In many cases, the processing of the processor is interposed in the reception processing of, and when the processor is used for other processing, the reception capability of the end node 14 may be reduced.

When the end node 14 is a server, a communication request may be issued from a plurality of end nodes to the server at the same time. In such a case, it is difficult to simultaneously perform communication in accordance with the communication speed of all end nodes that have issued a communication request to the server. As described above, when the reception capability of one end node does not reach the transmission speed required by the transmission-side end node, data remains in the buffer in the LAN switch.

In order to prevent data from remaining in the switch and increase data discarding in the switch,
Flow control is required at a portion where data flows from a wide area network to a LAN switch. As described above, even when the transmission speed of the LAN is overwhelmingly higher than the transmission speed of the wide area network, it is necessary to provide a flow control function on the assumption that the reception capability of the end node is reduced or the data traffic is concentrated. .

FIG. 2 is a diagram showing the configuration of the reception buffer 20 of the switch 12 for receiving a data frame from the wide area network. The reception buffer 20 stores data received from the wide area network 10 cyclically. The buffer block of the reception buffer 20 is configured to be sufficiently smaller than the maximum frame length of the reception data and to store the reception data in a buffer area without waste regardless of the frame length. In the figure, data is stored in the data storage portion 22, and 21
Is an empty area. The data frame received from the wide area network is stored in the buffer area specified by the next storage area pointer 27, and when transfer to the end node becomes possible, the data frame is specified by the next transfer frame pointer (P1) 25. The data is sequentially transferred from the data frame of the area. These pointers are updated each time the switch receives a data frame from the wide area network or transfers a data frame to an end node.

FIG. 3 is a diagram showing the relationship between the buffer size and each parameter value. When the amount of data stored in the reception buffer exceeds the flow control start threshold (FS) 41, the switch 12 of the receiving LAN notifies the switch 12 of the transmitting LAN of execution of flow control. Whether or not the LAN is executing flow control is indicated by a flow control execution flag (reception direction) 23 (FIG. 2). When the amount of data stored in the reception buffer 20 becomes equal to or less than the flow control release threshold (FT) 42, the switch 12 of the reception LAN is set to the transmission L
The switch 12 of the AN is notified of the release of the flow control. At this time, the flow control execution flag (reception direction) 23 is cleared.

FIG. 4 is a diagram showing a sequence of data frame transmission / reception between LANs and a flow control frame transfer sequence based on the amount of data stored in the reception buffer. FIG.
FIG. 3 is a diagram showing a configuration of a flow control frame transmitted and received between LANs, and includes a control header 50, a command type 51, and an additional window size 52. In the flow control frame, the amount of data in the reception buffer indicates the flow control start threshold (FS) 41.
Flow control start notification frame for notifying the sending LAN of the start of flow control when the number exceeds the limit, a response frame from the sending LAN for the flow control start notification, and addition for notifying the addition of the transmission window size during the execution of flow control A window notification frame and a flow control release notification frame for notifying the transmitting side LAN of release of flow control when the amount of data in the reception buffer becomes equal to or less than the flow control release threshold (FT) 42 are included. Indicates these types.

[0022] The additional window notification frame is
This is used for notifying the transmitting LAN of the amount of data in the portion where the receiving buffer becomes empty by transmitting a frame from the AN to the end node as an additional transmission window. The transmission of the additional window notification frame is performed every time a fixed amount of data is transmitted to the end node.
In FIG. 2, at the start of flow control, the previous frame pointer (P
0) The contents of 24 are set to 0. The switch 12 of the receiving LAN updates the next transfer frame pointer (P1) 25 every time a data frame is transferred to the end node. When the difference between the next transfer frame pointer (P1) 25 and the previous frame pointer (P0) 24 exceeds a certain value, the switch 12 transmits the difference (P1-P0) as an additional transmission window by using an additional window notification frame. Notify the local LAN.

When transmitting the additional window notification frame, the switch 12 of the receiving LAN sets the value of the next transfer frame pointer (P1) 25 at that time to the previous frame pointer (P0) 24. Thereafter, the monitoring of the transmission data amount to the end node and the transmission of the additional window notification frame to the transmission side LAN are executed until the flow control is released.

FIG. 6 is a diagram showing a configuration of the transmission buffer 30 for storing a data frame for transmission to another LAN. The transmission buffer 30 is used as a buffer when transmitting a data frame in a direction from the LAN to the wide area network, and cyclically stores the frame transmitted from the transmitting end node. In the figure, data is stored in a data storage portion 32, and 31 is a free area. The head of the data frame to be transferred from the transmission buffer 30 to the wide area network is designated by the next transmission frame pointer 35. The storage position of the data frame transferred from the end node to the switch 12 is specified by the next storage buffer pointer 36.

The switch 12 of the transmission side LAN is connected to the reception side LA
When a flow control start notification frame is received from N, the flow control execution flag 33 is set. The flow control execution flag 33 is cleared when a flow control release notification frame is received from the receiving LAN. While the flow control execution flag 33 is set, the switch 12
Transmits only the data amount set in the transmission window size 34. The transmission window size 34 is initialized to 0 when a flow control start notification frame is received. Thereafter, each time an additional window notification frame is received from the receiving LAN, the additional window size 52 (FIG. 5) in the additional window notification frame is changed to the transmission window size.
Add to 34.

In the transmission-side LAN, the transmission data amount is subtracted from the transmission window size 34 every time a data frame is transmitted to the wide area network. Thus, the transmission-side LAN transmits data corresponding to the window size notified from the reception-side LAN until the transmission window size 34 becomes zero. When the flow control is released, the data frame is transmitted with the transmission window size set to infinity until a flow control start notification frame is received from the receiving LAN.

As shown in FIG. 3, when the amount of data in the reception buffer exceeds the flow control start threshold value 41, the reception side L
The AN transmits a flow control start notification frame, but the maximum Rmax = (transfer rate of wide area network line) × by the time the other LAN receives this frame and suppresses data transfer.
(One-way transmission delay time of wide area network) × 2 data may be received.
A reception buffer having a size obtained by adding Rmax to 41 is provided. When the data amount (RD) received during the round-trip transmission delay time of the wide area network is smaller than this Rmax, the remaining buffer amount (AD) is used in the receiving LAN to make the remaining buffer amount (AD) usable. As an additional window size to the transmission side LAN.

After the flow control is started, the amount of data (RD) received during the round-trip transmission delay time of the wide area network is, as shown in FIG. After transmitting the notification frame, it is calculated from the amount of data received until a flow control response is received from the transmitting LAN. In this case, the receiving LAN is R
The transmission side LAN is notified of max-RD = AD as an additional transmission window size. On the sending LAN, this additional sending window size is added to the sending window size 34,
This data is transmitted. In this way, the difference between the maximum received data amount predicted at the start of flow control and the actually received data amount is obtained, and the difference data can be newly transmitted, so that the entire reception buffer can be used effectively. ing.

The RD in FIG. 3 is the amount of data transferred to the end node on the receiving LAN since the start of flow control (the difference between the previous frame pointer (P0) 24 and the next transfer frame pointer (P1) 25 in FIG. 2). Is calculated by a counter of the transfer data amount integrated value (D) 26 (FIG. 2). As described above, the effective use of the reception buffer increases the transmission window size of the transmission-side LAN, improves the transfer throughput, and reduces the probability of data discard by storing more data in the buffer. , Communication reliability can be increased.

The flow control method of the present invention is different from the conventional method in which a transmission sequence number is added to a data frame and flow control is performed by a combination of the transmission sequence number and a transmission window fixed in advance. There is no need to change the content of Therefore, in the switch 12 located at the connection with the wide area network, a high-speed dual port memory is used for relaying data frames from the LAN to the wide area network, and the processor accesses the high speed dual port memory. This eliminates the need and eliminates memory access contention between the processor and other transfer control hardware in data frame transfer processing, reduces the memory access time for transfer, and speeds up transfer control.

FIG. 7 is a diagram for explaining a configuration example of the switch 12 of the present invention. In the figure, 60 is a processor unit, 61 is a program storage memory, 62 is a control memory, 63 is a LAN line control unit, 64 is a high-speed dual port memory, and 65 is a wide area network line control unit. The processor unit 60 monitors the congestion state based on the buffer amount. When the occupied buffer amount of the received data exceeds a certain value, the processor unit 60 activates the notification of the flow control execution start, and based on this, the wide area network line control unit 65
Forwards the notification frame. In the flow control execution state, the processor unit 60 calculates the amount of free buffer generated by the data transfer from the receiving LAN to the receiving end node, and the wide area network line control unit 65 transfers the notification frame based on the calculation. .

After notifying the transmitting LAN of the start of flow control execution, the processor unit 60 waits for a response from the transmitting LAN to the flow control execution start notification based on the buffer usage in the high-speed dual port memory 64. In addition, the data amount actually received is calculated, the difference from the maximum transfer data amount during the period is calculated, the notification to the transmission side LAN is started, and based on this, the wide area network line control unit 65 adds the additional window. Forward the notification frame.

In the transmission state, the wide area network line controller 65 controls the transmission data amount to the data amount notified from the receiving LAN. Further, the wide area network line control unit 65 controls the transmission data amount to the data amount notified from the receiving LAN by the additional window notification.

[0034]

As described above, in the flow control method of the present invention, the receiving capability of the end node is large,
When data does not accumulate in the LAN, the flow control is not performed, so that the processing load on the processor can be extremely reduced. Further, even when data stays in the LAN, it is necessary to notify the transmitting LAN of the amount of data transferred from the receiving LAN to the end node, and to allow the transmitting LAN to transmit a corresponding amount of data. Accordingly, even in communication via a wide area network with a large transmission delay, data transfer does not stagnate, so that communication can be performed without reducing transfer throughput. In recent years, high-speed LANs with a transmission speed of about 1 Gbps such as Fiber Channel and Gigabit Ethernet have been introduced.
By applying the flow control method of the present invention, it has become possible to connect these high-speed LANs via a wide area network and realize high-speed communication while avoiding congestion and maintaining reliability.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a network to which an inter-LAN flow control method and a switch according to the present invention are applied;

FIG. 2 is a diagram illustrating a configuration of a reception buffer of a switch that receives a data frame from a wide area network.

FIG. 3 is a diagram illustrating a relationship between the size of a reception buffer and each parameter value.

FIG. 4 is a diagram showing a sequence of transmitting and receiving a data frame between LANs and transferring a flow control frame based on the amount of data staying in a reception buffer.

FIG. 5 is a diagram showing a configuration of a flow control frame transmitted and received between LANs.

FIG. 6 is a diagram illustrating a configuration of a transmission buffer that stores a data frame for transmission to another LAN.

FIG. 7 is a diagram illustrating a configuration example of a switch according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Wide area network 11 LAN 12 and 13 Switch 14 End node 20 Reception buffer 21 Free space 22 Data storage part 23 Flow control execution flag 24 Previous frame pointer 25 Next transfer frame pointer 26 Transfer data amount integrated value 27 Next storage area pointer 30 Transmission Buffer 31 Free area 32 Data storage part 33 Flow control execution flag 34 Transmission window size 35 Next transmission frame pointer 36 Next storage buffer pointer 40 Reception buffer size 41 Flow control start threshold 42 Flow control release threshold 50 Control header 51 Command type 52 Addition Window size 60 Processor unit 61 Program storage memory 62 Control memory 63 LAN line control unit 64 High-speed dual-port memory 65 Wide area network line control unit

Claims (4)

[Claims] When performing data transfer between a plurality of high-speed LANs connected to each other via a wide area network, a receiving side LA is used.
At N, the congestion state is monitored based on the occupied buffer amount of the data received from the wide area network. If the occupied buffer amount of the received data is less than a certain value, the flow control is not performed, and the occupied buffer amount of the received data exceeds a certain value. In this case, the start of flow control is notified to the sending LAN, and if the buffer becomes empty due to data transfer from the receiving LAN to the receiving end node in the flow control execution state, the amount of free buffer is sent to the transmitting LAN. On the transmitting side LAN and the receiving side LA
If there is no flow control notification from N or a notification of flow control cancellation is received, data transfer is performed without controlling traffic, and if a flow control execution start notification is received, data notified from the receiving LAN is received. An inter-LAN flow control method, comprising transmitting data corresponding to an amount. 2. After the receiving LAN notifies the transmitting LAN of the start of flow control execution, the receiving LAN integrates the amount of data actually received until a response from the transmitting LAN to the flow control execution start notification is received. Calculates the difference between the maximum transfer data amount that can be transmitted from when the flow control execution start notification is received until the transmission is suppressed, and the data amount that is actually received by the receiving LAN. When the transmission data is smaller than the maximum transfer data amount that can be transmitted by the transmission LAN, the difference data amount is notified to the transmission LAN, and the transmission LAN transfers data corresponding to the notified data amount. 2. The inter-LAN flow control method according to claim 1. 3. A switch for connecting a LAN to a wide area network installed when data is transferred between a plurality of high-speed LANs connected to each other via the wide area network. Means for monitoring the congestion state based on the occupied buffer amount of the received data, means for notifying the transmission side LAN of the start of execution of the flow control when the occupied buffer amount of the received data exceeds a certain value, and Means for notifying the sending LAN of the empty buffer amount when a buffer is created due to data transfer from the receiving LAN to the receiving end node, and executing the flow control from the receiving switch during transmission to the wide area network. A switch including means for transmitting data corresponding to the data amount notified from the receiving LAN when a start notification is received. 4. A means for, after receiving from the wide area network, notifying the transmitting LAN of the start of flow control execution, and integrating the amount of data actually received until a response from the transmitting LAN to the flow control execution start notification. When the integrated data amount is smaller than the maximum transfer data amount that can be transmitted from when the transmission side LAN receives the flow control execution start notification to when the transmission is suppressed, the difference data amount is transmitted to the transmission side LAN. Notifying means, and transmitting to the wide area network, receiving LAN
4. The switch according to claim 3, further comprising means for transferring data corresponding to the data amount notified from the switch.