JP2000224180A - Data priority transfer method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data priority transfer method with which a large scale LAN network as a whole can maintain sufficient performance. SOLUTION: An inter-switch connection port sets priority of data transfer with respect by class to a terminal class and/or an information class and ensures a required throughput, independently of a traffic state as to communication with higher priority. Furthermore, a terminal connection port checks a length of a transfer frame queue to a receiver side terminal, and congestion is indicated to a data frame sent from the receiver side terminal when the length exceeds a prescribed length, and when the inter-switch connection port detects a congestion indication 43, the transmission priority of the data frame to the receiver side terminal is lowered. Or transmission may be restricted by delaying a return of a reply frame, depending on the frequency of reception of a frame to which the congestion display 43 is set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed local area network (high-speed LAN) constituted by interconnecting a plurality of switches having a transmission speed of 1 Gbit / s or more.
AN), by giving priority to data transfer according to the communication terminal and the importance of information, it is possible to guarantee real-time communication without lowering network performance,
The present invention relates to a method for transferring frames between switches in which traffic congestion on a specific port does not spread to other parts of the network.

[0002]

2. Description of the Related Art In recent years, a high-speed network, such as a fiber channel, which provides a gigabit class transmission speed to accommodation terminals has been introduced as a LAN in a business office.
The fiber channel network includes a switching mechanism having a plurality of line ports, and a terminal such as a server and a computer connected to the switching mechanism. When there are many terminals accommodated in the switching mechanism or when the distance between the accommodated terminals is large, a plurality of switches are connected to each other, and a larger-scale network is constructed. In the fiber channel, a variable-length frame of a maximum of 2 kbytes is transferred through a switch without connection. A destination terminal address is set in the frame, and the switch performs routing with reference to the destination address.

[0003] In Fiber Channel, flow control of link-by-link between adjacent nodes is specified. This flow control is performed based on the number of frames that can be continuously transmitted without waiting for a response signal called credit and the number of response signals from the partner device. For example, when the credit is 5, six consecutive frames are transmitted, and when three response signals are received, two (5-6 + 3) more frames can be transmitted. When all responses are received for the transmitted frames, frames for the number of credits can be further transmitted. Traffic regulation in a fiber channel network is performed, for example, when traffic is concentrated on a certain computer, or when a computer cannot receive all frames transmitted due to a low receiving capability of the computer. The side regulates frame reception by delaying the return of the response signal for flow control.

[0004] In the case of a fiber channel switch, it is configured to have an exchange capacity capable of exchanging all the traffic of the terminal to be accommodated. However, when a network is composed of a plurality of switches, the number of ports used for connecting the switches is limited. In many cases, traffic transferred between switches is limited, and it is not always possible to realize a throughput capable of transferring all traffic between terminals accommodated in a network. That is, in a large-scale network including a plurality of switches, congestion due to traffic concentration may occur at ports between switches where traffic from many terminals is multiplexed, even if frame transmission from the terminals is restricted.

Further, when traffic is concentrated on a terminal or when the receiving capacity of some terminals is reduced due to the load of a job executed on the terminal side, transmission to this terminal is restricted by traffic restriction from this terminal. Data is stored on the network. In this case, the switches execute flow control for frame reception restriction between the switches so that frames are not discarded. When the flow control is performed by one signal for all data frames between switches, if reception restriction occurs at one port of the network, reception is performed at all ports on the path from the source to the port that has performed reception restriction. Regulations arise,
Frame transfer to other terminals communicating via these ports is also restricted.

Conventionally, some fiber channel switches provide a transfer priority for each destination terminal. However, since the priority set for each terminal is fixed, a terminal having a higher priority has a higher priority. Even when reception restriction occurs due to traffic concentration, communication of other terminals is similarly affected. Also, in the conventional Fiber Channel switch, the priority of data frame transmission is assigned to each terminal, so if data frames stay in the network, real-time communication such as video and audio can be performed with low delay. Necessary data is also delayed without being distinguished from other data, and service is hindered.

[0007] In addition to performing flow control between the switch terminals or between switches based on the number of credits and response signals, a congestion situation in the network is notified to the transmission side, and traffic restriction is performed on the transmission side, thereby reducing network congestion. As a measure to alleviate this, ABR (Available
Bit Rate) is specified. In ABR, when a plurality of logical channels are set on a line, and when congestion is detected on a line port, a congestion indicator is set in the header of data transferred in the reverse direction to transmit the occurrence of congestion. By notifying the transmission side terminal, and reducing the transmission band of the logical channel on the path where congestion has occurred at the transmission side terminal,
Reduce congestion.

[0008]

As described above,
In networks such as conventional Fiber Channel, there is a mechanism to avoid frame discard at the time of congestion by flow control using credit, but the priority is fixed and there is an effective control mechanism to avoid congestion itself. Not. Further, in the conventional ABR, since the traffic regulation is performed at the transmitting terminal, it cannot be said that this is an effective means when the network becomes large-scale.

An object of the present invention is to provide a data priority transfer method capable of maintaining sufficient performance in a large-scale LAN network in view of the above problems.

[0010]

In order to achieve the above object, the data priority transfer method of the present invention sets a data transfer priority for a terminal type and / or an information type at an inter-switch connection port. When transferring high-priority communication in real time, a throughput required for the high-priority communication is ensured irrespective of the traffic state of the local area network.

In the data priority transfer method of the present invention, the length of the transfer frame queue for storing the transmission data to the receiving terminal is checked at the terminal connection port. Sets a bit indicating congestion in a data frame transmitted from the receiving terminal when exceeds a certain value, and when the congestion display is detected at the switch-to-switch connection port, the data frame to the receiving terminal is Lower the transfer order.

A credit indicating the number of frames that can be continuously transmitted is defined, a difference between the number of transmitted frames and a response frame is set with an upper limit value to perform flow control, and a transmitting terminal of a data frame whose transfer order is lowered is set. Continuously transmits data frames, the reception frequency of the frames for which the congestion indication is set among the frames transferred from the receiving terminal to the port of the terminal connection switch connecting the transmitting terminal The transmission of the response frame to the transmitting terminal may be delayed to restrict the transmission to the transmitting terminal.

Further, after the data frame of the congestion indication is first received from the terminal connection port at the inter-switch connection port, the presence or absence of frame transmission to the receiving terminal on which the congestion is indicated is monitored, and the monitoring is performed for a certain period. When there is no frame to be transmitted to the receiving terminal, the order of transmitting frames to the receiving terminal may be restored at the inter-switch connection port.

[0014] Further, when the terminal connection port receives a frame in which the congestion indication is set from the receiving terminal that controls traffic, even if the route differs depending on the communication direction, the transmitting terminal is connected. A congestion indicator may be set in a header of a frame to be transferred to the receiving terminal by a switch that is present, and congestion may be notified to a switch on a transfer route from the transmitting terminal to the receiving terminal.

In the present invention, the throughput required for high-priority communication is ensured at the inter-switch connection port, and the priority of the transfer frame is dynamically changed at the inter-switch connection port. The terminal connection switch for connecting the transmitting-side terminal controls traffic on the transmitting-side terminal by credit-based flow control, thereby preventing network congestion.

[0016]

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 local area network 11 in which a plurality of switches 12 are connected to each other. In the local area network 11, a terminal 13 is connected to the switch 12. Generally, a server 14 for data management and input / output is connected to the network,
The server 14 is shared and accessed by a plurality of terminals 13.

If a plurality of terminals 13 access the server 14 at the same time and traffic concentrates on the server 14, the server 14 cannot process all the processing requests from the terminals, and if a frame stays in the network, Congestion occurs. Further, even in a situation where all the terminals can process received frames without delay, even if traffic exceeding the line transmission capacity is concentrated on an inter-switch port (for example, port 15 in FIG. 1) that multiplexes traffic of a plurality of terminals. Also, a frame stays in a part of the switch of the network, and congestion occurs. As described above, even when a frame stays in a part of the switch, the discard of the frame can be prevented by the flow control between the switches using the credit. However, since there is a limit to the data buffer held by the switch, there is no free buffer for storing data frames of other terminals passing through the line port, and traffic passing through the line port may be reduced, resulting in congestion. is there.

In the present invention, a frame transfer priority is set for an information type at a switch-to-switch port (for example, 15 in FIG. 1), and real-time transfer of video, audio, etc. is performed in accordance with the priority of the frame type and the terminal type priority. For necessary information, a high priority is assigned to guarantee the transmission band, and high-priority video, audio, etc. are transferred irrespective of the network traffic situation.

FIG. 2 is a diagram for explaining one case of the data priority transfer method according to the present invention, in which a frame stays in a network due to traffic regulation of a receiving terminal at a certain line port. . When the terminal 21 regulates the reception traffic, the frame stays in the switch 31 to which the terminal 21 is connected. At this time, switch
At 31, the congestion indicator 43 is set in the header 42 of the frame 41 transmitted from the terminal 21. When the switch 32 connected to the switch 31 detects the congestion indication 43, the switch 32 lowers the priority of the frame transferred to the terminal 21. As a result, traffic to another terminal that does not perform the reception restriction, for example, the terminal 22, is transferred without being restricted by the reception restriction of the terminal 21. When the frame 41 on which the congestion display 43 is set in the switch 31 arrives at the switch 33 connecting the terminal 23 transmitting the frame to the terminal 21, the switch 33 transmits the frame to the terminal 21. For the terminal 23, the transmission of frames is regulated by flow control using credit. As a result, traffic to the terminal 21 decreases, and the terminal 21
Since the number of frames addressed to is reduced, network congestion is released.

FIG. 3 is a diagram for explaining another case of the data priority transfer method according to the present invention, in which the transfer route of a frame differs between the same terminals depending on the transfer direction. The arrow in the figure indicates the frame transmission direction. When a frame is transferred from the terminal 23 to the terminal 21 via the switch 34 instead of the switch 32, it is necessary to notify the switch 34 that the terminal 21 is performing traffic regulation.
When the switch 33 receives the frame 41 in which the congestion indicator 43 is set, the switch 33 sets the congestion indicator 45 in the header 46 of the frame 44 addressed to the terminal 21 from the terminal 23 and transfers the same. The switch 34 can know from the congestion display 45 set in the frame 44 that the terminal 21 is performing traffic regulation. Congestion display 43 (Fig. 2) and congestion display
Compared with 45, since the direction of the transfer frame to be set is different and the meaning of the information is also different, these congestion indications are set at different positions in the frame header.

FIG. 4 is a diagram showing an example 51 of the priority control table managed by the switch 32. The priority control table 51 includes an information type priority table indicating the priority of each information type.
52 and a terminal priority table 53 indicating the frame transfer priority of the terminal for each terminal address. The switch 32 performs the priority control of the frame transfer based on the information of the priority control table. In the information type priority table 52, for example, for real-time transfer, a high priority is set for video and audio for which it is necessary to guarantee a constant transmission band at all times. The switch 32 first refers to the information type priority table 52, and preferentially transfers a frame of an information type with a higher priority. This makes it possible to guarantee the transmission band for specific information regardless of the reception status of the terminal and the traffic status of the network. Next, for general information having a lower priority, the terminal refers to the terminal priority table 53 and transfers frames based on the priority assigned to each terminal.

For this priority transfer, the switch 32 provides a plurality of frame transfer queues for each priority level, and connects the frames to the frame transfer queues according to the priority. FIG. 5 shows an example of the header information of the frame 42 referred to by the switch 32 to determine the frame transfer priority.
The destination terminal address 61 indicates the address of the destination terminal of the frame. The information type 62 indicates the type of user data (video, audio, general data, etc.) stored in the frame. When the switch 32 receives the notification of the occurrence of the reception restriction of the terminal 21 from the switch 31 connected to the terminal 21, the switch 32 lowers the priority of the frame transfer addressed to the terminal 21 set in the terminal priority table 53. After lowering the priority in this way, the switch 32 monitors the traffic of the frame addressed to the terminal 21 and, for example, the number of frames addressed to the terminal 21 connected to the frame transfer queue of the switch 32 becomes equal to or less than a certain value. In this case, the priority is raised again to recover the transfer throughput of the frame addressed to the terminal 21.

[0023]

In a high-speed network currently used, such as Fiber Channel or Gigabit Ethernet, if all terminals are accommodated in one switch (up to 16 terminals can be accommodated at present), the Due to the large exchange capacity, high-speed data exchange can be realized without stagnation of frames. However, when configuring a network by connecting a plurality of switches in multiple stages in order to increase the number of accommodated terminals, depending on the configuration of the network, traffic concentrates on a specific switch connection port, and congestion on this port causes network traffic. Overall performance may be degraded. According to the data priority transfer method of the present invention, it is possible to prevent the restriction from a specific terminal or the congestion on an inter-switch connection port from affecting the transfer throughput of another terminal, thereby maintaining the performance of the entire network at a high level. Therefore, it is easy to construct a large-scale network using a plurality of switches, and the method of the present invention is extremely effective for increasing the size of a network that will be required in the future as information communication expands. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a local area network in which a plurality of switches are mutually connected.

FIG. 2 is a diagram for explaining one case of a data priority transfer method according to the present invention.

FIG. 3 is a diagram for explaining another case of the data priority transfer method according to the present invention.

FIG. 4 is a diagram illustrating an example of a priority control table managed by a switch.

FIG. 5 is a diagram illustrating an example of header information of a transfer frame.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Local area network 12 Switch 13 Terminal 14 Server 15 Inter-switch port 21, 22, 23 Terminal 31, 32, 33, 34 Switch 41, 44 Frame 42, 46 Header 43, 45 Congestion display 51 Priority control table 52 Information type priority table 53 Terminal priority table 61 Destination terminal address 62 Information type 63 Congestion display

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K030 GA03 GA13 HA10 HB17 HC14 KX11 LA03 LC01 LC11 LD11 LE05 MA13 MB15 5K033 BA04 CB06 CB18 DA14 DA15 DB03 DB13 9A001 BB04 CC08 DD10 JJ18 LL09

Claims (5)

[Claims] In a data priority transfer method in a local area network including a plurality of switches connected to each other, a terminal type and / or
Or, when the priority of data transfer is set for the information type and the high-priority communication is transferred in real time, the throughput required for the high-priority communication is ensured regardless of the traffic condition of the local area network. A data priority transfer method. 2. A terminal connection port checks the length of a transfer frame queue for storing data to be transmitted to a receiving terminal, and when the length of the transfer frame queue exceeds a certain value, transmission from the receiving terminal is performed. Setting a bit indicating congestion in a data frame to be transmitted, and lowering a transfer order of the data frame to the receiving terminal when the congestion display is detected at an inter-switch connection port. Data priority transfer method described. 3. A transmitting terminal for a data frame whose transfer order has been lowered by defining a credit indicating the number of frames that can be continuously transmitted, setting an upper limit value for the difference between the number of transmitted frames and the response frame, and performing flow control. Continuously transmits data frames, the reception frequency of the frames for which the congestion indication is set among the frames transferred from the receiving terminal to the port of the terminal connection switch connecting the transmitting terminal 3. The data priority transfer method according to claim 2, wherein the transmission of the response frame to the transmitting terminal is delayed according to the transmission delay to restrict the transmission to the transmitting terminal. 4. After an inter-switch connection port receives a congestion indication data frame from a terminal connection port for the first time,
It monitors the presence or absence of frame transmission to the receiving terminal in which the congestion is displayed, and when there is no frame to be transmitted to the receiving terminal for a certain period, the frame transmission order to the receiving terminal at the inter-switch connection port. 3. The data priority transfer method according to claim 2, wherein: 5. When a frame on which a congestion indication is set is received from a receiving terminal that regulates traffic at a terminal connection port, the transmitting terminal is connected even if the route differs depending on the communication direction. 3. The data according to claim 2, wherein a congestion indicator is set in a header of a frame to be transferred to a receiving terminal by a switch that is present, and congestion is notified to a switch on a transfer route from the transmitting terminal to the receiving terminal. Preferred transfer method.