KR20010046192A - Flow control method in packet switched network with shared buffer - Google Patents

Abstract

PURPOSE: A flow control method in a packet switch network having a shared buffer is provided to share buffer capacity between input ports in an Ethernet switch. CONSTITUTION: A plurality of Ethernet switches(12-1 - 12-N), upstream devices, transmit the packet data. A downstream device includes a control queue manager(130), a port control unit(110), a MAC(Media Access Control)(100), an EEPROM interface(120). Also, the downstream device has a common buffer(300). The control queue manager(130) counts the number of packets stored at present to the common buffer(30), operates a plurality of Tx Cur PKT counter 0-N(133-135) to the respective output port and also operates tow THR values(start and finish of congestion) through the EEPROM interface(120). The buffer congestion signal is updated by the control queue manager(130) whenever in queue or de queue is generated. The buffer congestion signal is transmitted from the control queue manager(130) to the port control unit(PCU)(110). The PCU(110) commands to the MAC(100) in order to form a flow control when an instruction of congestion is received.

Description

Flow Control Method in Packet Switch Network with Shared Buffer {FLOW CONTROL METHOD IN PACKET SWITCHED NETWORK WITH SHARED BUFFER}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet switched network, and in particular, to minimize packet loss on a local area network (LAN) such as Ethernet, and to reduce the bandwidth of a shared buffer. The present invention relates to a flow control method in a LAN device in which each input port is shared fairly.

Common congestion resolution methods in Ethernet include a back-pressure method and a pause frame transfer method. Dual back press method is used when Ethernet switch device is in half-duplex mode. The pause frame transmission method defined by the IEEE 802.3x standard as one of the MAC (Media Access Control) control frames is used when the full-duplex mode. Both of these techniques are congested when the buffer capacity of the Ethernet switch device reaches its limit, and flow control not to send the packet to all other Ethernet switch devices that send packets to the Ethernet switch device for the time being.

The backpress method and the pause frame transmission method of controlling flow so as not to send a packet will be described in detail as follows.

First, the back press method uses a jamming signal, which is a signal for checking a transmission collision, in a carrier sense multiple access with collision detection (CSMA / CD) access scheme. This is how any Ethernet switch device detects a jamming signal and recognizes it as a collision. When an Ethernet switch device (downstream device) becomes congested, a packet is sent to all other Ethernet switch devices (upstream devices) on the same segment for a predetermined irregular back off time by sending a back press, that is, a jamming signal. To stop the transmission.

On the other hand, the pause frame transmission method uses a pause frame, which is one of MAC control frames first defined in the IEEE 802.3x standard. In this method, when an Ethernet switch device (downstream device) becomes congested, a specific pause frame is transmitted to all other Ethernet switch devices (upstream devices) on the same segment, and the Ethernet switch devices receiving the transmitted pause frame ( Upstream devices) stop packet transmission during the pause time recorded in the pause frame.

The jamming signal of the backpress method and the frame of the pause frame transmission method are sent to all input ports, thereby preventing packets from entering the congested Ethernet switch device (downstream device) for the time being. During this period, Ethernet switch devices can eliminate congestion and prevent packet loss.

Congestion at a switch using a shared buffer is often determined by whether the buffer is full or almost full. However, when congestion is determined by this method, ports that generate a relatively small amount of traffic when the buffer is exhausted due to a particular busy port have disadvantages. In order to prevent such starvation phenomenon, a method of screening out specific Ethernet switch devices that cause congestion and then applying flow control only to the selected Ethernet switch devices is used. As a result, the Ethernet switch devices are prohibited from transmitting packets, and the other Ethernet switch devices can continue to transmit. Packets can be sent continuously in a congested state, so make sure that you have free space to store these packets.

The selective flow control method in the conventional local area network will be described with reference to the drawings;

FIG. 1 is a schematic diagram for explaining flow control in a conventional local area network. The Ethernet switch 10, 12-1, .. 12-N shown in FIG. 1 is a type of LAN device. In short, it can be called a multi-port bridge. Here, a plurality of Ethernet switches 12-1,... 12-N for transmitting packet data are referred to as "upstream devices", and jamming occurs to the plurality of Ethernet switches 12, .., 12-N when congestion occurs. It should be understood that the Ethernet switch 10 that transmits a signal (if in half duplex mode) or pause frame (if in full duplex mode) is referred to as a "downstream device".

2 is a block diagram for flow control in the conventional half-duplex communication method, Figure 3 is a block diagram for flow control in the conventional full-duplex communication method.

Referring to the configuration for the flow control in the half-duplex communication method of FIG. N input port packet counters are provided in the packet memory interface 24 of the shared buffer 20. Packet counters for each of the N input ports provided in the packet memory interface 24 are inputted through their input ports to perform an up count whenever packet data is stored in the packet memory 22 of the shared memory 20. When the packet data stored in the packet memory 22 is read and output corresponding to the input port of the self, the down count is performed. If the counter value of a predetermined input port packet counter among the input port packet counters is corresponding to or above a predetermined threshold value THR, the Ethernet switch determines that the corresponding input port may cause congestion. Take control. The preset threshold THR is provided by the host processor 26 and may be given the same value for all input ports, or may be given differently for each input port. The threshold THR may be determined differently according to traffic characteristics for each input port (eg, traffic burstness).

The MAC unit 48 includes a jamming signal generator 50, a transmission / reception block 52, and a carrier sensor 54 for flow control.

In addition, the configuration for the flow control in the full-duplex communication method of FIG. The Ethernet switch includes a shared buffer 20, a host processor 26, and a MAC unit 28. The shared buffer 20 is a packet memory 22 for storing all packet data inputted through a plurality of input ports provided in the Ethernet switch, and a packet for interfacing between the packet memory 22 and the MAC unit 28. It consists of the memory interface 24.

The host processor 26 performs various operations and state control on the MAC unit 28, and when congestion occurs, a plurality of Ethernet switches 12-1, .., 12 corresponding to an upstream device as shown in FIG. -N) transmits pause time information to suspend packet data transmission to the MAC unit 28 at initialization.

The MAC unit 28 is provided corresponding to each port of the multiports of the Ethernet switch, respectively, and performs a MAC function. As shown, the MAC unit 28 includes a pause frame generator 30, a transmission block 32, a pause timer 34, and a reception block 36. When the pause frame generator 30 receives a signal representing a buffer pool from the packet memory interface 24 of the shared buffer 20, the pause frame generator 30 uses a pause time information transmitted from the host processor 26 to provide a type of MAC control frame. An in-frame frame is configured, and the configured pause frame is transmitted to the transmission block 32. The transmission block 32 transmits the MAC control frame including the packet data read out from the shared buffer 20 or the pause frame to all Ethernets of the upstream device through the input port of the Ethernet switch corresponding to the MAC unit 28. Transmits to the switches 12-1, ..., 12-N. In addition, the transmission block 32 drives the pause timer 34. The pause timer 34 is a timer for counting an expected pause time for pausing data transmission in a plurality of Ethernet switches 12-1, .., 12-N, which are upstream devices. When the estimated pause time period is completed based on the estimated pause time and the driving command RPT_ACT, the timeout signal RPT_CPL is provided to the transmission block 32. The expected pause time period is provided by the transmission block 32. The receiving block 36 of the MAC unit 28 receives the MAC control frame transmitted from the Ethernet switch 10 which is a downstream device. When the pause frame is received among the MAC control frames, the pause timer 34 is driven using the pause time included in the pause frame. At this time, the pause timer 34 is driven based on the pause time of the reception block 36 and the driving command RXT_ACT, and counts the pause time period and provides a timeout signal RXT_CPL to the transmission block 32.

In the selective flow control method in the conventional local area network having the above configuration will be described a method for screening the ports causing the congestion; 2 and 3 and the half-duplex or full-duplex communication scheme is an output buffering structure, thereby maintaining a logical queue for each output port. If N is defined as the number of ports, there are N logical queues in the shared buffer, and as a result, the number of packets in the packet memory per input port at a certain point in time, such as when congestion occurs, is unknown. To solve this problem, we maintain N packet counters and count and store the number of incoming packets for each input port. In other words, there are N counters in the entire shared buffer. If the value of the counter is above the predefined THR value, the switch determines that this input port is likely to cause congestion and takes control action. The THR may be determined differently for each input port. This prevents congestion and ensures fair bandwidth sharing between each input port.

Currently, Ethernet switches must be able to support specified speeds for each port, and considering the limited memory speed, supporting line speeds by reducing processing time per packet is a critical problem in switch design. Most switches with shared buffers use the output queuing method, in which case a virtual input queue must be created to count the number of packets in the queue. If each input queue checks and updates an incoming or outgoing event of a packet and takes control action accordingly, this causes a burden on the processor and causes a delay in packet processing speed.

It is therefore an object of the present invention to provide a method for sharing a fair buffer capacity between each input port in an Ethernet switch.

Another object of the present invention is to provide a method for minimizing packet loss when congestion occurs in an Ethernet switch.

It is another object of the present invention to provide a method for improving packet throughput over a network.

In order to solve this problem, the present invention employs a full-duplex mode in a packet switch network, and in a flow control method in an Ethernet switch device having a shared memory storing packet data, the Ethernet switch device may be configured from a packet memory of the shared buffer. Checking a buffer state, transmitting a pause frame to an Ethernet switch device corresponding to an upstream device through an input port of the corresponding Ethernet switch device when the buffer state is buffer congestion, and a preset pause time An Ethernet switch corresponding to the upstream device through the input port of the corresponding Ethernet switch device when the buffer congestion is maintained even after the pause time has elapsed. And transmitting to the device It is characterized by consisting of tablets.

1 is a schematic diagram for explaining a flow control in a conventional local area network

2 is a block diagram for flow control in a conventional half-duplex communication method;

3 is a block diagram for flow control in a conventional full-duplex communication method;

4 is a schematic diagram for explaining flow control in a local area network according to the present invention;

5 is a block diagram for flow control in a half-duplex communication method according to a first embodiment of the present invention;

6 is a block diagram for flow control in a full duplex communication method according to a second embodiment of the present invention;

7 and 8 illustrate a flow control operation in full duplex mode according to the present invention.

9 illustrates a flow control operation in half-duplex mode according to the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same elements in the figures are represented by the same numerals wherever possible. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

4 is a schematic diagram illustrating flow control in a local area network according to the present invention;

The plurality of Ethernet switches 12-1 to 12-N transmit packet data, hereinafter, referred to as an upstream device.

In addition, when the congestion occurs, the Ethernet switch 200 which transmits a back press (when half-duplex communication mode) or a pause frame (when full-duplex communication mode) to the upstream device will be referred to as a 'downstream device'.

The downstream apparatus includes a control queue manager 130, a port control unit 110, a media access control (MAC) 100, and an e-ROM interface 120, and has a shared buffer 300.

The control queue manager 130 counts the current number of packets stored in the shared buffer 300, and operates a plurality of Tx Cur PKT counters 0 to N (133 to 135) for each output port. Two THR values (congestion start and congestion end) configured through the prompt interface 120 are operated. In the present invention, buffer congestion is represented by the number of packets in the buffers that exceed the congestion start THR value, and congestion is represented by the number of packets in the buffer that is less than the congestion end THR value. The THR values for the counters are each configured. One THR value is then assigned to the output queue. If the current number of packets destined for the output port stored in the buffer exceeds the THR value, set the corresponding bit in the Tx port congestion indication vector. Thus, the bit vector indicates output ports where the number of packets in the shared buffer is greater than the preset THR value. The buffer congestion signal is updated by the control queue manager 130 whenever an enqueue or dequeue occurs on the output queue. In addition, the buffer congestion signal is transmitted from the control queue manager 130 to a port control unit (PCU) 110.

The port control unit 110 instructs the affiliated MAC (Media Access Control) 100 to form flow control when a congestion instruction is received. If a buffer congestion (1-bit) signal is required, the MAC 100 will establish flow control without interrupting the port control unit 110. If any bit (N bit) signal of port congestion is required, the port control unit 110 first checks whether it has received itself a packet designated for the required output port. If present, the port control unit 110 instructs the MAC 100 to form flow control.

5 is a block diagram for flow control in a half-duplex communication method according to the first embodiment of the present invention, Figure 6 is a block diagram for flow control in a full-duplex communication method according to a second embodiment of the present invention to be. Detailed operations of the components illustrated in FIGS. 5 and 6 are the same as those of FIGS. 2 and 3 described with the prior art and the configuration description of FIG. 4 according to the present invention. 7 and 8 illustrate the flow control operation in the full-duplex mode according to the present invention, Figure 9 shows the flow control operation in the half-duplex mode according to the present invention.

4 to 9 will be described in detail a preferred embodiment of the present invention.

In the present invention, two independent congestion indications are used. One indicates the congestion of the shared buffer (buffer congestion), and the other indicates the congestion of the output ports (transport port) (port congestion).

First, detailed operations of the MAC 400 to perform flow control in full duplex mode are as follows.

Ethernet switch devices follow the IEEE 802.3x standard, which is full duplex. When the Ethernet switch device receives the pause frame (step 701), a new frame is not transmitted from the port during the time period set in the received pause frame (step 703). That is, when the pause frame is received, transmission of packet data is stopped. Then, the pause timer 130 is driven by using the pause time in the received pause frame. Thereafter, if the pause timer 130 times out in step 705, the process proceeds to step 709. If the pause timer 130 is driven, the operation proceeds to step 703 when the pose frame is received. If not, return to step 705. In step 709, the packet data transfer state becomes possible. Accordingly, if there is packet data to be transmitted to the Ethernet switch device corresponding to the downstream device, the Ethernet switch of the upstream device transmits the packet data.

If the input port contains more packets than the THR (threshold) value in the shared buffer, the pause frame is transmitted to the designated full-duplex port and the other frame is prohibited.

Furthermore, a pause frame transmission on buffer congestion in full duplex mode will be described;

The Ethernet switch device compares the packet data from the packet memory of the shared buffer 300 with a preset counter value, which means a buffer pool every time it enqueues or dequeues, and compares the buffer status signal with MAC. In step 801, when the MAC congestion occurs in step 803, each MAC 400 sends a pause frame to a broadcast address and a pause opcode (step 801). Opcode) and a pause frame configured to include a pause time are transmitted to the transmission block 430.

Then, the transmission block 430 transmits the pause frame to all Ethernet switches of the upstream device through the input ports of the Ethernet switch corresponding to the corresponding MAC 400. At the same time, the transmission block 430 drives the pause timer 430 (step 807).

After checking whether the pause timer 430 has timed out, and if the port timer has timed out, the process proceeds to step 811 to check whether buffer congestion is maintained through the buffer status signal received from the shared buffer 300. As a result of the check, if the buffer congestion is maintained in step 813, the process proceeds to step 815 to construct a new pause frame and transmits the new pause frame to the transmission block 430.

The MAC 400 even provides the MAC control packet transmission controller, not shown, to enable pause generation even when the transmission block 430 is paused. A control bit in the transmit status register in the MAC is set to generate a full duplex pause operation. The Command and Status Register (CSR) interface provides control and status bits in the transmit and receive control registers and the status register. Allows MAC control to be enabled and disabled, reads of flow control counters, and initialization to send MAC control frames. The pause occupancy property is added to prevent packet loss. After the pause time of the upstream device, the Ethernet switch device checks whether the buffer congestion indication is still maintained and if so generates and sends a new pause frame. For this algorithm, the RemPauseCnt field is operated in the MAC register. The RemPauseCnt represents an expected pause counter value of the upstream device as a result of the pause frame received from the current device. In this way the flow control algorithm becomes more robust. The following is a pause frame transmission algorithm. Next, look at the transmission of a pause frame on a port control unit command; When the port control unit instructs the MAC to perform flow control because of the Tx port congestion indication and the received unicast packets of the port control unit designated as the congestion port, a port control unit generates a pause frame and a broadcast address, packet opcode and pause time. Send together. The MAC block provides the MAC control packet transmission controller with enable for generating a pause even when the transmission block is paused. The control bit in the transfer status register is set to generate a full duplex pause operation. The Command and Status Register (CSR) interface provides control and status bits in the transmit and receive control registers and the status register. Allows MAC control to be enabled and disabled, reads of flow control counters, and initialization to send MAC control frames. The remote pose feature does not apply in this case. After the remote pause counter ends and the packet is received, the MAC sends a packet to the port control unit. The packet control unit 110 then determines again whether flow control is necessary.

An algorithm for transmitting a pause frame is configured as follows.

if PAUSE_Active = 0

if (buffer congestion indication is asserted

or PCU commands for flow control) then

PAUSE_active = 1

Generate a PAUSE frame as configured in host

Broadcast PAUSE frame to all the Full-Duplex ports

Assign an appropriate to RemPauseCnt

else

PAUSE_active = 0

In receiving a pause frame, the pause frame generator 410 provides pause operation enable control to enable a pause of the transmission block 430 upon reception of a MAC control packet to designate a pause operation. The MAC 400 may detect a pause frame. When a full duplex pause operation is recognized, the MAC receiving circuit loads an operation value from the pause count register and notifies the MAC engine if the pause begins at the end of the current packet. The pause circuit operates the pause counter until it decreases to zero before sending a signal at the end of the pause operation, allowing the transmission circuit to restart. The pause counter is reset with the current arithmetic value if a second full-duplex pause action is recognized while the first pose action is active.

On reception of a pose frame;

load the PauseCnt 〈--- #

if (PauseCnt is not 0) then 〈--- *

PAUSE_active = TRUE

if in the middle of a frame transmission

then complete the tx

else

decrease PauseCnt

if new PAUSE frame received then

goto # and override the pause time field

else goto *

else PAUSE_active = FALSE

Secondly, the flow control operation in the case of the half duplex mode will be described with reference to FIG. 9;

The flow control mechanism for half-duplex mode operation is as described below. If the packet counter value of any input port has more packets than the threshold value (THR) value corresponding to the corresponding input port in the shared buffer 300 in step 901, the jamming signal is assigned to the input port in step 903. Send to Further, in step 905, the jamming signal is generated as a "back press enable" to the host even though it is not transmitted by flow control.

In the reception of a jamming signal for flow control, the Ethernet switch device receiving the jamming signal individually receives the jamming signal as a result of the collision.

In addition, in the transmission of the jamming signal for flow control, if the flow control is enabled for a half-duplex mode port and the congestion port signal is enabled for indication, it will transmit the jamming signal on detection of the frame transmission of another device. Therefore, it will not allow frame transmission. More specifically, the jamming signal is sent to the input port instead of the pause frame when buffer congestion is indicated or when there is a command from the PCU or when detecting another device attached to the designated port to send the frame.

In conclusion, the present invention can be summarized in three ways as follows.

1. A LAN device that counts the number of packets in a shared buffer to predict congestion and enables flow control to upstream devices on all ports.

2. An upstream device that checks the number of packets stored in the packet memory for each output port and sends a UNICAST packet to the corresponding output port if it is above a certain threshold (THR) that can be set differently for each port. LAN device that enables flow control to the furnace.

3. LAN device, when using pause in full-duplex mode, predicts the pose time of the remote device and transmits port frames again if congestion is not resolved within the set pose time.

In the above description of the present invention, a specific embodiment such as an Ethernet switch has been described, but various modifications on the packet switch network can be implemented without departing from the scope of the present invention. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be determined by the equivalent of claims and claims.

As described above, the present invention has an advantage of improving switching performance by preventing packet loss due to congestion and ensuring fair bandwidth sharing between ports.

Claims (5)

A flow control method in an Ethernet switch device employing a full duplex mode in a packet switch network and having a shared memory for storing packet data, Checking a buffer status from the packet memory of the shared buffer in the Ethernet switch device; Transmitting a pause frame to an Ethernet switch device corresponding to an upstream device through an input port of the corresponding Ethernet switch device when the buffer state is buffer congestion; Checking whether buffer congestion is maintained when a preset pause time elapses, If buffer congestion is maintained even after the pause time has elapsed, a new buffer frame is transmitted to an Ethernet switch device corresponding to an upstream device through an input port of the corresponding Ethernet switch device. Flow control method in a packet switch network having a. The method of claim 1, In the packet switch network having a shared buffer, the buffer status is checked by a buffer status signal generated by comparing the packet data from the packet memory of the shared buffer with a preset counter value representing buffer congestion for each enqueue or dequeue. Flow control method. A flow control method in an Ethernet switch device employing a full duplex mode in a packet switch network and having a shared memory for storing packet data, Counting the number of packets stored in the packet memory of the shared buffer for each output port of the Ethernet switch device; Comparing the number of packets stored in the packet memory with a threshold set for each output port; If the number of packets stored in the packet memory is equal to or greater than a threshold set for each output port, the flow control is enabled by an Ethernet switch device corresponding to an upstream device that transmits a unicast packet to a corresponding output port. Flow control method in a packet switch network having a shared buffer characterized in that. A flow control method in an Ethernet switch device employing a half-duplex mode in a packet switch network and having a shared memory for storing packet data, Checking whether a packet counter value of an input port of the Ethernet switch device has more packets than a threshold corresponding to a corresponding input port in the shared buffer; When the packet counter value of the input port of the Ethernet switch device has more packets than the threshold corresponding to the corresponding input port in the shared buffer, a jamming signal is transmitted to the half-duplex port corresponding to the input port. A flow control method in a packet switch network having a shared buffer. The method of claim 4, wherein And the jamming signal is generated with a back press enable when it is not transmitted by the flow control.